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Role of ^18FFDG PET/CT in the Treatment of Head and Neck Cancers: Posttherapy Evaluation and Pitfalls

¹ Department of Radiology, Division of PET/CT Imaging, University of Pittsburgh Medical Center, Pittsburgh, PA 15213.
² Present address: 301 Frank Cushing Way, Suite 501, Tumon, GU 96913.
³ Department of Radiology, Allegheny General Hospital, Pittsburgh, PA 15213.

Received April 15, 2004; accepted after revision July 1, 2004.

 
Address correspondence to V. Kapoor (ajr{at}kapoorv.us).

Introduction

Top Introduction Posttherapy Evaluation of Head... Surveillance Recommendations Limitations Conclusion References

 
In the United States, extracranial head and neck carcinomas constitute 2–3% of cancers [1], whereas globally they represent 5.4% of all cancers (unpublished data from summary lecture notes, American Society of Head and Neck Radiology). Most head and neck cancers are squamous cell carcinomas of the larynx, nasopharynx, and oral cavity. Accurate initial staging of head and neck malignancies is critical in establishing the prognosis and in selecting the treatment for these patients. After treatment, the complex anatomy in this region is further complicated by postsurgical or radiation changes with the loss of the imaging landmarks and symmetry and with marked distortion of the normal anatomy, making the distinction between posttherapy changes and recurrence or residual tumor challenging. In these situations and in the detection of unknown primary tumors, distant metastases, and synchronous primary tumors, PET with ^18FFDG is a better imaging technique than either CT or MRI [2–5]. PET alone, however, has lower spatial resolution than CT or MRI. Fused PET/CT, described by Beyer et al. [6], combines the anatomic detail provided by CT with ^18FFDG PET metabolic information, thereby increasing accuracy in the detection of tumor [7].

This article addresses the role of ^18FFDG PET/CT in posttherapy evaluation of head and neck cancers, surveillance recommendations, limitations of this technique, and false-positive and false-negative results that may lead to erroneous interpretation.

Posttherapy Evaluation of Head and Neck Cancers on ^18FFDG PET/CT

Top Introduction Posttherapy Evaluation of Head... Surveillance Recommendations Limitations Conclusion References

 
The treatment paradigm for patients with head and neck cancers has shifted in the past 2 decades from a primarily surgical approach to a combination of therapies that includes surgery, preoperative or postoperative radiation therapy, and neoadjuvant or induction chemotherapy depending on the extent of disease and nodal status. Radiation therapy may be used as an adjunct to surgery for control of nodal disease or it may be used effectively as a primary treatment with or without chemotherapy [8, 9]. Surgery may be the preferred approach for patients with advanced nodal disease; however, in patients with N0 disease, prophylactic treatment with radiation therapy helps in controlling local disease and thus decreases the incidence of distant metastasis [10]. In patients with palpable nodal disease who respond completely to cisplatinum-based induction chemotherapy, local control may be achieved with high-dose radiation therapy, obviating radical neck surgery in some patients [10, 11].

In view of these expanding treatment options for head and neck cancer, imaging plays a vital role in initial staging and thus in guiding therapy. However, imaging has an even greater role in the detection of residual and recurrent head and neck tumors (Figs. 1A, 1B and 2A, 2B). PET with ^18FFDG has been shown to have greater accuracy than CT or MRI for restaging cancer and in assessing patients' response to chemotherapy and radiation therapy [12–14]. The sensitivity and specificity of ^18FFDG PET for detecting recurrent or residual disease are approximately 88–100% and 75–100%, respectively, compared with 70–92% and 50–57% of CT and MRI [14–17]. This superior accuracy of ^18FFDG PET compared with conventional imaging is based on detection by ^18FFDG PET of abnormalities in metabolism rather than abnormalities in anatomy, which can be greatly distorted after radiation or surgery (Figs. 3A, 3B, 3C, 3D and 4A, 4B, 4C, 4D, 4E). Surgical changes in the neck may be further complicated if patients have undergone some form of reconstructive procedure with grafts or flaps (free or pedicle). In patients with recurrent or residual disease, because of confusing surgical anatomy (Fig. 5A, 5B) and newly reconstructed tissues, areas of increased ^18FFDG uptake may be localized with greater confidence using fused ^18FFDG PET/CT than using either ^18FFDG PET alone or conventional cross-sectional imaging (Fig. 3A, 3B, 3C, 3D).

