Canadian Association of Radiologists Journal xx (2015) 1e11 www.carjonline.org
Computed Tomography / Tomodensitometrie
Postprocessing in Maxillofacial Multidetector Computed Tomography Silvio Mazziotti, MD*, Alfredo Blandino, MD, Michele Gaeta, MD, Antonio Bottari, MD, Carmelo Sofia, MD, Tommaso D’Angelo, MD, Giorgio Ascenti, MD Department of Biomedical Sciences and Morphological and Functional Imaging, University of Messina, Messina, Italy
Abstract Multidetector computed tomography (CT) and volumetric rendering techniques have always been a useful support for the anatomical and pathological study of the maxillofacial district. Nowadays accessibility to multidetector CT scanners allows the achievement of images with an extremely thin collimation and with high spatial resolution, not only along the axial plane but also along the patient’s longitudinal axis. This feature is the main theoretical assumption for multiplanar imaging and for an optimal 3-dimensional postprocessing. Multiplanar reconstruction (MPR) techniques permit images along any plane in the space to be obtained, including curved planes; this feature allows the representation in a single bidimensional image of different anatomical structures that develop on multiple planes. For this reason MPR techniques represent an unavoidable step for the study of traumatic pathology as well as of malformative, neoplastic, and inflammatory pathologies. Among 3-dimensional techniques, Maximum Intensity Projection and Shaded Surface Display are routinely used in clinical practice. In addition, volumetric rendering techniques allow a better efficacy in representing the different tissues of maxillofacial district. Each of these techniques give the radiologist an undoubted support for the diagnosis and the characterization of traumatic and malformative conditions, have a critical utility in the neoplastic evaluation of primary or secondary bone involvement, and are also used in the planning of the most modern radiosurgical treatments. The aim of this article is to define the main technical aspects of imaging postprocessing in maxillofacial CT and to summarize when each technique is indicated, according to the different pathologies of this complex anatomical district. Resume La tomodensitometrie multibarrettes et les techniques de reconstruction volumetrique ont toujours appuye efficacement les etudes anatomiques et pathologiques de la region maxillo-faciale. De nos jours, l’acces a des appareils de tomodensitometrie multibarrettes permet l’acquisition d’images par collimation extr^emement etroite et presentant une resolution spatiale tres elevee pas seulement dans le plan axial mais aussi dans l’axe longitudinal du patient. La principale hypothese qui regit l’imagerie multiplanaire et le post-traitement tridimensionnel optimal repose sur cette caracteristique. Gr^ace aux techniques de reconstruction multiplanaire, on peut obtenir des images suivant n’importe quel plan de l’espace, y compris les plans courbes, ce qui permet de representer des structures anatomiques se projetant dans plusieurs plans a l’aide d’une seule image bidimensionnelle. Pour ce motif, on utilise immanquablement des techniques de reconstruction multiplanaire pour l’examen des lesions traumatiques ainsi que des affections malformatives, neoplasiques et inflammatoires. La projection d’intensite maximale et le rendu de surface font partie des techniques de reconstruction tridimensionnelle couramment utilisees dans la pratique clinique. Par ailleurs, les techniques de rendu de volume assurent une representation efficace des differents tissus de la region maxillo-faciale. Chacune de ces techniques appuie sans contredit le radiologiste dans le diagnostic et la caracterisation des lesions traumatiques et des affections malformatives, joue un r^ole essentiel dans l’evaluation des atteintes neoplasiques primitives et secondaires des tissus osseux et sert a la planification de traitements radiochirurgicaux de pointe. Cet article a pour objectif de definir les principaux aspects techniques du posttraitement des images observees par TDM maxillo-faciale et de resumer les situations propices a chaque technique, en tenant compte des diverses lesions et affections que peut presenter cette region anatomique complexe. Ó 2015 Canadian Association of Radiologists. All rights reserved. Key Words: Multiplanar reconstruction; Maximum intensity projection; Shaded surface display; Volume rendering technique; Maxillofacial district
* Address for correspondence: Silvio Mazziotti, MD, Department of Biomedical Sciences and Morphological and Functional Imaging, University of Messina, Via Consolare Valeria, 1, 98100 Messina, Italy.
E-mail address: [email protected] (S. Mazziotti).
0846-5371/$ - see front matter Ó 2015 Canadian Association of Radiologists. All rights reserved. http://dx.doi.org/10.1016/j.carj.2014.12.004
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Table 1 Parameters of imaging acquisition for maxillofacial examinations with 16and 64-slice CT scanners
kV mAs Collimation Section thickness Kernel
16-slice CT
64-slice CT
120 200 0.75 3 mm Bone/soft tissue
120 200 0.6 3 mm Bone/soft tissue
CT ¼ computed tomography.
In the last decade the advent of multidetector technology has given a great boost to the development and use of different postprocessing imaging techniques in computed tomography (CT; 2- and 3-dimensional postprocessing) [1,2]. Among the different anatomical regions, the maxillofacial district has always gained an advantage from 2- and 3dimensional reconstruction techniques, due to its anatomical complexity. For this reason it must be remembered that even the first clinical applications of 3-dimensional rendering software used in CT were already addressed to the assessment of malformative conditions and traumatic craniofacial diseases [3]. The current availability of multidetector scanners allows the acquisition of images with an extremely thin collimation and high spatial resolution, achievable not only on the axial plane, but also along the longitudinal axis of the patient (zaxis). This feature, in combination with the achievement of a cubic voxel (isotropic voxel), is the prerequisite for multiplanar imaging with optimal postprocessing of 2- and 3dimensional volumetric data [4e8]. The rendering work on dedicated and interactive processing-consoles is becoming increasingly complex due to the greater volume of data obtained with the last-generation multidetector equipment and to the complex diagnostic questions to which the diagnostician must answer. This work is aimed at understanding the technical principles underlying the postprocessing in maxillofacial CT, an
essential condition for a correct use of the different modalities of imaging processing in the various pathological fields. Acquisition Techniques General Features The volume of acquisition, depending on the diagnostic indications, can be limited to the oral cavity, extended to the maxillofacial bones, or extended to the whole head and neck region. The acquisition parameters (summarized in Table 1 for 16- or 64-slice scanners), partially variable depending on the different scanners, must be oriented as much as possible to the isotropic resolution, a prerequisite for the maximum exploitation of the diagnostic potential deriving from the volumetric acquisition with multidetector technology, resulting in high-quality 2D and 3D reconstructions [4,5]. Before addressing the issues related to the postprocessing data management, it should be taken into account how the fast multislice CT acquisition time allows the use of some methodological tricks that, together with the 2- and 3dimensional reconstructions, are often crucial to the diagnosis (eg, puffed cheeks and open mouth acquisitions) [8e11]. In fact, the puffed cheeks scan enables a better displaying of the vestibulum oris (Figure 1A), as well as the open mouth acquisition allows a better visualization of the hard palate, otherwise inseparable from the tongue muscles (Figure 1B). Postprocessing The multiplanar reconstructions (MPR) are the most important 2D techniques for obtaining images according to any anatomical plane, even curved planes (Curved-MPR) [12e14]. The reconstructions obtained with the use of
Figure 1. ‘‘Puffed-cheek’’ computed tomography (CT) scan: multiplanar reconstruction (MPR) image obtained at the level of the superior dental arch along the axial plane (A). Superior oral vestibule (asterisks). ‘‘Open-mouth’’ CT scan: MPR image obtained along the sagittal plane (B). Hard palate (arrows). T ¼ tongue.
