J Oral Maxillofac 49:1ow1043,

Surg

1991

omputerized Digital Enh raniofacial ephalometric BARRY L. EPPLEY,

MD, DMD,* AND A. MICHAEL

SADOVE, MD-f

Application of digital radiologic imaging techniques to cephaiometric assessment of the craniofacial skeleton is presented. Digital-enhanced and standard cephalometric radiographs were compared by osseous and soft tissue landmark analysis. Although both radiographic methods exhibited comparable accuracy at identifying bony landmarks, digital enhancement was consistently superior at delineating soft tissue relationships.

Bigitai Imaging Technology

Cephalometric radiography is valuable in diagnosis and treatment of facial deformities, as well as in study of longitudinal craniofacial skeletal development.“’ Cephalometric analysis, however, is subject to error from multiple sources, which include obtaining the radiograph, landmark identification, and measurement.’ The greatest number of errors have been shown to occur in landmark identification, provided that careful technique is used in patient positioning and averaged values are used from multiple measurements. 3-5Thus, efforts to improve accuracy in landmark identification should be directed primarily toward improvement in image quality. When a complicated network of interdigitating craniofacial bones, sutures, and varying soft tissue densities are superimposed, the resultant conventional radiographic image typically contains indistinct lines and edges. In addition, because the eye is more sensitive to the relative intensity of hght rather than the absolute amount (Weber-Fechner law), it is understandable that soft tissue landmark identification in cephalometric radiographic tracings is difficult.

The technique of storing a radiograph in a computer memory has been viewed with enthusiasm.@ A benefit of such technology is that several thousand radiographs can be stored and retrieved from a. single disk. Of clinical importance is that more information is available on a digitized radiographic image than on a conventional radiograph because computer manipulation of the image permits adjustment of contrast, density, edge enhancement, and also permits enlargement without loss of image quality. A digital image of a radiograph is produced by creating a rectangular array of numbers representing gray values (or shades of color for color images) from the negative film image. The elements of this array are termed pixels, each of which may be represented by 1,024 shades of gray. As a comparison, a television set can display only approximately 256 shades of gray. By convention, the pixels are integers in the range of 0 to 1,024, with 0 representing black and I$24 representing white. The image display part of the computer system converts these numbers into a video picture. Image processing is related to the visual effects of performing mathematical operations ou these numbers. Early technology in digital imaging used a television camera’to obtain an an&g image directly from the radiograph. This analog image was subsequently digitized. This system results in image degradation because the limiting factor is the ,resolution capability of the television camera. An alternative method of obtaining a digital image is to divide a conventional radiograph into many pixels with a laser scanner. The laser scanning beam passes through each pixel and the amount of transmitted

Received from the Craniofacial Program, Plastic Surgery Section, James Whitcomb Riley Hospital for Children, Indiana University Medical Center, Indianapolis. * Fellow. t Director. Address correspondence to Dr Eppley: Craniofacial Program, Plastic Surgery Section, James Whitcomb Riley Hospital for Children, Indiana University Medical Center, 702 Bamhill Dr, Rm 2514, Indianapolis, IN 46202-5200. 0 1991 American

Association

of Oral and Maxillofacial

Sur-

geons 0278-2391/91/4910-0002$3.00/0

1038

light is detected. This is digitized and translated into a shade of gray in the final image. This method of digital image acquisition is cumbersome because a conventional radiograph must first be obtained. In addition, it is still limited by the narrow dynamic range of the radiographic film. More recently, digital radiographs have been obtained through computerized technology. This system uses conventional radiographic equipment but, instead of radiographic film, a detector imaging plate is placed in the holding cassette. The image plate stores the energy from the radiation as a latent image. This latent image is released, pixel by pixeI, in a digital format. The digital imaging plate has a wide dynamic range, and the processing system automatically compensates for exposure errors, thus producing a film of uniform density. The computerized digital radiographic system permits a wide range of processing methods to be independently applied to each image. One of the more useful techniques of this process involves modifications of image contrast and brightness. These modifications can be selectively used for a small region of the radiograph so that detail can be more easily perceived; eg, one might choose to have high contrast in the lighter areas of the image and less contrast in the darker areas. In addition, various structures can h,ave their edges enhanced, thereby imnroving their visibility. Edge enbancement, like contrast and brightness, can also be selectively applied to either darker or lighter areas or to the entire image. The amount of applied edge enhancement can also be varied. The net result of computerized digital imaging is that one can consistently acquire images of uniform density with selective enhancement of any particular structure within the image. icmtion to Cephalometry Owing to the complexity of the craniofacial skeleton and the conformations of the overlying soft tissue, structure identification is difficult in the twodimensional plane. The utility of computerized digital radiologic techniques lies in their ability to improve ‘image quality and’ readability. Not only are bony landmarks and outlines more identifiable, but soft tissues,are also more easily perceived (Figs 1 to 4). Such techniques offer the capability of moving beyond the conventional methods of craniofacial cephalometric assessment. Several reports have documented preliminary efforts in which this technology has been applied to cephaiometric films.‘,” I&king this technology to a computer program, in which landmarks are identified by individual move-