View larger version (118K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —63-year-old man with local recurrence of tongue carcinoma 6 months after resection with negative margins during initial surgery. IJV = internal jugular vein, CA = carotid artery. Axial contrast-enhanced CT image from 18FFDG PET/CT examination obtained at level of oral cavity shows mild asymmetry of soft tissues along floor of mouth, with increased soft tissue on left (arrowheads).

View larger version (80K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —63-year-old man with local recurrence of tongue carcinoma 6 months after resection with negative margins during initial surgery. IJV = internal jugular vein, CA = carotid artery. Fused 18FFDG PET/CT image obtained at same level as A shows marked increase in metabolic activity (arrows) that corresponds to soft tissue seen on CT image (A). Maximum standardized uptake value of 7.69 was suggestive of recurrent disease, which was confirmed at subsequent biopsy.

View larger version (86K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —60-year-old man with biopsy-proven retromolar trigone squamous cell carcinoma evaluated for staging and follow-up on 18FFDG PET/CT. Axial fused 18FFDG PET/CT image of oral cavity shows marked hypermetabolism in retromolar trigone (arrows) with maximum standardized uptake value of 11.04. No metastatic disease was identified, and patient underwent local resection of mass.

View larger version (92K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —60-year-old man with biopsy-proven retromolar trigone squamous cell carcinoma evaluated for staging and follow-up on 18FFDG PET/CT. Follow-up 18FFDG PET/CT image obtained 3 months after A shows postsurgical changes (arrowheads) with no abnormal 18FFDG uptake to suggest residual or recurrent tumor. IJV = internal jugular vein, T = physiologic 18FFDG uptake in lymphoid tissue at left tongue base.

View larger version (120K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —64-year-old man with locally recurrent squamous cell carcinoma of tongue 6 months following resection and radiation. IJV = internal jugular vein, M = mandible. Axial contrast-enhanced CT images of 18FFDG PET/CT at different levels of surgical site 6 months following resection and radiation show posttherapy changes with stranding in subcutaneous fat (arrowheads) and soft-tissue thickening (asterisks).

View larger version (128K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —64-year-old man with locally recurrent squamous cell carcinoma of tongue 6 months following resection and radiation. IJV = internal jugular vein, M = mandible. Axial contrast-enhanced CT images of 18FFDG PET/CT at different levels of surgical site 6 months following resection and radiation show posttherapy changes with stranding in subcutaneous fat (arrowheads) and soft-tissue thickening (asterisks).

View larger version (97K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C. —64-year-old man with locally recurrent squamous cell carcinoma of tongue 6 months following resection and radiation. IJV = internal jugular vein, M = mandible. Fused 18FFDG PET/CT images show focal hypermetabolism at only one site of soft-tissue thickening (arrow, C) without abnormal 18FFDG uptake at another site of soft-tissue thickening lower in neck (curved arrows, D). Biopsy confirmed recurrent tumor at site of abnormal 18FFDG uptake (arrow, C).

View larger version (110K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3D. —64-year-old man with locally recurrent squamous cell carcinoma of tongue 6 months following resection and radiation. IJV = internal jugular vein, M = mandible. Fused 18FFDG PET/CT images show focal hypermetabolism at only one site of soft-tissue thickening (arrow, C) without abnormal 18FFDG uptake at another site of soft-tissue thickening lower in neck (curved arrows, D). Biopsy confirmed recurrent tumor at site of abnormal 18FFDG uptake (arrow, C).

View larger version (84K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A. —60-year-old man with glottic squamous cell cancer who underwent long-term follow-up using 18FFDG PET/CT. Sagittal fused 18FFDG PET/CT image of neck obtained 1 year after patient underwent chemoradiation for glottic carcinoma shows focal supraglottic hypermetabolism extending into transglottic region (arrows) consistent with recurrent disease. Patient underwent total laryngectomy with selective neck dissection and pectoralis flap reconstruction.

View larger version (47K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B. —60-year-old man with glottic squamous cell cancer who underwent long-term follow-up using 18FFDG PET/CT. Axial fused 18FFDG PET/CT image of thorax obtained at same time as A shows enlarged anterior mediastinal lymph node (arrowhead) without abnormal 18FFDG uptake, suggestive of benign cause. Node remained unchanged on follow-up scans for 18 months. T = trachea, AA = ascending aorta.