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Table 2 Imaging postprocessing techniques in head and neck multidetector computed tomography Clinical value Rendering technique
View Principles
MPR (ie, orthogonal-MPR; 2D curved-MPR)
VRT
3D
MIP
3D
SSD
3D
MPR images oriented along linear planes are generated by extracting and displaying only voxels positioned on the same reconstruction plane. The reconstructions following broken or curved lines are constructed in a similar way, by interpolating the image data between adjacent voxels. VRT exploits the principle of ray-casting. It uses the entire spatial and contrast information contained in the acquisition volume and represents on the resulting image a weighted average of the voxels’ intensity distributed onto each slab’s section. In a VR image to each voxel is assigned not only a value of opacity, but also one of transparency and of color, in function of its density, its location and the prospective direction in which the investigation volume is observed. The use of MIP requires the selection of a volume and a spatial orientation. In the volume selected, for each set of voxels aligned along the chosen direction, only those with higher intensity/density will be presented onto the final image, discarding the information relating to the other voxels. The SSD technique provides an image representative of the surface of a structure of interest within the volume of the acquired data. It requires the selection of a threshold for the minimum density of the voxels to be displayed in the final image, while the voxels with a lower density than the threshold will be discarded.
Advantages
Traumatic Malformative Neoplastic Inflammatory pathology pathology pathology pathology
To represent in a single þþþ bidimensional image different anatomical structures which develop on multiple planes.
þþþ
þþþ
þþþ
To represent in the same image þþþ various ranges of tissueattenuation, which are going to be illustrated in the final image with different colors and transparency according to what automatically selected in the software presets or manually chosen from the user.
þþþ
þþ
/þ
To manually select a volume and þþþ a spatial orientation in which, for each set of voxels aligned along the chosen direction, only those with higher intensity/density will be represented onto the final image, discarding the information relating to the other voxels.
þþþ
þþ
/þ
To visualize three-dimensional þþþ surfaces corresponding to the interface between voxels with an intensity higher than a selected threshold and voxels with a null resulting intensity.
þþþ
þþ
/þ
MIP ¼ maximum intensity projection; MPR ¼ multiplanar reconstruction; SSD ¼ shaded surface display; VRT ¼ volumetric rendering technique.
dedicated software for the study of dental arches (eg, Dentascan) represent a particular application of a 2D-MPR [15e18]. Among the 3D rendering techniques, the volumetric rendering technique (VRT) is a very versatile methodology,
allowing for transparency effects in addition to 3dimensional ones [19e21]. However, for representing the vascular and skeletal structures, both the maximum intensity projections (MIP) and the shaded surface display (SSD) continue to be applied (see Table 2) [21e23].
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Figure 2. Coronal multiplanar reconstruction (MPR) image (A) shows an osteolytic lesion involving the mandibular symphysis. Curved-MPR image (B), obtained along the course of both mandibular canals, better defines the extension of the osteolytic process involving both mandibular canals.
MPR MPR provides 2-dimensional images. The reformatted images oriented along linear planes are generated by extracting and displaying only those voxels positioned on the same reconstruction plane. The reconstructions following broken or curved lines are constructed in a similar way, but
Figure 3. Volumetric rendering technique image obtained using trapezoids with various colors and transparency levels which refer to different ranges of density of diverse tissues. Note the possibility to differentiate between skin surface (green), vascular structures (red), and skeletal components (white).
the image data must be interpolated between adjacent voxels. Thanks to this rendering technique it is therefore possible to represent in a single image different anatomical structures that develop on multiple planes (Figure 2). The choice of different reconstruction planes takes place in an interactive way on the workstation, by using broken lines perpendicular to a plane of the image chosen as reference. This procedure allows a simpler and more straightforward representation of the anatomy and extension of any pathological processes. It is also important to consider that a patient with head and neck pathology may adopt positions of the head in flexion and/or rotation that affect the correct positioning during the data acquisition and therefore the final result. The MPRs have, in such cases, a great importance, allowing one to regain in postprocessing the symmetrical conditions on both anatomical sides, permitting their comparison and facilitating the evaluation of the facial skeleton. MPRs normally have a thickness equivalent to a voxel. However, it is possible to create a series of images with a greater thickness compared with the original images, by carrying out an average of the various voxel intensities that correspond to different consecutive slices, the so-called Average Intensity Projection (Ave-IP); this has to be considered as an advantage because it leads to an image noise reduction and in some specific situations (eg, pediatric patients) can also be used to indirectly reduce the radiation dose [24,25]. However, it must be emphasized that the excessive thickness of MPR may lead to partial-volume effects, due to the small size of the anatomical structures represented. There must be, therefore, a continuous compromise between the noise and the thickness of the reconstruction, according to the size of the anatomical structures that are object of the study. For what concerns the odontoiatric field, specific reconstruction software (eg, Dentascan) are available and focus on
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Figure 4. Image of the maxillofacial skeleton obtained through a particular volume-rendering based technique (A) that seems to be similar to maximum intensity projection (MIP) image (B). Note the spatial depth perception appreciable on VR image, which is absent on MIP reconstruction.
the multiplanar representation of the dental arches to be applied to the presurgical planning in implant restorations [15,17,18]. VRT VRT exploits the principle of ray-casting, using the entire spatial and contrast information contained in the acquisition volume and representing on the resulting image a weighted average of the voxels’ intensity distributed onto each slab’s section [26,27]. In the VR reconstructions the density values are continuous and can vary from 0%-100%. In the creation of a VR image a density curve determines the opacity of the different tissues in relation to the average density of each voxel [27]. Thus, to each voxel is assigned not only a value of opacity, but also one of transparency and of
color, in function of its density, its location, and the prospective direction in which the investigation volume is observed. The user contributes to the final result by choosing at least 2 thresholds of densitometric values corresponding to the minimum and maximum brightness of the points displayed on the final image; the latter will depend on the density curve that can be drawn manually or simply selected from the software presets, which in turn can then be partially changed [28]. The simplest technique requires that the relationship between the density of 2 voxels on the original images and the intensity of the corresponding pixels on the VR images should be constant (linear transfer function). As an alternative, the operator may define personalized transfer functions (complex functions with multiple thresholds) by using trapezoids, modifiable in shape, height and position on the CT
Figure 5. Myxofibroma of the mandible in a pediatric patient. Coronal multiplanar reconstruction image (A) shows an expansive osteolytic lesion in the right mandibular ramus. Volumetric rendering technique images better define the morphology of the osteolytic lesion: using too high resolution kernel may cause blurring artifacts (B), rather than using a lower one (C).
