Head and Neck Normal Variations and Benign Findings in FDG Positron Emission Tomography/ Computed Tomography Imaging Liselotte Højgaard, MD, DMSCia,*, Anne Kiil Berthelsen, MDb, Annika Loft, MD, PhDb KEYWORDS Head and neck Positron emission tomography Computed tomography Imaging Physiologic uptake Benign tumors
KEY POINTS
INTRODUCTION
PET/CT SCANNING PROTOCOLS
The head and neck region is typically included in every whole-body 18F-fluro-deoxyglucose (18F-FDG) positron emission tomography (PET)/ computed tomography (CT) scan. The anatomy of the head and neck region is complicated, with many small structures close together and delicate structures. Interpretation of small lymph nodes and detection of small primary tumors are challenges. The high physiologic FDG uptake in various benign structures, especially in the head and neck area, increases the risk of misinterpretation, and it is therefore mandatory to have knowledge about the pitfalls. This article will guide the reader through these problems by discussing scanning procedures and normal findings as well as benign tumors with FDG PET/CT in the head and neck area.
It is recommended that PET/CT is performed with diagnostic quality CT, including intravenous contrast media and with PET and CT interpreted by experts in both modalities to secure the highest quality. Time and effort should be spent on protocols for acquisition and image reconstruction. In a clinical setting, the CT part with intravenous contrast media can be used for PET attenuation correction, because the contrast media induced artifacts are rare and easy to detect.1 In clinical trials, a standardized protocol including a noncontrast CT is often recommended, reducing the risk of measuring attenuationcaused false increased standardized uptake value (SUV) in relevant foci. The patient should be well prepared with sufficient information about preparations and scanning procedures. FDG uptake in brown fat is a common
Disclosures: None. a Department of Clinical Physiology, Nuclear Medicine & PET, Faculty of Health and Medical Sciences, Rigshospitalet, University of Copenhagen, KF 4011, Blegdamsvej 9, DK 2100, Copenhagen, Denmark; b Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet, University of Copenhagen, KF 4011, Blegdamsvej 9, DK 2100, Copenhagen, Denmark * Corresponding author. E-mail address: [email protected] PET Clin 9 (2014) 141–145 http://dx.doi.org/10.1016/j.cpet.2013.11.002 1556-8598/14/$ – see front matter Ó 2014 Elsevier Inc. All rights reserved.
pet.theclinics.com
Physiologic uptake and other benign findings on positron emission tomography (PET)/computed tomography (CT) with FDG for the head and neck increase the risk of misinterpretation. PET/CT should be performed with diagnostic quality CT, including intravenous contrast media and with PET and CT interpreted by experts in both modalities to secure the highest quality. Knowledge of the anatomy in the head and neck region as well as the medical history of the patient is crucial.
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finding in the head and neck area, especially in children and young adults, and especially during winter. Often the uptake is symmetric, but unilateral foci do occur. Fortunately, fat tissue is easily depicted on the CT scan. The fat tissue uptake can be reduced by letting the patient rest in a warm environment or tucked under warm blankets. In children this procedure is often sufficient. Adults can be prepared with a beta-blocking agent or muscle relaxing treatment (eg, diazepam) given 1 hour before the FDG injection followed by the same warm and comfortable rest period, although this procedure is still debatable.2–4
FDG Patients must be fasting at least 6 hours prior to FDG injection; children need 4 hours fasting. In patients with diabetes, it is important that they are scheduled early in the morning for the first scans, and that special diabetes protocols are followed. The recommended FDG dose is 4 MBq/kg body weight, maximum 500 MBq; children should receive 3 MBq/kg body weight until 16 years. Children older than 16 years should be dosed as adults.5 It is crucial that the patients are lying still and quietly between FDG injection and scan. Activated brown fat tissue in the head and neck area can be decreased or even completely avoided by pretreatment with beta-blocking agents or diazepam.