View larger version (98K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4C. —60-year-old man with glottic squamous cell cancer who underwent long-term follow-up using 18FFDG PET/CT. Follow-up axial fused 18FFDG PET/CT of neck obtained 5 months after A and B shows increased 18FFDG uptake in left cervical lymph node (arrowhead). Standardized uptake value of 3.78 was suggestive of recurrent nodal disease, which was confirmed at subsequent biopsy. Patient underwent extended left radical neck dissection and brachytherapy.

View larger version (70K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4D. —60-year-old man with glottic squamous cell cancer who underwent long-term follow-up using 18FFDG PET/CT. Axial fused 18FFDG PET/CT image obtained at 6-month follow-up shows large focus of hypermetabolism (arrows) above tracheostomy stoma site that proved to be recurrent tumor at resection.

View larger version (108K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4E. —60-year-old man with glottic squamous cell cancer who underwent long-term follow-up using 18FFDG PET/CT. Axial fused 18FFDG PET/CT image obtained 4 months after D shows focally increased 18FFDG uptake along left skin flap (arrowheads) that was not seen on CT portion of examination (not shown). Biopsy of skin was positive for tumor. IJV = internal jugular vein, CA = carotid artery.

View larger version (118K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A. —58-year-old woman who underwent left partial glossectomy and nodal resection 4 years earlier for squamous cell carcinoma without evidence of recurrence on 18FFDG PET/CT. IJV = internal jugular vein. Axial contrast-enhanced CT image shows distortion of normal anatomy along right neck at prior surgical site (arrow) and minimal soft-tissue thickening (arrowhead).

View larger version (108K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B. —58-year-old woman who underwent left partial glossectomy and nodal resection 4 years earlier for squamous cell carcinoma without evidence of recurrence on 18FFDG PET/CT. IJV = internal jugular vein. No abnormal 18FFDG uptake suggestive of recurrence is seen on fused 18FFDG PET/CT image.

The technique of ^18FFDG PET/CT may also be used to assess response to initial high-dose radiation therapy or neoadjuvant chemotherapy. A progressive decrease in ^18FFDG uptake (Fig. 6A, 6B) correlates well with tumor regression [12, 18], whereas a lack of response or an increase in ^18FFDG uptake in a tumor may indicate a need to change therapy. Negative results obtained 4 months after completion of therapy are more reliable [13, 19, 20] than imaging findings obtained earlier. Use of earlier imaging findings may result in high false-negative rates. However, delaying imaging for a 4-month interval could mean that the window for salvage surgery may have passed [21].

View larger version (95K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6A. —45-year-old man with tonsillar mantle cell lymphoma who underwent 18FFDG PET/CT for assessing response to therapy. Axial fused 18FFDG PET/CT image obtained at level of oropharynx shows intense asymmetric hypermetabolism in left tonsil (arrowhead) that at biopsy proved to be primary tonsillar mantle cell lymphoma.

View larger version (89K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6B. —45-year-old man with tonsillar mantle cell lymphoma who underwent 18FFDG PET/CT for assessing response to therapy. Axial fused 18FFDG PET/CT image obtained 3 months after chemotherapy shows therapeutic response with decreased size of left tonsil (arrowhead) and no abnormal 18FFDG uptake.

Surveillance Recommendations

Top Introduction Posttherapy Evaluation of Head... Surveillance Recommendations Limitations Conclusion References

