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Nuclear Medicine |
1 From the Departments of Radiology, Nuclear Medicine Service (H.S., H.W.D.Y., S.M.L.), Biostatistics (M.G.), and Surgery, Head and Neck Service (D.K.), Memorial Sloan-Kettering Cancer Center, Box 77, 1275 York Ave, New York, NY 10021. From the 2002 RSNA scientific assembly. Received February 18, 2003; revision requested May 2; final revision received July 10; accepted September 29. Address correspondence to H.S. (e-mail: schoderh@mskcc.org).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Studies of 68 patients were reviewed by two physicians in consensus. Focal fluorodeoxyglucose (FDG) uptake in the head and neck on attenuation-corrected PET images was graded as benign, equivocal, or malignant. CT and PET/CT images were then reviewed, and initial findings were amended if necessary. Comparison was performed on a lesion-by-lesion basis. Accuracy was evaluated on the basis of follow-up and histopathologic findings. Potential effects on patient care were assessed by a head and neck surgeon. PET and PET/CT accuracy was compared with a McNemar test adjusted for clustering.
RESULTS: A total of 157 foci with abnormal FDG uptake were noted, two of which were seen only on PET/CT images. PET/CT images were essential in determining the exact anatomic location for 100 lesions (74% better localization in regions previously treated surgically or with irradiation vs 58% in untreated areas; P = .06). On the basis of PET findings alone, 45 lesions were considered benign; 39, equivocal; and 71, malignant. With PET/CT, the fraction of equivocal lesions decreased by 53%, from 39 of 155 to 18 of 157 (P < .01). PET/CT had a higher accuracy of depicting cancer than did PET (96% vs 90%, P = .03). Six proved malignancies were missed with PET, but only one was missed with PET/CT. PET/CT findings altered the care for 12 (18%) of 68 patients.
CONCLUSION: PET/CT is more accurate than PET alone in the detection and anatomic localization of head and neck cancer and has the clear potential to affect patient care.
© RSNA, 2004
Index terms: Computed tomography (CT), 20.12111, 20.12115 • Dual-modality imaging, PET/CT • Head and neck neoplasms, 20.32, 20.33 • Images, fusion • Positron emission tomography (PET), 20.12163, 20.12166
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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After radiation and/or chemotherapy, changes in tumor metabolism precede morphologic changes. Similarly, after radical surgery or radiation therapy for head and neck malignancies, normal tissue planes are altered substantially. Therefore, CT and MR imaging have relatively poor specificity in the assessment of residual or recurrent disease following radical therapy (2–5). Positron emission tomography (PET), on the other hand, helps evaluate tumor metabolism, and the information obtained is essentially independent of tumor location and lesion size. For these reasons, PET with the glucose analogue fluorodeoxyglucose (FDG) has been used successfully for the assessment of tumor aggressiveness (6,7), for staging of nodal disease in the neck (8–10), for treatment evaluation (7,11), and for detection of recurrent disease (12–15) in patients with head and neck cancer. Unfortunately, the lack of anatomic detail remains a major limitation of PET as it is currently used.
Combined PET/CT is a recent imaging technique that permits almost synchronous image acquisition and exact co-registration of anatomic and metabolic data sets (16). Findings of initial studies have shown that this technique improves the anatomic localization of PET abnormalities and reduces the number of equivocal PET interpretations (17,18). Because of the complex anatomy in the head and neck region and because a number of normal structures (eg, lymphoid tissue, laryngeal muscle, and salivary glands) demonstrate a wide variety of patterns and intensity of FDG uptake, we expected that this technique might provide an advantage in the interpretation of PET images in patients with head and neck malignancies. The aim of this study was, therefore, to compare the diagnostic accuracy of attenuation-corrected PET images with that of PET/CT fused images in patients with head and neck cancer and to evaluate the effect of PET/CT findings on patient care.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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Patient Population
The PET/CT database was searched for names of patients with head and neck cancer who were imaged between November 2001 (time of PET/CT installation) and May 2002. The final study population consisted of 68 patients (Table 1). There were 44 male (mean age, 59 years ± 12 [SD]; age range, 38–80 years) and 24 female (mean age, 56 years ± 16; age range, 14–81 years) patients. The mean age for the entire study population was 58 years ± 13 (range, 14–81 years). Fifty-two patients had squamous cell carcinoma of the head and neck; eight patients had neck metastases of an unknown primary tumor; and eight patients had recurrent or metastatic follicular (n = 1), papillary (n = 4), or medullary (n = 3) thyroid carcinoma. Clinical indications for PET/CT included staging of newly diagnosed head and neck cancer (n = 16), detection of an unknown primary tumor (n = 8), evaluation of residual disease after chemotherapy or radiation therapy (n = 10), and clinically suspected recurrent disease (n = 34). Forty-four patients had undergone surgery or radiation therapy prior to PET/CT, with a mean interval of 8 months (range, 1–40 months). Details are shown in Table 1.