Radiation Doses Adults will receive approximately 5 mSv (0.019 mSv/MBq), and children will receive approximately 4 mSv5 due to the FDG injection. The radiation dose from a whole-body CT scan of diagnostic quality is approximately 10 mSv, but the new CT scanners with iterative reconstruction possibilities can reduce the dose even further. In children, the radiation dose is approximately 1 to 4 mSv from the CT scan. So in total, the adult radiation dose for an FDG PET/CT whole-body scan with diagnostic quality CT is approximately 15 mSv, and in children, the dose is 5 to 8 mSv.
Scanning Protocol For the diagnostic CT, it is important to have a meticulous preparation of both scan protocol and intravenous contrast media. The diagnostic CT parameters should be 80 to 120 mA, 120 to 140 kV, and 2 to 3 mm slice thickness. The patient should be positioned with the arms down and special immobilization devices for the head and neck area. It is recommended to give the intravenous contrast media with an automatic intravenous
pump. The delay must be set to show the contrast media in the head and neck region depending on the scanner characteristics. The reason for using intravenous contrast media in PET/CT is to discriminate the vessels from other structures more than to get enhancement in the tumor.
Patient Positioning The patient must be positioned comfortably to avoid motion during scanning and should prior to this be asked to remove metal in area of scanning (eg, jewelry, piercings, or metal in clothes).
Acquisition Protocol After the CT scan, the PET scan is performed, preferably in 3-dimensional mode, with an acquisition time of 2 to 4 minutes per bed position depending on the patient’s size and weight.
Image Reconstruction CT images are reconstructed with a 70 cm field of view (FOV) and a slice thickness of typically 2 mm. Attenuation and scatter-corrected PET data are reconstructed iteratively using a 3-dimensional attenuation weighted ordered subset expectation maximization (AW-OSEM) reconstruction including point spread function (PSF), and, if available, time of flight (TOF). The settings are 3 iterations, 21 subsets, and a 2 mm Gaussian filter. The images are reconstructed on a 336 336 or 400 400 matrix (scanner dependent) with a pixel size of 2 mm 2 mm and a slice thickness of 3 mm.
PET/CT IMAGE INTERPRETATION The quality of the PET/CT interpretation is increased, if it is done in collaboration with a specialist in nuclear medicine and a specialist in diagnostic radiology, and preferably done simultaneously. In some countries, physicians have competence in both nuclear medicine and radiology, and therefore can do the interpretation alone. However, 4 eyes see more than 2 eyes. Taking the overall costs of the PET/CT, including isotope, into account makes the costs of doublereading minor. Knowledge of the anatomy in the head and neck region (Fig. 1) as well as the medical history of the patient, especially prior surgery or radiotherapy in the relevant region, is of course crucial.
PHYSIOLOGIC FDG UPTAKE FDG is a glucose metabolism tracer; therefore physiologic uptake is seen in normal tissue as well as in malignant tumors. The degree of uptake
FDG PET/CT and Benign Findings in the Head & Neck Region
Fig. 3. High physiologic FDG uptake in the tonsils.
Fig. 1. Anatomy of the head and neck region. (From Edge SB, Byrd DR, Compton CC, et al, editors. AJCC cancer staging handbook. 6th edition. New York: Springer-Verlag; 2002. p. 29; with permission.)
(eg. measured as SUV) is not useful for discriminating between tissue types. Pattern recognition, especially with the underlying CT, is the only way to evaluate the images. The most common sites of physiologic uptake in the head and neck region are in the salivary glands, including the sublingual glands (Fig. 2). These structures are most often symmetric and easy to depict on the CT scan. The degree of uptake can vary. The excretion of FDG avid saliva in the oral cavity is sometimes not symmetric and tends to be high if the patient is dehydrated. The tonsils are always FDG avid (Fig. 3), and typically the uptake is symmetric. Individual variations occur, so a slight degree of asymmetry is not indicative of pathology.6–8 In children and adolescents, lymphoid tissue of Waldeyer ring is very
FDG avid; often the uptake pattern would be symmetric (Fig. 4).9 Uptake in muscular tissue is found due to contraction or previous exercise, but recent insulin injection or food intake will also give rise to high uptake. Typically this uptake is symmetric, but in case of surgery, irradiation, or muscle contraction, the pattern will be asymmetrical and much more difficult to interpret. In some areas like the paraspinal muscles, it is especially difficult (Fig. 5). Activity in the muscles of the tongue can be confusing, but the findings are often symmetric. Teeth grinding and chewing give rise to high muscular uptake in the mastication muscles. It is helpful to carefully examine the shape of the confusing FDG activity. Elongated shaped uptake is usually caused by physiologic uptake, whereas more focal activity tends to be pathologic. Again, the CT, especially with intravenous contrast, can be helpful in order to interpret the findings. The vocal cords in the larynx can be FDG avid in case of speaking during the FDG uptake time. Sometimes, the uptake is unilateral and can be
Fig. 2. (A) High FDG uptake in the parotid glands. (B) High FDG uptake in the submandibular glands.