 
Current recommendations are that a base-line CT or MR image should be obtained in conjunction with clinical examination at 4–6 weeks after completion of therapy [9]. Although during this period ^18FFDG PET may have unacceptable rates of false-positive and false-negative results, it may be worthwhile obtaining an ^18FFDG PET/CT (instead of CT or MRI) image that could be used as a base-line for comparison with follow-up CT, PET, or fusion PET/CT images. Most deaths from head and neck cancers occur within 3 years of initial diagnosis, with the highest incidence of tumor recurrence (Fig. 4A, 4B, 4C, 4D, 4E) within 2 years of treatment [22, 23]. Therefore, clinical examination and imaging are recommended at 6-month intervals (4-month intervals for tumors with aggressive histology) for the first year and yearly thereafter for at least 2 years [9]. New mass, pain, vascular compromise, and neurologic deficit are indications for immediate clinical examination and imaging. Recommendations are that patients with advanced-stage disease and low clinical suspicion for recurrent tumor or with any stage of disease and moderate clinical suspicion of recurrent tumor undergo ^18FFDG PET as the initial investigation [24]. Because ^18FFDG PET has high sensitivity for recurrent disease [14–17], negative findings in such patients indicate that no further imaging is needed; however, if findings are positive, further cross-sectional imaging is advocated for assessing operative indications. Combined ^18FFDG PET/CT obviates additional imaging because recurrence and resectability can be assessed at the same time (Fig. 7A, 7B, 7C) in patients in whom the ^18FFDG portion of the study shows positive findings. Because MDCT is now available as the CT component of PET/CT, the CT portion of the examination may be used to diagnose other clinically relevant conditions that may need to be addressed before further therapy (Fig. 8A, 8B, 8C) and also is useful for excluding false-positive PET findings. Patients with a clinically evident lesion at follow-up examination need only CT or MRI to assess resectability. MRI is recommended as the initial investigation in patients with skull base, nasopharyngeal, or sinonasal cancers because of their propensity for perineural and intracranial spread [24] that may be difficult to assess with ^18FFDG PET/CT, given the high metabolic activity of the brain and beam-hardening artifact produced by the bones of the skull base on CT.

View larger version (104K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7A. —61-year-old man with recurrent esophageal adenocarcinoma 2 years after neoadjuvant chemotherapy and esophagectomy. Sagittal fused 18FFDG PET/CT image of upper thorax shows focal hypermetabolism at site of prior anastomosis (arrowhead) due to local recurrence. Aorta at level of tumor recurrence is narrowed focally (arrows), suggesting vascular encasement that makes lesion unresectable.

View larger version (90K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7B. —61-year-old man with recurrent esophageal adenocarcinoma 2 years after neoadjuvant chemotherapy and esophagectomy. Axial fused 18FFDG PET/CT image of oropharynx shows hypermetabolism at tongue base (arrows) and along gingival margins (arrowheads) due to chemotherapy-induced glossitis and gingivitis.

View larger version (78K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7C. —61-year-old man with recurrent esophageal adenocarcinoma 2 years after neoadjuvant chemotherapy and esophagectomy. Axial fused 18FFDG PET/CT image of lower neck shows hypermetabolic metastatic right supraclavicular lymph node (curved arrow). T = trachea, IJV = internal jugular vein.

View larger version (80K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 8A. —Images obtained in three patients show that CT portions of 18FFDG PET/CT examination can be used to diagnose diseases other than primary malignancy that may be important to patient treatment. In 52-year-old man who underwent 18FFDG PET/CT for evaluation of solitary pulmonary nodule, axial fused PET/CT image of chest shows type A aortic dissection (arrows) extending caudally into aortic root. Finding resulted in admission of patient to emergency department for urgent management of dissection.

View larger version (56K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 8B. —Images obtained in three patients show that CT portions of 18FFDG PET/CT examination can be used to diagnose diseases other than primary malignancy that may be important to patient treatment. In 49-year-old man with brain gliosarcoma undergoing 18FFDG PET/CT for evaluation of tumor recurrence, axial fused 18FFDG PET/CT image of chest shows extensive bilateral segmental pulmonary emboli (arrowheads) that would have been missed on isolated PET scan. AA = ascending aorta, PA = main pulmonary artery. Source: Kapoor V, McCook BM, Torok FS. An introduction to PET-CT imaging. RadioGraphics 2004;24:523-543. Reprinted with permission.

View larger version (105K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 8C. —Images obtained in three patients show that CT portions of 18FFDG PET/CT examination can be used to diagnose diseases other than primary malignancy that may be important to patient treatment. In 50-year-old man undergoing 18FFDG PET/CT for staging of Hodgkin's lymphoma, axial 18FFDG PET/CT image of brain shows aneurysm (arrow) in right middle cerebral artery. Intense physiologic metabolism of brain would have masked lesion on PET alone. Source: Kapoor V, McCook BM, Torok FS. An introduction to PET-CT imaging. RadioGraphics 2004;24:523-543. Reprinted with permission.

Limitations

Top Introduction Posttherapy Evaluation of Head... Surveillance Recommendations Limitations Conclusion References

 
False-negative results with ^18FFDG PET/CT may occur if a patient is scanned too early after completion of chemotherapy or radiation therapy if there is recurrent disease; if malignancy is present in structures with a physiologically elevated metabolism (e.g., tonsillar carcinoma); if tumor size is below the resolution of current PET/CT scanners (typically 10 mm for PET scanners); or if the tumor is not FDG-avid (Fig. 9A, 9B).