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After a 6-hour fasting period, patients were injected intravenously with 444–555 MBq (12–15 mCi) of FDG. After a 60-minute uptake period, during which patients were encouraged to rest, images were acquired. First, spiral CT was performed from the level of the middle of the skull to the level of the pelvic floor by using the following parameters: With the Biograph scanner, a scout view with 30 mA and 130 kVp, followed by a spiral CT scan with effective mA of 50, 130 kVp, 5-mm section width, 4-mm collimation, and a 12-mm table feed per rotation, were obtained; with the Discovery LS scanner, a scout view with 30 mA and 120 kVp, followed by a spiral CT scan with 0.8-second rotation time, 80 mA, 140 kVp, 5-mm section thickness, and a 4.25-mm interval in high-speed mode, were obtained. This was followed by acquisition of PET emission images (3–4 minutes per bed position of 11.2 [Biograph] or 14.2 cm [Discovery LS]). The total acquisition time varied between 25 and 35 minutes per patient. The CT data were used for attenuation correction of PET emission images.
Image Interpretation
All study findings were retrospectively interpreted jointly and in consensus by two experienced physicians (H.S., H.W.D.Y.) trained in diagnostic radiology and nuclear medicine (one physician had 7 years experience in CT and 9 years in PET, and the other physician had 5 years experience in CT and 9 years in PET). They were aware of the patients’ clinical history, which was provided by the referring physician, but were unaware of any results of other imaging studies if these were performed. Initially, only the attenuation-corrected PET images were reviewed in transaxial, coronal, and sagittal planes and as maximum intensity projections. Visual analysis was used, and lesions with abnormal FDG uptake were recorded. Abnormal FDG uptake was defined as radiotracer accumulation that was thought to be outside of the normal anatomic structures, such as normal laryngeal muscle activity, and of higher uptake than background activity in the neck or in the location of the normal anatomic structures but asymmetric and/or of higher intensity than is normally seen. Lesions with abnormal FDG uptake were graded as benign, equivocal, or malignant, and their likely anatomic location was recorded. Grading of lesions was based on the presumed anatomic location (eg, a likely benign FDG uptake in lymphoid tissues in nasopharynx or tonsils), as well as the symmetry and intensity of the radiotracer uptake.
Afterward, CT and PET/CT images were made available, and the initial findings (ie, grading of lesions and anatomic location) were amended if necessary.
PET/CT images were read directly from the screen of the computer workstation; other imaging studies were read from the picture archiving and communication system.
Evaluation of Accuracy and Statistical Analysis
The accuracy of PET and PET/CT image interpretation was assessed by using concurrent or subsequent imaging study findings (contrast material–enhanced CT, MR imaging, and ultrasonography; studies interpreted independently by staff radiologists who were not involved in this study), clinical examination findings, endoscopy findings, surgical findings, and histopathologic findings. PET/CT findings for which these data were available were classified as true-positive (presence of cancer), true-negative (absence of cancer), false-positive (increased FDG uptake unrelated to cancer), or false-negative (missed diagnosis of proved cancer). The following criteria were accepted as standard of reference: (a) histopathologic findings; (b) obvious clinical findings such as fungating carcinoma; (c) the combination of negative clinical findings, negative findings of other imaging studies, or negative follow-up findings; (d) resolution of apparent abnormalities at subsequent PET studies without intervening therapy together with negative clinical follow-up findings; and (e) the combination of positive clinical findings at the time of PET/CT and resolution of the tumor after chemotherapy or radiation therapy.