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Højgaard et al one in the thyroid, a supplementary thyroid scintigraphy and/or ultrasound is recommended. Remember to postpone the thyroid scintigraphy for a minimum of 8 weeks if the PET/CT scan was performed with intravenous contrast, since the contrast contains iodine. Physiologic uptake in the spinal cord is typically higher at the cervical level but is recognized because of the diffuse distribution.
BENIGN FINDINGS
Fig. 4. FDG uptake in the lymphoid tissue of Waldeyer ring.
caused by vocal cord palsy with reduced uptake in the paralyzed cord and increased uptake in the normal cord, but the finding is not pathognomonic. Injection of calcium hydroxylapatite microspheres or other materials like Teflon used for treatment purposes can induce inflammation or even granulomatous reactions in the paralyzed cord.10 The shape of the cord on CT is helpful for interpretation, as the paralyzed cord would be relaxed and located in the middle of the larynx. It is important that the patient is relaxed before and during the FDG uptake period, and chewing gum should be avoided. Talking during FDG injection and uptake time should be kept at a minimum. Diffuse uptake in the thyroid gland can be a normal variant in euthyroid patients, but hyperthyroidism and chronic thyroiditis can also be the cause. Focal uptake in the thyroid due to benign adenomas is a common finding. As 30% or more of the foci are malignant, and CT can most often not discriminate a benign finding from a malignant
Fig. 5. Foci with high FDG uptake on the left side of the neck difficult to interpret on transaxial images.
Pleomorphic adenoma is a common benign salivary gland neoplasm characterized by neoplastic proliferation of parenchymatous glandular cells along with myoepithelial components, having a malignant potentiality. It is the most common type of salivary gland tumor and the most common tumor of the parotid gland. Warthin’s tumor is also seen often, the second most common benign parotid tumor (Fig. 6). The FDG uptake is high, and on CT, the tumor is hyperdense and contrast media enhanced but with a characteristic well defined appearance.10 Inflammation caused by radiation therapy or recent surgery may give rise to increased FDG uptake diffusely in the various tissues. This kind of uptake is seldom focal and does not give rise to interpretation difficulties. However, infection can induce high uptake and can be focal as in abscesses. Oppositely, reactive uptake in lymph nodes can be difficult to discriminate from malignant metastatic spread, and malignant tissue can give rise to reactive lymph nodes. The degree of FDG uptake is not very helpful, and CT does not add diagnostic information. A full medical history is always important, but crucial in these challenging patients.
Fig. 6. High FDG uptake in a Warthin tumor in the left parotid gland.
FDG PET/CT and Benign Findings in the Head & Neck Region REFERENCES
Fig. 7. Streak artifacts from teeth inducing falsepositive focus.
ARTIFACTS Artifacts in PET/CT are a well-known problem in whole-body examinations and should therefore be considered also in head and neck studies. Metal devices, especially dental implants, give rise to streak artifacts in CT, whether acquired at low doses or of diagnostic quality. In a combined PET/CT scanner, the CT data are used for attenuation correction, and the streak artifacts will therefore induce false-positive foci (Fig. 7). Beware of misalignment/misregistration of PET and CT images, as the head is more prone to motion than the rest of the body.