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MIP
Figure 6. Thin maximum intensity projection image obtained along a sagittal-oblique plane showing a fracture of the mandibular angle.
scale, to represent the various ranges of tissue-attenuation, which are going to be illustrated in the final image with different colors (Figure 3). With the VRT one may obtain visualizations similar to MIP (Figure 4) or SSD reconstructions, in relation to the gradient of shading used to simulate reflectivity. The choice of the correct convolution kernel (or reconstruction algorithm) contributes to the final result. The choice of the kernel determines a compromise between the spatial resolution and the contrast. High-resolution kernel always causes an increase in noise with a reduced contrast resolution, which then translates into a lower discrimination of density between the different tissues, a not so favorable situation for reconstruction techniques basing their principles on the attribution of density or density thresholds (Figure 5).
The use of MIP requires the selection, done by the operator, of a volume and a spatial orientation. In the volume selected, for each set of voxels aligned along the chosen direction, only those with higher intensity/density will be represented onto the final image, discarding the information relating to the other voxels [27]. The elimination of the voxels with a not maximum intensity determines the loss of information relating to the spatial depth and contrast between objects of different density in the reconstruction volume (Figure 4B). MIP reconstructions are primarily used in the representation of skeletal structures. To obtain an improved quality of the reconstructed image, free from an overlap between the different bone components, it may be useful to select, within the volume of acquisition, a sub-volume (slab) of adequate thickness (Figure 6). This precaution also allows a better representation of the vascular structures which, having a similar density to bone in the postcontrastographic acquisitions, are likely to experience the phenomena of overlapping with facial bones. This problem can also be solved by using bone-subtraction techniques. SSD The SSD technique provides a 3-dimensional image representative of the surface of a structure of interest within the volume of the acquired data. The 3-dimensional display is finally obtained as if the structure were lit by 1 or more sources of virtual external illumination, following the user’s directions. The 3-dimensional representation of the structures of interest requires the selection of a threshold for the minimum density of the voxels to be displayed in the final image, while the voxels with a lower density than the threshold will be discarded [29,30]. This selection
Figure 7. Shaded surface display image of the maxillofacial skeleton. It is possible to identify circumscribed bone ‘‘pseudodefects’’ of the orbital floors and of the anterior walls of maxillary sinuses (A). Lowering of the threshold value eliminates bone ‘‘pseudodefects,’’ although it could cause the appearance of the ‘‘flying pixels’’ (B). Bone ‘‘pseudodefects’’ can increase by raising up the segmentation threshold value (C).
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Figure 8. Craniofacial trauma. Preoperative computed tomography (CT) scan: the shaded surface display (SSD) image of maxillofacial skeleton shows dislocated multiple fracture fragments (A). Face deformity is also appreciated through SSD image of skin (B). Postoperative CT scan: the SSD image of maxillofacial skeleton (C) and of skin surface (D) shows the reduction of fractures using osteosynthesis material (miniplates) and the restoring of facial aesthetics.
procedure, called segmentation, may present a varying complexity in relation to the contrast of the structure that must be displayed. The reconstructed image will be formed by the surfaces corresponding to the interface between voxels with an intensity higher than the threshold and voxels with a null resulting intensity. The threshold value is the average of the density values of the structure to be represented and those of the surrounding structures [28]. In the representation of the facial bone skeleton a good compromise in the choice of the threshold value is 150 HU. However, it must be remembered that only structures with a thickness greater than that of the section will be represented in their real dimension. Relatively small or thin
details, especially if oriented parallel to the scan plane can lose contrast, due to the partial-volume effect until they disappear completely. In the representation of the facial bone skeleton this latter effect may cause bone pseudodefects, more frequently significant at the level of the orbital floor or the anterior wall of the maxillary sinus (Figure 7A). The partial-volume effects may be partly compensated by lowering the threshold segmentation. A too low threshold value, however, causes the appearance of the so-called ‘‘flying pixels’’ related to the voxels that, by exceeding the threshold value, will be represented in the final image superimposing other anatomical structures (Figure 7B). On the contrary, to an excessive increase in the threshold value
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Figure 9. Pierre-Robin malformation. Shaded surface display (SSD) image of maxillofacial skeleton (A) demonstrates a complex facial malformation, particularly evident in the mandible, which presents hypoplasia of horizontal rami, severe maxillary prognathism, condylar hypoplasia, and anteriorly dislocated condyles inside a less concave than normal mandibular fossa. There is evidence of a previous maxillo-malar osteotomy. SSD image of the skin surface (B) shows the typical facial aspect.
corresponds a greater extension of the bone pseudodefects (Figure 7C).
processes thus easing the multidisciplinary management of the patient [31].
Clinical Applications
Traumatic Pathology
The wide choice of image reconstruction modalities requires a targeted use of each postprocessing technique for the various fields of maxillofacial pathology. The diagnostic evaluation in maxillofacial pathology is mainly based on the interactive multiplanar analysis, which facilitates the recognition of anatomical structures and pathological changes, difficult to evaluate only on the axial plane. As regards the 3-dimensional processing, though not increasing the information contents of the multiplanar analysis, it significantly increases the spatial evaluation, especially for what concerns malformative and traumatic pathology. In these cases, in fact, the 3D postprocessing facilitates the radiologist’s conscious and unconscious mental
MPRs easily allow to identify fractures and to evaluate the dislocation of bone fragments and any possible involvement of the adjacent soft tissues [32,33]. In fact, one of the main aims of the radiologist is to supply as much information as possible regarding the spatial arrangement of the single skeletal fragments to the maxillofacial surgeon, together with the direction and magnitude of their displacement. All the 3-dimensional reconstruction techniques available may however be used to better demonstrate how the traumatic event occurred and to lead out the most appropriate surgical approach to reposition the bone fragments, in order to reduce the fractures. The surgeon, in fact, must reposition the skeletal segments maintaining, as far as possible, the original 3-dimensional arrangement in an
Figure 10. Adenoid cystic carcinoma of the right soft palate with perineural invasion. Axial computed tomography image (A) and multiplanar reconstruction image of the facial bones along the coronal plane (B) show the enlargement of the right major palatine foramen (asterisk in A) and of pterygopalatine canal (arrow in B), as signs of perineural spread through palatine nerves.