View larger version (80K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 9A. —55-year-old man with false-negative finding on 18FFDG PET/CT for metastatic tongue cancer to palpable right neck node. Axial fused 18FFDG PET/CT image obtained at level of mandible shows non-FDG-avid cystic mass (arrow) anteromedial to right sternocleidomastoid muscle, suggestive of congenital or benign cyst. Aspiration of cyst revealed atypical squamous cells. Arrowheads mark physiologic metabolism in genioglossus muscle. No abnormal uptake in right tongue was identified on this or other images. IJV = internal jugular vein, T = physiologic 18FFDG uptake in lymphoid tissue at left tongue base.

View larger version (99K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 9B. —55-year-old man with false-negative finding on 18FFDG PET/CT for metastatic tongue cancer to palpable right neck node. Coronal fused 18FFDG PET/CT image of neck shows physiologic uptake in palatine tonsils (straight arrows) and vocal cords (arrowheads). Curved arrow marks non-FDG-avid palpable cystic mass. Patient underwent bilateral tonsillectomies, multiple biopsies of tongue base, and right neck dissection that revealed poorly differentiated carcinoma of right tongue base that was metastatic to right cystic lymph node. Tonsils showed lymphoid hyperplasia without malignancy.

False-positive results may occur with ^18FFDG PET because of infections; physiologically increased uptake in structures such as palatine tonsils, salivary glands (salivary gland cancers are typically not FDG-avid), and masticator, oral cavity, neck, and laryngeal muscles (Figs. 10A, 10B and 11); uptake in reactive nonneoplastic lymph nodes; and, if within 4–6 months after surgery, noninfectious inflammation and granulation at the surgical site (flare phenomenon) (Figs. 12 and 13A, 13B, 13C). Uptake in muscles may be asymmetric and is usually due to anxiety with laryngeal and masticator activity after ^18FFDG injection. Coregistered images with ^18FFDG PET/CT allow direct correlation between ^18FFDG uptake and anatomic structures, thus reducing false-positive results. Standardized uptake values (SUVs) may be useful in distinguishing between malignant and benign ^18FFDG uptake. Although there is overlap between the ranges of SUVs that correspond to benign and malignant disease, an SUV of greater than 3 may be used as a general guide to indicate neoplasm. Sequential follow-up ^18FFDG PET/CT scans after surgery help in differentiating postoperative changes from tumor recurrence (Fig. 13A, 13B, 13C), and in some difficult cases, biopsy of ambiguous lesions visualized on ^18FFDG PET/CT may be needed to reach the correct diagnosis.

View larger version (93K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 10A. —64-year-old man with asymmetric vocal cord uptake on 18FFDG PET/CT due to large cell lung carcinoma invading aortopulmonary window. Axial fused 18FFDG PET/CT image of larynx shows asymmetrically greater 18FFDG uptake in right (normal) vocal cord (arrowheads) without metabolic activity in contralateral cord (arrow).

View larger version (77K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 10B. —64-year-old man with asymmetric vocal cord uptake on 18FFDG PET/CT due to large cell lung carcinoma invading aortopulmonary window. Coronal fused 18FFDG PET/CT image of chest shows large FDG-avid lung mass (curved arrow) extending into aortopulmonary window. Left vocal cord paralysis is due to involvement of left recurrent laryngeal nerve with asymmetric vocal cord metabolism. Also seen is encasement and marked attenuation of left pulmonary artery (straight arrow) by mass. Ao = aorta, T = trachea.

View larger version (91K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 11. —66-year-old man with asymmetric vocal cord activity. Axial 18FFDG PET/CT image of larynx shows asymmetric vocal cord metabolism with no 18FFDG uptake (arrow) in denervated and paralyzed left vocal cord. Cord damage resulted from transection of recurrent laryngeal nerve during resection of metastatic left thyroid nodule. Right vocal cord shows physiologic uptake.

View larger version (68K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 12. —54-year-old man treated for thyroid cancer with abnormal focal vocal cord activity. Axial 18FFDG PET/CT image of larynx shows asymmetrically increased 18FFDG uptake (arrow) in left vocal cord from granulation tissue after Teflon (polytetrafluoroethylene, DuPont) injection and thyroplasty. Procedure was performed to medialize paralyzed cord after thyroidectomy for thyroid carcinoma.