SUMMARY The head and neck area is a difficult region to interpret due to many physiologic and benign findings, and it is therefore important to be aware of the many possible pitfalls.
1. Berthelsen AK, Holm S, Loft A, et al. PET/CT with intravenous contrast media can be used for PET attenuation correction in cancer patients. Eur J Nucl Med Mol Imaging 2005;32:1167–75. 2. Tatsumi M, Engles JM, Ishimori T, et al. Intense (18) F-FDG uptake in brown fat can be reduced pharmacologically. J Nucl Med 2004;45:1189–93. 3. Barrington SF, Maisey MN. Skeletal muscle uptake of fluorine-18-FDG: effect of oral diazepam. J Nucl Med 1996;37:1127–9. 4. Sturkenboom MG, Hoekstra OS, Postema EJ, et al. A randomised controlled trial assessing the effect of oral diazepam on 18F-FDG uptake in the neck and upper chest region. Mol Imaging Biol 2009;11: 364–8. 5. Lassmann M, Biassoni L, Monsieurs M, et al. The new EANM paediatric dosage card. EANM Dosimetry and Paediatrics Committees. Eur J Nucl Med Mol Imaging 2008;35:1748. 6. Nakamoto Y, Tatsumi M, Hammoud D, et al. Normal FDG distribution patterns in the head and neck: PET/CT evaluation. Radiology 2005;234:879–85. 7. Bhargava P, Rahman S, Wendt J. Atlas of confounding factors in head and neck PET/CT imaging. Clin Nucl Med 2011;36:e20–9. 8. Blodgett TM, Fukui MB, Snyderman CH, et al. Combined PET-CT in the head and neck: part 1. Physiologic, altered physiologic, and artifactual FDG uptake [review]. Radiographics 2005;25:897–912. 9. Klijanienko J, Vielh P. Fine needle sampling of salivary gland lesions II. Cytology and histology correlation of 71 cases of Warthin’s tumor (adenolymphoma). Diagn Cytopathol 1997;16:221–5. 10. Halpern BS, Britz-Cunningham S, Kim CK. Intense focal F-18 FDG uptake in vocal cord associated with injection of calcium hydroxylapatite microspheres. Clin Nucl Med 2011;36:e175–7.
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KEY POINTS
INTRODUCTION
PET/CT SCANNING PROTOCOLS
The head and neck region is typically included in every whole-body 18F-fluro-deoxyglucose (18F-FDG) positron emission tomography (PET)/ computed tomography (CT) scan. The anatomy of the head and neck region is complicated, with many small structures close together and delicate structures. Interpretation of small lymph nodes and detection of small primary tumors are challenges. The high physiologic FDG uptake in various benign structures, especially in the head and neck area, increases the risk of misinterpretation, and it is therefore mandatory to have knowledge about the pitfalls. This article will guide the reader through these problems by discussing scanning procedures and normal findings as well as benign tumors with FDG PET/CT in the head and neck area.
It is recommended that PET/CT is performed with diagnostic quality CT, including intravenous contrast media and with PET and CT interpreted by experts in both modalities to secure the highest quality. Time and effort should be spent on protocols for acquisition and image reconstruction. In a clinical setting, the CT part with intravenous contrast media can be used for PET attenuation correction, because the contrast media induced artifacts are rare and easy to detect.1 In clinical trials, a standardized protocol including a noncontrast CT is often recommended, reducing the risk of measuring attenuationcaused false increased standardized uptake value (SUV) in relevant foci. The patient should be well prepared with sufficient information about preparations and scanning procedures. FDG uptake in brown fat is a common
Disclosures: None. a Department of Clinical Physiology, Nuclear Medicine & PET, Faculty of Health and Medical Sciences, Rigshospitalet, University of Copenhagen, KF 4011, Blegdamsvej 9, DK 2100, Copenhagen, Denmark; b Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet, University of Copenhagen, KF 4011, Blegdamsvej 9, DK 2100, Copenhagen, Denmark * Corresponding author. E-mail address: [email protected] PET Clin 9 (2014) 141–145 http://dx.doi.org/10.1016/j.cpet.2013.11.002 1556-8598/14/$ – see front matter Ó 2014 Elsevier Inc. All rights reserved.
pet.theclinics.com
Physiologic uptake and other benign findings on positron emission tomography (PET)/computed tomography (CT) with FDG for the head and neck increase the risk of misinterpretation. PET/CT should be performed with diagnostic quality CT, including intravenous contrast media and with PET and CT interpreted by experts in both modalities to secure the highest quality. Knowledge of the anatomy in the head and neck region as well as the medical history of the patient is crucial.