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Figure 11. Multiplanar reconstruction image (A) and volumetric rendering technique image (B) are used in Cyberknife radiosurgical treatment of postsurgical recidive of adenoid cystic carcinoma of the palate, in this case occurring in the right apex of orbital cavity (same patient as in Figure 10).
attempt to restore the pre-existing aesthetic and functional features (Figure 8) [34]. Malformative Pathology Even in maxillofacial malformations, especially if they extend to the skull base, the damage can be functional as well as aesthetic. The use of the techniques of 2- and 3dimensional reconstruction is therefore essential to the diagnostic framework, by providing a global view of a malformative syndrome for planning a more accurate surgical and/or orthodontic treatment (Figure 9) [35e38]. The postprocessing of data acquired with a multidetector CT, also including presurgery simulation (surgery on models), permits a more focused planning and quantification of the bone grafting and/or biomaterials to be used, allowing the surgeon a greater precision in the plastic reconstruction and a sharp reduction in the duration of surgery [36].
primarily related to the evaluation of the tumor extension in depth, to those structures that are often inaccessible to direct clinical evaluation. MPR, in such a complex anatomical region, allows a detailed analysis of the pathological involvement of the different structures and, in addition, the identification of specific spreading pathways (ie, perineural or perivascular) (Figure 10) [39e42]. 3D reconstruction techniques have a critical utility in the evaluation of primary or secondary bone involvement, above all when this is limited in its extension, thus helping in the choice of the skeletal resection margins and allowing for a greater accuracy in the planning of the prosthetic remodeling with synthetic material [31]. Furthermore, 3D applications are also useful in the planning of the most modern radio-surgical treatments, such as those carried out with the Cyberknife apparatus (Figure 11) [10,43]. Inflammatory Pathology
Neoplastic Pathology The diagnostic challenges related to the maxillofacial tumors, other than evaluation of the onset location, are
The primary inflammatory disease of maxillofacial bones is overall essentially rare. It consists of a few entities such as osteitis and osteonecrosis.
Figure 12. Odontogenic inflammation. Multiplanar reconstruction (MPR) image of the maxillofacial bones obtained along an oblique-coronal plane (A) shows an osteolytic area near the apex of 4.6, with cortical erosion of the mandible in its lingual side (arrow). MPR image, performed after i.v. contrast medium injection and obtained with soft tissue kernel (B), shows a voluminous abscess in the submandibular space (asterisk), enclosed cranially by the mylohyoid muscle (arrows) and sparing the sublingual space.
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The former may result from an odontogenic pathology or be an expression of complications of fracture lesions or surgery, while the necrosis may have iatrogenic causes, such as radionecrosis or the one induced in the maxillary bones by use of bisphosphonates [44]. In these cases, the 2dimensional multiplanar evaluation successfully aims at the identification of the original inflammatory outbreak and the definition of the extension of the inflammatory process to the adjacent spaces (Figure 12); the use of 3-dimensional reconstruction techniques is often unnecessary. Conclusions The knowledge of technical principles underlying the 3dimensional and multiplanar imaging is the prerequisite for a correct application of the reconstruction algorithms. In fact, the use of an incorrect or not sufficiently adequate reconstruction algorithm for the specific diseases (traumatic, malformative, neoplastic, inflammatory pathology), along with an improper setting of the reconstruction parameters, may result in a suboptimal quality of the diagnostic image. References [1] Flohr TG, Schaller S, Stierstorfer K, Bruder H, Ohnesorge BM, Schoepf UJ. Multi-detector row CT systems and image-reconstruction techniques. Radiology 2005;235:756e73. [2] Mazziotti S, Racchiusa S, Settineri N, Vinci S, Salamone I, Pandolfo I. Head and neck radiology: role of multidetector computed tomography in the evaluation of the tympanic canaliculus. Radiol Med 2011;116:657e66. [3] Vannier MW, Marsh JL, Warren JO. Three-dimensional CT reconstruction images for craniofacial surgical planning and evaluation. Radiology 1984;150:179e84. [4] Darlymple NC, Prasad SR, El-Merhi FM, Chintapalli KN. Price of isotropy in multi detector CT. Radiographics 2007;27:49e62. [5] Flohr T, Stierstorfer K, Bruder H, Simon J, Schaller S. New technical developments in multislice CTePart 1: Approaching isotropic resolution with sub-millimeter 16-slice scanning. Rofo 2002;174:839e45. [6] Perandini S, Faccioli N, Zaccarella A, Re TJ, Pozzi Mucelli R. The diagnostic contribution of CT volumetric rendering techniques in routine practice. Indian J Radiol Imaging 2010;20:92e7. [7] Choplin RH, Buckwalter KA, Rydberg J, Farber JM. CT with 3D rendering of the tendons of the foot and ankle: technique, normal anatomy and disease. Radiographics 2004;24:343e56. [8] Henrot P, Blum A, Toussaint B, Troufleau P, Stines J, Roland J. Dynamic maneuvers in local staging of head and neck malignancies with current imaging techniques: principles and clinical applications. Radiographics 2003;23:1201e13. [9] Weissman JL, Carrau RL. ‘‘Puffed-cheek’’ CT improves evaluation of the oral cavity. Am J Neuroradiol 2001;22:741e4. [10] Mazziotti S, Ascenti G, Scribano E, et al. CT-MR integrated diagnostic imaging of the oral cavity: neoplastic disease. Radiol Med 2013;118: 123e39. [11] Celebi I, Oz A, Sasani M, et al. Using dynamic maneuvers in the computed tomography/magnetic resonance assessment of lesions of the head and neck. Can Assoc Radiol J 2013;64:351e7. [12] De Filippo M, Onniboni M, Rusca M, Carbognani P, Ferrari L, Guazzi A. Adventages of multidetector-row CT with multiplanar reformation in guiding percutaneous lung biopsies. Radiol Med 2008; 113:945e53. [13] Mazziotti S, Arceri F, Vinci S, Salamone I, Racchiusa S, Pandolfo I. Role of coronal oblique reconstructions as a complement to CT study of the temporal bone: normal anatomy. Radiol Med 2006;111:607e17.
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Postprocessing in maxillofacial MDCT / Canadian Association of Radiologists Journal xx (2015) 1e11 [38] Mazziotti S, D’Angelo T, Ascenti G, Blandino A. Facial abnormalities in nablus mask-like facial syndrome: multidetector computed tomography findings. J Oral Maxillofac Surg 2014;72: 1579e84. [39] D’Angelo T, Blandino A, Ascenti G, Vinci S, Gaeta M, Mazziotti S. Solitary metastasis of renal cell carcinoma in infratemporal fossa. Clin Imaging 2015;39:155e7. [40] Maroldi R, Battaglia G, Farina D, Maculotti P, Chiesa A. Tumours of the oropharynx and oral cavity: perineural spread and bone invasion. JBR-BTR 1999;82:294e300.