ments 5f a cmsor on a monitor,11’12 or by the computer itself, should improve the process of cephalometric measurement. In addition, the capability of overlapping images of the same patient at differing periods of growth on the same screen offers the opportunity to enhance the procurement and accuracy of longitudinal craniofacial development data. Although enhanced images are an obvious visual asset, whether this degree of resolution translates into improved accuracy of outline tracing, planning, and follow-up remains to be evaluated. Therefore, a comparative analysis between conventional and digital cephalometric radiography was undertaken. aterials amd Twenty pediatric cleft patients, aged 5 to 8 years, undergoing secondary revisional surgery ‘were chosen for radiographic study. Lateral cephalometric radiographs were obtained intraoperatively immediately before surgery, with head alignment standardized through a portable positioning device (Porta-Stat, Diamond Head Scientifics, Sterling Heights, MI) _*3 Radiographs were exposed with a GE (Milwaukee, WI) AMX portable machine for 1.5 ms at 78 kVp and 50 mA. Fuji CR 633 f%n (Fuji, Japan, 25.7 X 36.4 cm) was exposed and developed in a Phillips KR Processor (Phillips terns, Shelton, CT). This processing duces two images of the patlent on the same film, one standard and the other digitally enhanced (Pigs 1 to 4), using one radiation exposure. A cephdometric method of radiographic assessment, similar to a previous repok,14 was used for analysis. Acetaie paper uacings were done of the paired images of each patient for a number of standardized craniofacial hard and soft8 tissue points by a single investigator (BLE).14~“5 H four bard tissue measurements (SNA, ,SNB C,-C3 angle, C&r) and the five soft tissue ~~~at~~~sh~ps (G-Sn-Pg, Sn-Gn-@, Cm&n-Is, ‘b-Sn/Sn-i&e, SnStm”/Sn-Stmi;Me), All measure~m’ents were ,,recorded and subjected to statk&3l, malybis with Student’s t test forpaired SanipIes (P 2 85 significance level). Standard deviations and the d ratio were determined similarly.

The osseous landmarks were readily identifiable with both radiographic teohniques. In hard tissue analysis, no significant difference existed between the two techniques (Table 1). In softtissue visualization, portions of the profile were often incompletely seen on the conventional

FIGURE 1. Adjustment of image contrast and density through computerized digital technology-. results in imnroved claritv of multi&e overlapping skeletal structures. A, Conventional PA craniofacial radiograph; B, digitalized PA craniofacial image.

FIGURE 2. Edge enhancement of craniofacial image of Pierre-Robin infant after undergoing a lip-tongue adhesion procedure for compromised airway. Marked improvement in clarity of the lip and tongue as well as the anterior fontanelle, coronal sutures, and other craniofacial structures is evident. A, Conventional radiograph; B, digital image.

EPPLEY AND SADOVE

FIGURE 3.

Cephalometric

FIGURE 4. Cephalometric digital image.

radiograph of bilateral cleft lip and palate infant. A, Conventional

radiograph of an I-year-old girl with mandibular horizontal deficiency.

radiograph; B, digital image.

A, Conventional

radi&raph;

B,

DIGITAL CRANIOFACIA’L CEPHALOMETRY

Table I m Comparisw CB% Cephaiometrk

RacJiographiqAnMy+ of Warious Sofb a&k HarcbTissue!Mkdsurements apd W~a%kmsh~ Means Tissue

Standard

Hard SNA SNB C,-C, C& Soft G-Sn-Pg Sn-Gn-C Cm-Sn-Es G-+%/&-Me Sn-Stm,/ Stm,-Me * Critical &

b “II

Cm -Sn-Ls LS -ISn-Me Pg w h-C ~

FIGURE 5. Hard tissue;

Cephalometric soft tissue.

G-Sn-Pg

landmarks that were analyzed.