Højgaard et al
142
finding in the head and neck area, especially in children and young adults, and especially during winter. Often the uptake is symmetric, but unilateral foci do occur. Fortunately, fat tissue is easily depicted on the CT scan. The fat tissue uptake can be reduced by letting the patient rest in a warm environment or tucked under warm blankets. In children this procedure is often sufficient. Adults can be prepared with a beta-blocking agent or muscle relaxing treatment (eg, diazepam) given 1 hour before the FDG injection followed by the same warm and comfortable rest period, although this procedure is still debatable.2–4
FDG Patients must be fasting at least 6 hours prior to FDG injection; children need 4 hours fasting. In patients with diabetes, it is important that they are scheduled early in the morning for the first scans, and that special diabetes protocols are followed. The recommended FDG dose is 4 MBq/kg body weight, maximum 500 MBq; children should receive 3 MBq/kg body weight until 16 years. Children older than 16 years should be dosed as adults.5 It is crucial that the patients are lying still and quietly between FDG injection and scan. Activated brown fat tissue in the head and neck area can be decreased or even completely avoided by pretreatment with beta-blocking agents or diazepam.
Radiation Doses Adults will receive approximately 5 mSv (0.019 mSv/MBq), and children will receive approximately 4 mSv5 due to the FDG injection. The radiation dose from a whole-body CT scan of diagnostic quality is approximately 10 mSv, but the new CT scanners with iterative reconstruction possibilities can reduce the dose even further. In children, the radiation dose is approximately 1 to 4 mSv from the CT scan. So in total, the adult radiation dose for an FDG PET/CT whole-body scan with diagnostic quality CT is approximately 15 mSv, and in children, the dose is 5 to 8 mSv.
Scanning Protocol For the diagnostic CT, it is important to have a meticulous preparation of both scan protocol and intravenous contrast media. The diagnostic CT parameters should be 80 to 120 mA, 120 to 140 kV, and 2 to 3 mm slice thickness. The patient should be positioned with the arms down and special immobilization devices for the head and neck area. It is recommended to give the intravenous contrast media with an automatic intravenous
pump. The delay must be set to show the contrast media in the head and neck region depending on the scanner characteristics. The reason for using intravenous contrast media in PET/CT is to discriminate the vessels from other structures more than to get enhancement in the tumor.
Patient Positioning The patient must be positioned comfortably to avoid motion during scanning and should prior to this be asked to remove metal in area of scanning (eg, jewelry, piercings, or metal in clothes).
Acquisition Protocol After the CT scan, the PET scan is performed, preferably in 3-dimensional mode, with an acquisition time of 2 to 4 minutes per bed position depending on the patient’s size and weight.
Image Reconstruction CT images are reconstructed with a 70 cm field of view (FOV) and a slice thickness of typically 2 mm. Attenuation and scatter-corrected PET data are reconstructed iteratively using a 3-dimensional attenuation weighted ordered subset expectation maximization (AW-OSEM) reconstruction including point spread function (PSF), and, if available, time of flight (TOF). The settings are 3 iterations, 21 subsets, and a 2 mm Gaussian filter. The images are reconstructed on a 336 336 or 400 400 matrix (scanner dependent) with a pixel size of 2 mm 2 mm and a slice thickness of 3 mm.