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[41] Caldemeyer KS, Mathews VP, Righi PD, Smith RR. Imaging features and clinical significance of perineural spread or extension of head and neck tumors. Radiographics 1998;18:97e110. [42] Mazziotti S, Pandolfo I, D’Angelo T, et al. Diagnostic approach to retromolar trigone cancer by multiplanar computed tomography reconstructions. Can Assoc Radiolog J 2014;65:335e44. [43] Conti A, Pontoriero A, Salamone I, et al. Protecting venous structures during radiosurgery for parasagittal meningiomas. Neurosurg Focus 2009;27:11. [44] Gonzalez-Beicos A, Nunez D. Imaging of acute head and neck infections. Radiol Clin North Am 2012;50:73e83.
Computed Tomography / Tomodensitometrie
Postprocessing in Maxillofacial Multidetector Computed Tomography Silvio Mazziotti, MD*, Alfredo Blandino, MD, Michele Gaeta, MD, Antonio Bottari, MD, Carmelo Sofia, MD, Tommaso D’Angelo, MD, Giorgio Ascenti, MD Department of Biomedical Sciences and Morphological and Functional Imaging, University of Messina, Messina, Italy
Abstract Multidetector computed tomography (CT) and volumetric rendering techniques have always been a useful support for the anatomical and pathological study of the maxillofacial district. Nowadays accessibility to multidetector CT scanners allows the achievement of images with an extremely thin collimation and with high spatial resolution, not only along the axial plane but also along the patient’s longitudinal axis. This feature is the main theoretical assumption for multiplanar imaging and for an optimal 3-dimensional postprocessing. Multiplanar reconstruction (MPR) techniques permit images along any plane in the space to be obtained, including curved planes; this feature allows the representation in a single bidimensional image of different anatomical structures that develop on multiple planes. For this reason MPR techniques represent an unavoidable step for the study of traumatic pathology as well as of malformative, neoplastic, and inflammatory pathologies. Among 3-dimensional techniques, Maximum Intensity Projection and Shaded Surface Display are routinely used in clinical practice. In addition, volumetric rendering techniques allow a better efficacy in representing the different tissues of maxillofacial district. Each of these techniques give the radiologist an undoubted support for the diagnosis and the characterization of traumatic and malformative conditions, have a critical utility in the neoplastic evaluation of primary or secondary bone involvement, and are also used in the planning of the most modern radiosurgical treatments. The aim of this article is to define the main technical aspects of imaging postprocessing in maxillofacial CT and to summarize when each technique is indicated, according to the different pathologies of this complex anatomical district. Resume La tomodensitometrie multibarrettes et les techniques de reconstruction volumetrique ont toujours appuye efficacement les etudes anatomiques et pathologiques de la region maxillo-faciale. De nos jours, l’acces a des appareils de tomodensitometrie multibarrettes permet l’acquisition d’images par collimation extr^emement etroite et presentant une resolution spatiale tres elevee pas seulement dans le plan axial mais aussi dans l’axe longitudinal du patient. La principale hypothese qui regit l’imagerie multiplanaire et le post-traitement tridimensionnel optimal repose sur cette caracteristique. Gr^ace aux techniques de reconstruction multiplanaire, on peut obtenir des images suivant n’importe quel plan de l’espace, y compris les plans courbes, ce qui permet de representer des structures anatomiques se projetant dans plusieurs plans a l’aide d’une seule image bidimensionnelle. Pour ce motif, on utilise immanquablement des techniques de reconstruction multiplanaire pour l’examen des lesions traumatiques ainsi que des affections malformatives, neoplasiques et inflammatoires. La projection d’intensite maximale et le rendu de surface font partie des techniques de reconstruction tridimensionnelle couramment utilisees dans la pratique clinique. Par ailleurs, les techniques de rendu de volume assurent une representation efficace des differents tissus de la region maxillo-faciale. Chacune de ces techniques appuie sans contredit le radiologiste dans le diagnostic et la caracterisation des lesions traumatiques et des affections malformatives, joue un r^ole essentiel dans l’evaluation des atteintes neoplasiques primitives et secondaires des tissus osseux et sert a la planification de traitements radiochirurgicaux de pointe. Cet article a pour objectif de definir les principaux aspects techniques du posttraitement des images observees par TDM maxillo-faciale et de resumer les situations propices a chaque technique, en tenant compte des diverses lesions et affections que peut presenter cette region anatomique complexe. Ó 2015 Canadian Association of Radiologists. All rights reserved. Key Words: Multiplanar reconstruction; Maximum intensity projection; Shaded surface display; Volume rendering technique; Maxillofacial district
* Address for correspondence: Silvio Mazziotti, MD, Department of Biomedical Sciences and Morphological and Functional Imaging, University of Messina, Via Consolare Valeria, 1, 98100 Messina, Italy.
E-mail address: [email protected] (S. Mazziotti).
0846-5371/$ - see front matter Ó 2015 Canadian Association of Radiologists. All rights reserved. http://dx.doi.org/10.1016/j.carj.2014.12.004
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Table 1 Parameters of imaging acquisition for maxillofacial examinations with 16and 64-slice CT scanners
kV mAs Collimation Section thickness Kernel
16-slice CT
64-slice CT
120 200 0.75 3 mm Bone/soft tissue
120 200 0.6 3 mm Bone/soft tissue
CT ¼ computed tomography.