A,

B,

radiographs. In contrast, all digitally enhanced films had clearly visible soft tissue profiles, which were significantly more accurate than on conventional radiographs (Table 1). Discussion The importance of visualization of both hard and soft tissue structures in craniofacial analysis is well recognized. With most current cephalometric radiographic methods, however, the bony landmarks are usually easily seen, but often at the expense of the

Digital

19.3” 73.9 25.1” 0.71

78.9” 73.7 24.6” 0.73

15.9 90.7” 104.2” “1.05

13.7” 94.1” 100.4” 0.95

0.48

0.56

SD

t

Ratio*

0.67 0.34 0.83. 0.07

0.84 0.37 0.92 -O.Q7

2.6 3.1 3.6 0.1

3.1 -4.15 5.7 0.4

0.09

-0.21

for 19 df = 2.093.

soft tissue profile. 16,17 Although additional techniques have improved soft tissue visibility,” uniform identfication of structures throughout the radiographic image is inconsistent owing to the wide range of density differences between structures. Application of computerized digital enhancement to cephalometry produces images of superior visual quality. Although bard tissue landmark ident%cation is similar to that of conventional cephalometric radiography, the soft tissue profile is consistently identifiable, making soft tissue rela$onship determination more accurate, as demonstrated in this study. Such accuracy is important in documenting postoperative changes and longitudinal growth. Although the computerized digital radiographic technique is currently available only in large radiologic centers, its introduction to outpatient and office facilities may occur in the next decade with equipment size reduction, improved computerized technology, and acquisition cost reduction. The capabilities of rapid image storage and retrieval, review of images either separately or ConcErrently, and clear structural imaging with manipulati& potential makes digital enhancement an exciting advance in cephalometric radiography. References 1. Buschang PH, LaPalme L, Tanguay R, et al: The technical reliability of superimposition on cranial base and mandibular structures. Eur .I Qrthod 8:152, 1986 2. Precious IX, Miles DA: The lateral craniofacialcepbalometric radiograph. J Oral Maxillofac Surg 45:737, 1987 3. Mitgard J, Bjork G, Linder-Aronson S: Reproducibility of cephalometric landmarks and errors of measurement of cephalometric cranial distances. Angle Orthod 44:56,1974 4. Ahlqvist J, Eliasson S, Welander V: The effect-of projection errors in cephalometric length measurements. Eur J Orthod 8:141, 1986 5. Houston WJB, Maher RE, McElroy 14, et al: Sources of

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6. 7. 8.

9.

10.

11.

12.

error in measurements from cephalometric radiographs. Eur J Orthod 8: 149, 1986 Twogood RE, Sommer FG: Digital image processing. IEEE Tram Nucl Sci 29:1076, 1982 Alvarez RE, Cassel DM: Film-based digital x-rays. Diaan Imag 5:36, 1983 Sartor-is DJ, Sommer FG: Digital film processing: applications to the musculoskeletal system. Skel Radio1 14:274. 1984 Jackson PH, Dickson GC, Birnie DJ: Digital image processing of cephalometric radiographs: a preliminary report. Br J Orthod 121122, 1985 Levy-Mandel AD, Venetsanopoulos AN, Tsotsos JK: Knowledge-based landmarking of cephalograms. Comput Biomed Res 19:282, 309, 1986 BeGole EA: Software development for the management of cephalometric radiographic data. Comput Programs Biomed 11:212, 1981 Konchak PA, Koehler JA: A Pascal computer program for

13. 14.

15. 16.

17.

18.

digitizing lateral cephalometric radisographs. Am J Grthod 87:197, 1985 Spolyar IL: The Porta-Stat. J Chn Orthod 20:262, 1986 Butow K-W, Mullen WG, DeMuelenqere JJGG: Profilocephalometric analysis: a combination of the cephalophotometric and the architectural-structural craniofacial analyses. Int J Adult Orthod Orthog Surg 4:87:1989 Legan HL, Burstone CJ: Soft tissue cephalometric analysis for orthognathic surgery. J Oral Surg 38:744, 1980 Butte1 Kt Schow SR: Comparison of soft-tissue enhanced and conventional cephalometric radiographs. J Oral Maxillofac Surg 47:804, 1989 Kaugars GE, Fatouros P: Clinical comparison of conventional and rare earth screen-film systems for cephalometric analysis. Oral Surg 53:322, 1982 Freedman M, Matteson S: A collimator for reduced radiiation dose with improved visualization of soft tissues. Radiology 118:226, 1976

Computerized digital enhancement in craniofacial cephalometric radiography.

Application of digital radiologic imaging techniques to cephalometric assessment of the craniofacial skeleton is presented. Digital-enhanced and stand...
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