PET/CT IMAGE INTERPRETATION The quality of the PET/CT interpretation is increased, if it is done in collaboration with a specialist in nuclear medicine and a specialist in diagnostic radiology, and preferably done simultaneously. In some countries, physicians have competence in both nuclear medicine and radiology, and therefore can do the interpretation alone. However, 4 eyes see more than 2 eyes. Taking the overall costs of the PET/CT, including isotope, into account makes the costs of doublereading minor. Knowledge of the anatomy in the head and neck region (Fig. 1) as well as the medical history of the patient, especially prior surgery or radiotherapy in the relevant region, is of course crucial.
PHYSIOLOGIC FDG UPTAKE FDG is a glucose metabolism tracer; therefore physiologic uptake is seen in normal tissue as well as in malignant tumors. The degree of uptake
FDG PET/CT and Benign Findings in the Head & Neck Region
Fig. 3. High physiologic FDG uptake in the tonsils.
Fig. 1. Anatomy of the head and neck region. (From Edge SB, Byrd DR, Compton CC, et al, editors. AJCC cancer staging handbook. 6th edition. New York: Springer-Verlag; 2002. p. 29; with permission.)
(eg. measured as SUV) is not useful for discriminating between tissue types. Pattern recognition, especially with the underlying CT, is the only way to evaluate the images. The most common sites of physiologic uptake in the head and neck region are in the salivary glands, including the sublingual glands (Fig. 2). These structures are most often symmetric and easy to depict on the CT scan. The degree of uptake can vary. The excretion of FDG avid saliva in the oral cavity is sometimes not symmetric and tends to be high if the patient is dehydrated. The tonsils are always FDG avid (Fig. 3), and typically the uptake is symmetric. Individual variations occur, so a slight degree of asymmetry is not indicative of pathology.6–8 In children and adolescents, lymphoid tissue of Waldeyer ring is very
FDG avid; often the uptake pattern would be symmetric (Fig. 4).9 Uptake in muscular tissue is found due to contraction or previous exercise, but recent insulin injection or food intake will also give rise to high uptake. Typically this uptake is symmetric, but in case of surgery, irradiation, or muscle contraction, the pattern will be asymmetrical and much more difficult to interpret. In some areas like the paraspinal muscles, it is especially difficult (Fig. 5). Activity in the muscles of the tongue can be confusing, but the findings are often symmetric. Teeth grinding and chewing give rise to high muscular uptake in the mastication muscles. It is helpful to carefully examine the shape of the confusing FDG activity. Elongated shaped uptake is usually caused by physiologic uptake, whereas more focal activity tends to be pathologic. Again, the CT, especially with intravenous contrast, can be helpful in order to interpret the findings. The vocal cords in the larynx can be FDG avid in case of speaking during the FDG uptake time. Sometimes, the uptake is unilateral and can be
Fig. 2. (A) High FDG uptake in the parotid glands. (B) High FDG uptake in the submandibular glands.
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Højgaard et al one in the thyroid, a supplementary thyroid scintigraphy and/or ultrasound is recommended. Remember to postpone the thyroid scintigraphy for a minimum of 8 weeks if the PET/CT scan was performed with intravenous contrast, since the contrast contains iodine. Physiologic uptake in the spinal cord is typically higher at the cervical level but is recognized because of the diffuse distribution.
BENIGN FINDINGS
Fig. 4. FDG uptake in the lymphoid tissue of Waldeyer ring.
caused by vocal cord palsy with reduced uptake in the paralyzed cord and increased uptake in the normal cord, but the finding is not pathognomonic. Injection of calcium hydroxylapatite microspheres or other materials like Teflon used for treatment purposes can induce inflammation or even granulomatous reactions in the paralyzed cord.10 The shape of the cord on CT is helpful for interpretation, as the paralyzed cord would be relaxed and located in the middle of the larynx. It is important that the patient is relaxed before and during the FDG uptake period, and chewing gum should be avoided. Talking during FDG injection and uptake time should be kept at a minimum. Diffuse uptake in the thyroid gland can be a normal variant in euthyroid patients, but hyperthyroidism and chronic thyroiditis can also be the cause. Focal uptake in the thyroid due to benign adenomas is a common finding. As 30% or more of the foci are malignant, and CT can most often not discriminate a benign finding from a malignant
Fig. 5. Foci with high FDG uptake on the left side of the neck difficult to interpret on transaxial images.