In the last decade the advent of multidetector technology has given a great boost to the development and use of different postprocessing imaging techniques in computed tomography (CT; 2- and 3-dimensional postprocessing) [1,2]. Among the different anatomical regions, the maxillofacial district has always gained an advantage from 2- and 3dimensional reconstruction techniques, due to its anatomical complexity. For this reason it must be remembered that even the first clinical applications of 3-dimensional rendering software used in CT were already addressed to the assessment of malformative conditions and traumatic craniofacial diseases [3]. The current availability of multidetector scanners allows the acquisition of images with an extremely thin collimation and high spatial resolution, achievable not only on the axial plane, but also along the longitudinal axis of the patient (zaxis). This feature, in combination with the achievement of a cubic voxel (isotropic voxel), is the prerequisite for multiplanar imaging with optimal postprocessing of 2- and 3dimensional volumetric data [4e8]. The rendering work on dedicated and interactive processing-consoles is becoming increasingly complex due to the greater volume of data obtained with the last-generation multidetector equipment and to the complex diagnostic questions to which the diagnostician must answer. This work is aimed at understanding the technical principles underlying the postprocessing in maxillofacial CT, an
essential condition for a correct use of the different modalities of imaging processing in the various pathological fields. Acquisition Techniques General Features The volume of acquisition, depending on the diagnostic indications, can be limited to the oral cavity, extended to the maxillofacial bones, or extended to the whole head and neck region. The acquisition parameters (summarized in Table 1 for 16- or 64-slice scanners), partially variable depending on the different scanners, must be oriented as much as possible to the isotropic resolution, a prerequisite for the maximum exploitation of the diagnostic potential deriving from the volumetric acquisition with multidetector technology, resulting in high-quality 2D and 3D reconstructions [4,5]. Before addressing the issues related to the postprocessing data management, it should be taken into account how the fast multislice CT acquisition time allows the use of some methodological tricks that, together with the 2- and 3dimensional reconstructions, are often crucial to the diagnosis (eg, puffed cheeks and open mouth acquisitions) [8e11]. In fact, the puffed cheeks scan enables a better displaying of the vestibulum oris (Figure 1A), as well as the open mouth acquisition allows a better visualization of the hard palate, otherwise inseparable from the tongue muscles (Figure 1B). Postprocessing The multiplanar reconstructions (MPR) are the most important 2D techniques for obtaining images according to any anatomical plane, even curved planes (Curved-MPR) [12e14]. The reconstructions obtained with the use of
Figure 1. ‘‘Puffed-cheek’’ computed tomography (CT) scan: multiplanar reconstruction (MPR) image obtained at the level of the superior dental arch along the axial plane (A). Superior oral vestibule (asterisks). ‘‘Open-mouth’’ CT scan: MPR image obtained along the sagittal plane (B). Hard palate (arrows). T ¼ tongue.
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Table 2 Imaging postprocessing techniques in head and neck multidetector computed tomography Clinical value Rendering technique
View Principles
MPR (ie, orthogonal-MPR; 2D curved-MPR)
VRT
3D
MIP
3D
SSD
3D
MPR images oriented along linear planes are generated by extracting and displaying only voxels positioned on the same reconstruction plane. The reconstructions following broken or curved lines are constructed in a similar way, by interpolating the image data between adjacent voxels. VRT exploits the principle of ray-casting. It uses the entire spatial and contrast information contained in the acquisition volume and represents on the resulting image a weighted average of the voxels’ intensity distributed onto each slab’s section. In a VR image to each voxel is assigned not only a value of opacity, but also one of transparency and of color, in function of its density, its location and the prospective direction in which the investigation volume is observed. The use of MIP requires the selection of a volume and a spatial orientation. In the volume selected, for each set of voxels aligned along the chosen direction, only those with higher intensity/density will be presented onto the final image, discarding the information relating to the other voxels. The SSD technique provides an image representative of the surface of a structure of interest within the volume of the acquired data. It requires the selection of a threshold for the minimum density of the voxels to be displayed in the final image, while the voxels with a lower density than the threshold will be discarded.
Advantages
Traumatic Malformative Neoplastic Inflammatory pathology pathology pathology pathology
To represent in a single þþþ bidimensional image different anatomical structures which develop on multiple planes.
þþþ
þþþ
þþþ
To represent in the same image þþþ various ranges of tissueattenuation, which are going to be illustrated in the final image with different colors and transparency according to what automatically selected in the software presets or manually chosen from the user.
þþþ
þþ
/þ
To manually select a volume and þþþ a spatial orientation in which, for each set of voxels aligned along the chosen direction, only those with higher intensity/density will be represented onto the final image, discarding the information relating to the other voxels.
þþþ
þþ
/þ
To visualize three-dimensional þþþ surfaces corresponding to the interface between voxels with an intensity higher than a selected threshold and voxels with a null resulting intensity.
þþþ
þþ
/þ
MIP ¼ maximum intensity projection; MPR ¼ multiplanar reconstruction; SSD ¼ shaded surface display; VRT ¼ volumetric rendering technique.
dedicated software for the study of dental arches (eg, Dentascan) represent a particular application of a 2D-MPR [15e18]. Among the 3D rendering techniques, the volumetric rendering technique (VRT) is a very versatile methodology,
allowing for transparency effects in addition to 3dimensional ones [19e21]. However, for representing the vascular and skeletal structures, both the maximum intensity projections (MIP) and the shaded surface display (SSD) continue to be applied (see Table 2) [21e23].
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Figure 2. Coronal multiplanar reconstruction (MPR) image (A) shows an osteolytic lesion involving the mandibular symphysis. Curved-MPR image (B), obtained along the course of both mandibular canals, better defines the extension of the osteolytic process involving both mandibular canals.
MPR MPR provides 2-dimensional images. The reformatted images oriented along linear planes are generated by extracting and displaying only those voxels positioned on the same reconstruction plane. The reconstructions following broken or curved lines are constructed in a similar way, but
Figure 3. Volumetric rendering technique image obtained using trapezoids with various colors and transparency levels which refer to different ranges of density of diverse tissues. Note the possibility to differentiate between skin surface (green), vascular structures (red), and skeletal components (white).
the image data must be interpolated between adjacent voxels. Thanks to this rendering technique it is therefore possible to represent in a single image different anatomical structures that develop on multiple planes (Figure 2). The choice of different reconstruction planes takes place in an interactive way on the workstation, by using broken lines perpendicular to a plane of the image chosen as reference. This procedure allows a simpler and more straightforward representation of the anatomy and extension of any pathological processes. It is also important to consider that a patient with head and neck pathology may adopt positions of the head in flexion and/or rotation that affect the correct positioning during the data acquisition and therefore the final result. The MPRs have, in such cases, a great importance, allowing one to regain in postprocessing the symmetrical conditions on both anatomical sides, permitting their comparison and facilitating the evaluation of the facial skeleton. MPRs normally have a thickness equivalent to a voxel. However, it is possible to create a series of images with a greater thickness compared with the original images, by carrying out an average of the various voxel intensities that correspond to different consecutive slices, the so-called Average Intensity Projection (Ave-IP); this has to be considered as an advantage because it leads to an image noise reduction and in some specific situations (eg, pediatric patients) can also be used to indirectly reduce the radiation dose [24,25]. However, it must be emphasized that the excessive thickness of MPR may lead to partial-volume effects, due to the small size of the anatomical structures represented. There must be, therefore, a continuous compromise between the noise and the thickness of the reconstruction, according to the size of the anatomical structures that are object of the study. For what concerns the odontoiatric field, specific reconstruction software (eg, Dentascan) are available and focus on
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Figure 4. Image of the maxillofacial skeleton obtained through a particular volume-rendering based technique (A) that seems to be similar to maximum intensity projection (MIP) image (B). Note the spatial depth perception appreciable on VR image, which is absent on MIP reconstruction.