Since only abnormal images were included in the study, sensitivity and specificity were not calculated; instead, accuracy is presented in terms of the proportion of correctly classified lesions. PET and PET/CT images were compared in terms of accuracy by using the McNemar test adjusted for clustering (19,20). Since the primary objective was to provide estimates of diagnostic accuracy, patients’ clinical history was accessible to the readers. PET and PET/CT images were also compared in regard to the correct localization of lesions with abnormal FDG uptake, and improvements in anatomic localization on PET/CT images were noted. The number of lesions for which the fused images improved the anatomic localization was compared between previously treated (surgery or chemotherapy) and untreated regions by using the 
2 test, which was also adjusted for clustering. A P value of .05 was considered to indicate a statistically significant difference.
Effect on Patient Care
An attending head and neck surgeon (D.K.) independently reviewed clinical history, PET and PET/CT findings, and follow-up data. On the basis of his clinical judgment, the surgeon determined whether differences between PET alone and PET/CT were relevant for patient care. The number of patients in whom PET/CT findings would contribute to treatment decisions (in addition to clinical findings and findings of PET alone) was recorded.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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The original number of 39 equivocal lesions on PET/CT images decreased to 13, since 26 lesions could be reclassified as normal and/or benign (n = 21) or malignant (n = 5); details of this reclassification are shown in Figure 3. Examples of equivocal lesions on PET images that were reclassified as benign on PET/CT images included increased FDG uptake in skeletal muscles (eg, pterygoid, longus capitis, and constrictor pharyngis muscles) and joints, normal FDG uptake in lymphoid tissues, and posttreatment changes (Fig 4).
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When PET/CT fused images were used, the number of equivocal lesions decreased from 39 to 18 (56%, P < .01). This was associated with a simultaneous increase in the number of normal and/or benign lesions (from 45 to 63), as well as the number of lesions considered suspicious for malignancy (from 71 to 76). In 31 of the 33 lesions that were reclassified on the basis of PET/CT images, this reclassification was associated with—and oftentimes was largely caused by—the improved anatomic localization afforded by CT scans. In a number of cases, PET images revealed foci of increased FDG uptake, but CT scans did not demonstrate a corresponding abnormality; fused images (rather than a simple head-to-head comparison of the two image sets) were therefore essential for accurate study interpretation. Examples included increased FDG uptake in neck and mediastinal lymph nodes that did not meet size criteria for metastases, abnormal FDG uptake in bone or bone marrow without a corresponding CT abnormality, and localized abnormal FDG uptake in areas where CT revealed nonspecific posttreatment changes in the tongue or the pharyngeal wall. Overall, these changes in the grading of abnormal FDG uptake affected 25 (37%) of the 68 patients.
Follow-up and Diagnostic Accuracy
Follow-up data could be obtained for 131 (83%) of the 157 foci identified on PET/CT images; no follow-up data were available for 26 lesions. Results of the statistical analysis, therefore, refer to the 131 lesions for which follow-up data were available.
Histopathologic findings were available for 33 lesions. Clinical examination within 3 weeks of PET/CT provided straightforward findings for 16 lesions. For the remaining 82 lesions, follow-up data were available from clinical examination, endoscopy, or imaging studies (CT, MR imaging, PET), with a minimum interval of 3 months after PET/CT (mean, 22 weeks ± 7). Results are shown in Table 3.
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Four lesions were incorrectly classified as malignant with both PET and PET/CT because of their intensely increased FDG uptake (false-positive findings). These included one case of acute tonsillitis (tonsillectomy was performed in this patient with unknown primary tumor), one case of chronic inflammation in the hypopharynx after radiation therapy (confirmed at clinical follow-up), one case of residual intense FDG uptake in a neck lymph node after radiation therapy (later resolved without additional therapy), and one case of chronic ulceration of a tonsil related to boost radiation therapy (confirmed at histopathologic examination). Eighteen lesions had to be classified as equivocal even though PET/CT fusion was used, which we hoped would eliminate all uncertainties. Follow-up data were available for 11 of these lesions; eight were later found to be benign and two remained equivocal (one case of likely postsurgical and postradiation changes in the neck, with persistent increased FDG uptake in the neck without clear recurrence, and one case of inhomogeneous FDG uptake in several cervical vertebrae that may have been related to radiation therapy). One nonenlarged lymph node with mild FDG uptake was incorrectly reclassified as equivocal; however, histologic findings of the neck dissection specimen revealed malignant cells in this node.