View larger version (64K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 13A. —57-year-old man with false-positive findings on 18FFDG PET/CT 5 weeks after neoadjuvant chemotherapy, radiation therapy, and total laryngectomy due to infection and fistula formation. Axial fused 18FFDG PET/CT images of neck show intense hypermetabolism (arrowheads, A and B) around surgical (A) and tracheostomy (B) sites. Arrow (A) marks cutaneous fistulous opening. Multiple biopsies during repair of fistula showed benign squamous mucosa and organizing granulation tissue without evidence of malignancy.

View larger version (77K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 13B. —57-year-old man with false-positive findings on 18FFDG PET/CT 5 weeks after neoadjuvant chemotherapy, radiation therapy, and total laryngectomy due to infection and fistula formation. Axial fused 18FFDG PET/CT images of neck show intense hypermetabolism (arrowheads, A and B) around surgical (A) and tracheostomy (B) sites. Arrow (A) marks cutaneous fistulous opening. Multiple biopsies during repair of fistula showed benign squamous mucosa and organizing granulation tissue without evidence of malignancy.

View larger version (99K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 13C. —57-year-old man with false-positive findings on 18FFDG PET/CT 5 weeks after neoadjuvant chemotherapy, radiation therapy, and total laryngectomy due to infection and fistula formation. Axial fused 18FFDG PET/CT image of neck obtained 1 year after A and B shows decreased metabolic activity at surgical site (arrowheads), confirming inflammation (rather than recurrence) as cause of increased 18FFDG uptake.

"Attenuation-correction" artifact (Fig. 14A, 14B, 14C, 14D) results from erroneous overcorrection of PET emission data by software that uses CT transmission data for attenuation correction. This occurs in areas that have a high attenuation on corresponding CT images (e.g., enhancing blood vessels, metallic implants) and can be easily detected by evaluating the uncorrected emission ^18FFDG PET data. Misregistration artifact from involuntary activity is not as much a problem in head and neck ^18FFDG PET/CT as in imaging the chest or abdomen. Adequate patient instruction and immobilization during scanning prevents artifact due to voluntary movements.

View larger version (88K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 14A. —"Attenuation-correction" artifact resulting from dense IV contrast material, dental hardware, and pacemaker in three patients. T = trachea. Attenuation-corrected axial fused 18FFDG PET/CT image of neck in 61-year-old man shows focus of hypermetabolism in left paratracheal region (arrow).

View larger version (91K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 14B. —"Attenuation-correction" artifact resulting from dense IV contrast material, dental hardware, and pacemaker in three patients. T = trachea. Non-attenuation-corrected fused 18FFDG PET/CT image obtained in 61-year-old man at same level as A shows no activity in intensely enhancing (high-attenuation) left internal jugular vein (arrowhead) on side of contrast injection.

View larger version (71K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 14C. —"Attenuation-correction" artifact resulting from dense IV contrast material, dental hardware, and pacemaker in three patients. T = trachea. Attenuation-corrected axial fused 18FFDG PET/CT images obtained in 37-year-old woman of mandible (C) and in neck of 66-year-old man (D) show apparent hypermetabolism due to high CT attenuation from dental hardware (straight arrows, C) and pacemaker (curved arrow, D). C = clavicle.

View larger version (83K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 14D. —"Attenuation-correction" artifact resulting from dense IV contrast material, dental hardware, and pacemaker in three patients. T = trachea. Attenuation-corrected axial fused 18FFDG PET/CT images obtained in 37-year-old woman of mandible (C) and in neck of 66-year-old man (D) show apparent hypermetabolism due to high CT attenuation from dental hardware (straight arrows, C) and pacemaker (curved arrow, D). C = clavicle.

Conclusion

Top Introduction Posttherapy Evaluation of Head... Surveillance Recommendations Limitations Conclusion References

 
During the early follow-up period after therapy, ^18FFDG PET may produce false-negative and false-positive results that may be decreased by using combined ^18FFDG PET/CT, which may also serve as a baseline study. The technique of ^18FFDG PET/CT is probably superior to both ^18FFDG PET and conventional cross-sectional imaging for assessing the presence of recurrent disease 6 months after completion of therapy and also helps in diagnosing other co-morbid conditions in these patients that may affect the clinical treatment.

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Top Introduction Posttherapy Evaluation of Head... Surveillance Recommendations Limitations Conclusion References

 

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