the multiplanar representation of the dental arches to be applied to the presurgical planning in implant restorations [15,17,18]. VRT VRT exploits the principle of ray-casting, using the entire spatial and contrast information contained in the acquisition volume and representing on the resulting image a weighted average of the voxels’ intensity distributed onto each slab’s section [26,27]. In the VR reconstructions the density values are continuous and can vary from 0%-100%. In the creation of a VR image a density curve determines the opacity of the different tissues in relation to the average density of each voxel [27]. Thus, to each voxel is assigned not only a value of opacity, but also one of transparency and of
color, in function of its density, its location, and the prospective direction in which the investigation volume is observed. The user contributes to the final result by choosing at least 2 thresholds of densitometric values corresponding to the minimum and maximum brightness of the points displayed on the final image; the latter will depend on the density curve that can be drawn manually or simply selected from the software presets, which in turn can then be partially changed [28]. The simplest technique requires that the relationship between the density of 2 voxels on the original images and the intensity of the corresponding pixels on the VR images should be constant (linear transfer function). As an alternative, the operator may define personalized transfer functions (complex functions with multiple thresholds) by using trapezoids, modifiable in shape, height and position on the CT
Figure 5. Myxofibroma of the mandible in a pediatric patient. Coronal multiplanar reconstruction image (A) shows an expansive osteolytic lesion in the right mandibular ramus. Volumetric rendering technique images better define the morphology of the osteolytic lesion: using too high resolution kernel may cause blurring artifacts (B), rather than using a lower one (C).
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MIP
Figure 6. Thin maximum intensity projection image obtained along a sagittal-oblique plane showing a fracture of the mandibular angle.
scale, to represent the various ranges of tissue-attenuation, which are going to be illustrated in the final image with different colors (Figure 3). With the VRT one may obtain visualizations similar to MIP (Figure 4) or SSD reconstructions, in relation to the gradient of shading used to simulate reflectivity. The choice of the correct convolution kernel (or reconstruction algorithm) contributes to the final result. The choice of the kernel determines a compromise between the spatial resolution and the contrast. High-resolution kernel always causes an increase in noise with a reduced contrast resolution, which then translates into a lower discrimination of density between the different tissues, a not so favorable situation for reconstruction techniques basing their principles on the attribution of density or density thresholds (Figure 5).
The use of MIP requires the selection, done by the operator, of a volume and a spatial orientation. In the volume selected, for each set of voxels aligned along the chosen direction, only those with higher intensity/density will be represented onto the final image, discarding the information relating to the other voxels [27]. The elimination of the voxels with a not maximum intensity determines the loss of information relating to the spatial depth and contrast between objects of different density in the reconstruction volume (Figure 4B). MIP reconstructions are primarily used in the representation of skeletal structures. To obtain an improved quality of the reconstructed image, free from an overlap between the different bone components, it may be useful to select, within the volume of acquisition, a sub-volume (slab) of adequate thickness (Figure 6). This precaution also allows a better representation of the vascular structures which, having a similar density to bone in the postcontrastographic acquisitions, are likely to experience the phenomena of overlapping with facial bones. This problem can also be solved by using bone-subtraction techniques. SSD The SSD technique provides a 3-dimensional image representative of the surface of a structure of interest within the volume of the acquired data. The 3-dimensional display is finally obtained as if the structure were lit by 1 or more sources of virtual external illumination, following the user’s directions. The 3-dimensional representation of the structures of interest requires the selection of a threshold for the minimum density of the voxels to be displayed in the final image, while the voxels with a lower density than the threshold will be discarded [29,30]. This selection
Figure 7. Shaded surface display image of the maxillofacial skeleton. It is possible to identify circumscribed bone ‘‘pseudodefects’’ of the orbital floors and of the anterior walls of maxillary sinuses (A). Lowering of the threshold value eliminates bone ‘‘pseudodefects,’’ although it could cause the appearance of the ‘‘flying pixels’’ (B). Bone ‘‘pseudodefects’’ can increase by raising up the segmentation threshold value (C).
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Figure 8. Craniofacial trauma. Preoperative computed tomography (CT) scan: the shaded surface display (SSD) image of maxillofacial skeleton shows dislocated multiple fracture fragments (A). Face deformity is also appreciated through SSD image of skin (B). Postoperative CT scan: the SSD image of maxillofacial skeleton (C) and of skin surface (D) shows the reduction of fractures using osteosynthesis material (miniplates) and the restoring of facial aesthetics.
procedure, called segmentation, may present a varying complexity in relation to the contrast of the structure that must be displayed. The reconstructed image will be formed by the surfaces corresponding to the interface between voxels with an intensity higher than the threshold and voxels with a null resulting intensity. The threshold value is the average of the density values of the structure to be represented and those of the surrounding structures [28]. In the representation of the facial bone skeleton a good compromise in the choice of the threshold value is 150 HU. However, it must be remembered that only structures with a thickness greater than that of the section will be represented in their real dimension. Relatively small or thin
details, especially if oriented parallel to the scan plane can lose contrast, due to the partial-volume effect until they disappear completely. In the representation of the facial bone skeleton this latter effect may cause bone pseudodefects, more frequently significant at the level of the orbital floor or the anterior wall of the maxillary sinus (Figure 7A). The partial-volume effects may be partly compensated by lowering the threshold segmentation. A too low threshold value, however, causes the appearance of the so-called ‘‘flying pixels’’ related to the voxels that, by exceeding the threshold value, will be represented in the final image superimposing other anatomical structures (Figure 7B). On the contrary, to an excessive increase in the threshold value
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Figure 9. Pierre-Robin malformation. Shaded surface display (SSD) image of maxillofacial skeleton (A) demonstrates a complex facial malformation, particularly evident in the mandible, which presents hypoplasia of horizontal rami, severe maxillary prognathism, condylar hypoplasia, and anteriorly dislocated condyles inside a less concave than normal mandibular fossa. There is evidence of a previous maxillo-malar osteotomy. SSD image of the skin surface (B) shows the typical facial aspect.
corresponds a greater extension of the bone pseudodefects (Figure 7C).
processes thus easing the multidisciplinary management of the patient [31].
Clinical Applications
Traumatic Pathology
The wide choice of image reconstruction modalities requires a targeted use of each postprocessing technique for the various fields of maxillofacial pathology. The diagnostic evaluation in maxillofacial pathology is mainly based on the interactive multiplanar analysis, which facilitates the recognition of anatomical structures and pathological changes, difficult to evaluate only on the axial plane. As regards the 3-dimensional processing, though not increasing the information contents of the multiplanar analysis, it significantly increases the spatial evaluation, especially for what concerns malformative and traumatic pathology. In these cases, in fact, the 3D postprocessing facilitates the radiologist’s conscious and unconscious mental
MPRs easily allow to identify fractures and to evaluate the dislocation of bone fragments and any possible involvement of the adjacent soft tissues [32,33]. In fact, one of the main aims of the radiologist is to supply as much information as possible regarding the spatial arrangement of the single skeletal fragments to the maxillofacial surgeon, together with the direction and magnitude of their displacement. All the 3-dimensional reconstruction techniques available may however be used to better demonstrate how the traumatic event occurred and to lead out the most appropriate surgical approach to reposition the bone fragments, in order to reduce the fractures. The surgeon, in fact, must reposition the skeletal segments maintaining, as far as possible, the original 3-dimensional arrangement in an
Figure 10. Adenoid cystic carcinoma of the right soft palate with perineural invasion. Axial computed tomography image (A) and multiplanar reconstruction image of the facial bones along the coronal plane (B) show the enlargement of the right major palatine foramen (asterisk in A) and of pterygopalatine canal (arrow in B), as signs of perineural spread through palatine nerves.