Pleomorphic adenoma is a common benign salivary gland neoplasm characterized by neoplastic proliferation of parenchymatous glandular cells along with myoepithelial components, having a malignant potentiality. It is the most common type of salivary gland tumor and the most common tumor of the parotid gland. Warthin’s tumor is also seen often, the second most common benign parotid tumor (Fig. 6). The FDG uptake is high, and on CT, the tumor is hyperdense and contrast media enhanced but with a characteristic well defined appearance.10 Inflammation caused by radiation therapy or recent surgery may give rise to increased FDG uptake diffusely in the various tissues. This kind of uptake is seldom focal and does not give rise to interpretation difficulties. However, infection can induce high uptake and can be focal as in abscesses. Oppositely, reactive uptake in lymph nodes can be difficult to discriminate from malignant metastatic spread, and malignant tissue can give rise to reactive lymph nodes. The degree of FDG uptake is not very helpful, and CT does not add diagnostic information. A full medical history is always important, but crucial in these challenging patients.
Fig. 6. High FDG uptake in a Warthin tumor in the left parotid gland.
FDG PET/CT and Benign Findings in the Head & Neck Region REFERENCES
Fig. 7. Streak artifacts from teeth inducing falsepositive focus.
ARTIFACTS Artifacts in PET/CT are a well-known problem in whole-body examinations and should therefore be considered also in head and neck studies. Metal devices, especially dental implants, give rise to streak artifacts in CT, whether acquired at low doses or of diagnostic quality. In a combined PET/CT scanner, the CT data are used for attenuation correction, and the streak artifacts will therefore induce false-positive foci (Fig. 7). Beware of misalignment/misregistration of PET and CT images, as the head is more prone to motion than the rest of the body.
SUMMARY The head and neck area is a difficult region to interpret due to many physiologic and benign findings, and it is therefore important to be aware of the many possible pitfalls.
1. Berthelsen AK, Holm S, Loft A, et al. PET/CT with intravenous contrast media can be used for PET attenuation correction in cancer patients. Eur J Nucl Med Mol Imaging 2005;32:1167–75. 2. Tatsumi M, Engles JM, Ishimori T, et al. Intense (18) F-FDG uptake in brown fat can be reduced pharmacologically. J Nucl Med 2004;45:1189–93. 3. Barrington SF, Maisey MN. Skeletal muscle uptake of fluorine-18-FDG: effect of oral diazepam. J Nucl Med 1996;37:1127–9. 4. Sturkenboom MG, Hoekstra OS, Postema EJ, et al. A randomised controlled trial assessing the effect of oral diazepam on 18F-FDG uptake in the neck and upper chest region. Mol Imaging Biol 2009;11: 364–8. 5. Lassmann M, Biassoni L, Monsieurs M, et al. The new EANM paediatric dosage card. EANM Dosimetry and Paediatrics Committees. Eur J Nucl Med Mol Imaging 2008;35:1748. 6. Nakamoto Y, Tatsumi M, Hammoud D, et al. Normal FDG distribution patterns in the head and neck: PET/CT evaluation. Radiology 2005;234:879–85. 7. Bhargava P, Rahman S, Wendt J. Atlas of confounding factors in head and neck PET/CT imaging. Clin Nucl Med 2011;36:e20–9. 8. Blodgett TM, Fukui MB, Snyderman CH, et al. Combined PET-CT in the head and neck: part 1. Physiologic, altered physiologic, and artifactual FDG uptake [review]. Radiographics 2005;25:897–912. 9. Klijanienko J, Vielh P. Fine needle sampling of salivary gland lesions II. Cytology and histology correlation of 71 cases of Warthin’s tumor (adenolymphoma). Diagn Cytopathol 1997;16:221–5. 10. Halpern BS, Britz-Cunningham S, Kim CK. Intense focal F-18 FDG uptake in vocal cord associated with injection of calcium hydroxylapatite microspheres. Clin Nucl Med 2011;36:e175–7.
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