Data for the 35 PET abnormalities that were reclassified on the basis of PET/CT images (n = 33) or were newly discovered with PET/CT only (n = 2) are shown in Table 4. In particular, histologic confirmation was available for six of the eight newly discovered malignant lesions; all were true-positive and included three nodal metastases, one partially necrotic carcinoma underneath a myocutaneous flap, and two tongue cancers.
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Effect of PET/CT on Patient Care
Changes in patient care that could be ascribed to the additional information provided by PET/CT images were noted for 17 lesions, affecting 18% (12 of 68 patients) of the population. Surgery was initiated in two cases (one recurrent tongue cancer and one laryngeal cancer), and the surgical approach was changed in a patient with medullary thyroid carcinoma in whom PET/CT images revealed a pretracheal nodal metastasis in a nonenlarged lymph node. In eight patients, concurrent follow-up imaging studies could be avoided because fused images permitted a clear interpretation of findings as benign (increased FDG uptake considered equivocal on PET images often requires further evaluation with other imaging studies or short-term follow-up). This was, for instance, noted for asymmetric skeletal muscle uptake of FDG, for inhomogeneously increased FDG uptake in myocutaneous flaps, and for increased FDG uptake related to postsurgical or postradiation changes in the head and neck. In one case, PET/CT images were essential for guiding a nodal biopsy of a lymph node in the upper anterior mediastinum (Fig 5). Findings of PET/CT-guided biopsy helped confirm recurrent nasopharyngeal carcinoma, and the patient proceeded to undergo chemotherapy followed by resection of the paratracheal nodes.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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FDG PET has become an accepted and widely used imaging modality for the staging and follow-up of head and neck cancer (8,9,13,14). In comparison with anatomic imaging modalities, PET is more accurate for the detection of neck nodal metastases (8,9) and recurrent disease (12–14), and it appears helpful for the detection of unknown primary tumors in patients with neck nodal metastases. In patients with recurrent head and neck cancer, FDG PET also has a prognostic value (13,21,22). Despite its proved clinical value, PET of the head and neck region shows focal radiotracer uptake that may or may not be abnormal, such uncertainties usually will lead to additional imaging studies (CT, MR imaging) or will require short-term follow-up. Even for the experienced physician, the lack of anatomic information on PET images poses a challenging task. This is particularly true for patients who have previously undergone surgery or radiation therapy, with subsequent alteration of normal tissues.
We therefore hypothesized, and were able to confirm in this study, that fusion of anatomic and metabolic data with PET/CT would improve the interpretation of PET images in patients with head and neck cancer. In planning this study, we decided to classify PET findings as benign, equivocal, or malignant. Although the classification of an imaging finding as equivocal is often not helpful for referring physicians and should be avoided whenever possible, this does reflect the actual clinical reporting style in our practice and likely also in many other institutions. Depending on the level of clinical suspicion, equivocal findings may require further evaluation with other imaging studies, biopsy, or clinical and imaging follow-up. This may be associated with additional costs for the health care system and an emotional burden for the patient involved. The significant decrease in the number of equivocal findings afforded by PET/CT fused images, associated with persistent high accuracy in image interpretation, is therefore of immediate clinical relevance. In this patient population, a clinically meaningful and correct diagnosis could be rendered for a substantially greater number of PET findings, affecting 37% of all patients. In particular, two findings considered benign and four findings considered equivocal with PET alone were correctly classified as cancer with PET/CT. The number of equivocal PET findings may appear surprisingly high at first glance. However, patients at this tertiary care hospital and cancer center often have complicated malignancies or an advanced-stage disease, and 63% of patients in this study had been pretreated with surgery or radiation therapy.