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Figure 11. Multiplanar reconstruction image (A) and volumetric rendering technique image (B) are used in Cyberknife radiosurgical treatment of postsurgical recidive of adenoid cystic carcinoma of the palate, in this case occurring in the right apex of orbital cavity (same patient as in Figure 10).
attempt to restore the pre-existing aesthetic and functional features (Figure 8) [34]. Malformative Pathology Even in maxillofacial malformations, especially if they extend to the skull base, the damage can be functional as well as aesthetic. The use of the techniques of 2- and 3dimensional reconstruction is therefore essential to the diagnostic framework, by providing a global view of a malformative syndrome for planning a more accurate surgical and/or orthodontic treatment (Figure 9) [35e38]. The postprocessing of data acquired with a multidetector CT, also including presurgery simulation (surgery on models), permits a more focused planning and quantification of the bone grafting and/or biomaterials to be used, allowing the surgeon a greater precision in the plastic reconstruction and a sharp reduction in the duration of surgery [36].
primarily related to the evaluation of the tumor extension in depth, to those structures that are often inaccessible to direct clinical evaluation. MPR, in such a complex anatomical region, allows a detailed analysis of the pathological involvement of the different structures and, in addition, the identification of specific spreading pathways (ie, perineural or perivascular) (Figure 10) [39e42]. 3D reconstruction techniques have a critical utility in the evaluation of primary or secondary bone involvement, above all when this is limited in its extension, thus helping in the choice of the skeletal resection margins and allowing for a greater accuracy in the planning of the prosthetic remodeling with synthetic material [31]. Furthermore, 3D applications are also useful in the planning of the most modern radio-surgical treatments, such as those carried out with the Cyberknife apparatus (Figure 11) [10,43]. Inflammatory Pathology
Neoplastic Pathology The diagnostic challenges related to the maxillofacial tumors, other than evaluation of the onset location, are
The primary inflammatory disease of maxillofacial bones is overall essentially rare. It consists of a few entities such as osteitis and osteonecrosis.
Figure 12. Odontogenic inflammation. Multiplanar reconstruction (MPR) image of the maxillofacial bones obtained along an oblique-coronal plane (A) shows an osteolytic area near the apex of 4.6, with cortical erosion of the mandible in its lingual side (arrow). MPR image, performed after i.v. contrast medium injection and obtained with soft tissue kernel (B), shows a voluminous abscess in the submandibular space (asterisk), enclosed cranially by the mylohyoid muscle (arrows) and sparing the sublingual space.
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The former may result from an odontogenic pathology or be an expression of complications of fracture lesions or surgery, while the necrosis may have iatrogenic causes, such as radionecrosis or the one induced in the maxillary bones by use of bisphosphonates [44]. In these cases, the 2dimensional multiplanar evaluation successfully aims at the identification of the original inflammatory outbreak and the definition of the extension of the inflammatory process to the adjacent spaces (Figure 12); the use of 3-dimensional reconstruction techniques is often unnecessary. Conclusions The knowledge of technical principles underlying the 3dimensional and multiplanar imaging is the prerequisite for a correct application of the reconstruction algorithms. In fact, the use of an incorrect or not sufficiently adequate reconstruction algorithm for the specific diseases (traumatic, malformative, neoplastic, inflammatory pathology), along with an improper setting of the reconstruction parameters, may result in a suboptimal quality of the diagnostic image. References [1] Flohr TG, Schaller S, Stierstorfer K, Bruder H, Ohnesorge BM, Schoepf UJ. Multi-detector row CT systems and image-reconstruction techniques. Radiology 2005;235:756e73. [2] Mazziotti S, Racchiusa S, Settineri N, Vinci S, Salamone I, Pandolfo I. Head and neck radiology: role of multidetector computed tomography in the evaluation of the tympanic canaliculus. Radiol Med 2011;116:657e66. [3] Vannier MW, Marsh JL, Warren JO. Three-dimensional CT reconstruction images for craniofacial surgical planning and evaluation. Radiology 1984;150:179e84. [4] Darlymple NC, Prasad SR, El-Merhi FM, Chintapalli KN. Price of isotropy in multi detector CT. Radiographics 2007;27:49e62. [5] Flohr T, Stierstorfer K, Bruder H, Simon J, Schaller S. New technical developments in multislice CTePart 1: Approaching isotropic resolution with sub-millimeter 16-slice scanning. Rofo 2002;174:839e45. [6] Perandini S, Faccioli N, Zaccarella A, Re TJ, Pozzi Mucelli R. The diagnostic contribution of CT volumetric rendering techniques in routine practice. Indian J Radiol Imaging 2010;20:92e7. [7] Choplin RH, Buckwalter KA, Rydberg J, Farber JM. CT with 3D rendering of the tendons of the foot and ankle: technique, normal anatomy and disease. Radiographics 2004;24:343e56. [8] Henrot P, Blum A, Toussaint B, Troufleau P, Stines J, Roland J. Dynamic maneuvers in local staging of head and neck malignancies with current imaging techniques: principles and clinical applications. Radiographics 2003;23:1201e13. [9] Weissman JL, Carrau RL. ‘‘Puffed-cheek’’ CT improves evaluation of the oral cavity. Am J Neuroradiol 2001;22:741e4. [10] Mazziotti S, Ascenti G, Scribano E, et al. CT-MR integrated diagnostic imaging of the oral cavity: neoplastic disease. Radiol Med 2013;118: 123e39. [11] Celebi I, Oz A, Sasani M, et al. Using dynamic maneuvers in the computed tomography/magnetic resonance assessment of lesions of the head and neck. Can Assoc Radiol J 2013;64:351e7. [12] De Filippo M, Onniboni M, Rusca M, Carbognani P, Ferrari L, Guazzi A. Adventages of multidetector-row CT with multiplanar reformation in guiding percutaneous lung biopsies. Radiol Med 2008; 113:945e53. [13] Mazziotti S, Arceri F, Vinci S, Salamone I, Racchiusa S, Pandolfo I. Role of coronal oblique reconstructions as a complement to CT study of the temporal bone: normal anatomy. Radiol Med 2006;111:607e17.
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