Despite our efforts, four lesions were incorrectly classified as malignant with both PET and PET/CT (false-positive findings). In each case, this was related to inflammation or posttreatment changes, a well-documented reason for false-positive FDG findings. We have found that regular close interaction between radiologists and referring surgeons is extremely valuable in reducing the number of false-positive interpretations and in improving the quality of PET and PET/CT reports. Nevertheless, a small number of false-positive findings are unavoidable, and depending on the level of clinical suspicion, these abnormal findings will have to be verified at histopathologic examination or clinical follow-up.
We did not use standardized uptake values for this retrospective analysis. Although standardized uptake values provide prognostic information and are helpful in the evaluation of the response to therapy, these numbers are of limited value in the detection of disease, in particular in pretreated patients. In some cases, standardized uptake values may be helpful in the characterization of lesions with increased FDG uptake, but when used in isolation they are not a useful tool in eliminating false-positive findings in FDG PET of the head and neck (13,23). For instance, the standardized uptake value does not provide any meaningful help in differentiating between tumor or metastases and a number of normal variants, including asymmetric skeletal muscle uptake, uptake in fat tissue in the neck (24), or intense FDG uptake in normal lymphoid tissue.
We would like to emphasize that PET/CT images had a clear effect on patient care in 18% of cases leading to changes in treatment approach, enabling earlier diagnosis of recurrent cancer, guiding biopsy, or eliminating the need for additional and follow-up imaging studies. Moreover, the imaging time can be shortened substantially by using PET/CT: Since CT data (rather than transmission images from a rod source) can be used for PET attenuation correction, an average whole-body PET study can be performed in 25–35 minutes rather than 45–60 minutes. The use of PET/CT in our patient population had therefore clear clinical and financial implications. For all of these reasons, we now routinely use PET/CT (rather than PET alone) in the evaluation of patients with head and neck cancer.
This was a retrospective study with all of its method-inherent limitations. Nevertheless, we believe that our data reflect daily clinical practice. Initially, the two interpreters were only given attenuation-corrected PET images and a maximum intensity projection but were aware of the clinical history and indication for performing the study (as provided by the referring physician). This certainly reflects the daily practice in most institutions. CT and fused images were then made available to evaluate whether PET/CT provided a clinically meaningful advantage over PET alone.
For each patient, PET images were interpreted first, followed by PET/CT images. Therefore, one might be concerned that a memory or interpretation bias could be present in this study. However, this approach reflects daily clinical practice (25). We acknowledge that in studies in which different independent imaging modalities (eg, CT vs MR imaging) are compared, the reading sequence is randomized to minimize the memory or sequence bias. However, PET/CT is not an independent imaging modality. Rather, the primary purpose of this new technology is to improve the PET interpretation with the additional structural information provided by the CT component. In fact, in the current study, all the information on a PET scan was readily available on a PET/CT scan because a PET/CT scan is indeed an overlay of an individual PET scan and an individual CT scan. Hence, a PET followed by PET/CT sequence does not introduce any bias. On the contrary, a PET/CT followed by PET sequence would have been prone to bias since interpretation of PET images would have possibly been confounded with the PET/CT image previously interpreted.
We did not attempt to compare PET images with a simultaneous display of PET and CT images alone. While it may be possible to improve the interpretation of PET findings by means of a simple visual comparison with CT images, we considered it more meaningful to take full advantage of the true benefit of this new technology—that is, PET/CT fusion imaging. In the past, several institutions have made an attempt to use conventional image fusion—that is, to use software programs and try to achieve co-registration of PET and CT image sets that were acquired at different times and with different equipment. We have realized that such attempts are frequently unsuccessful. In particular in the neck, where numerous anatomic structures are located in proximity, even slight misalignment between anatomic and PET image data can cause misinterpretation. In addition, many patients may present with CT or MR images obtained at an outside institution, so image fusion cannot be performed.
While it would have been ideal to have histopathologic results available in all cases, this is not usually the case in clinical practice, unless patient care depends on histologic verification of imaging findings. Since all PET/CT studies were ordered for specific clinical purposes, it is likely that the referring head and neck surgeons based their treatment decisions on these imaging results, at least to some degree. This could have created some verification bias; for instance, biopsy was performed only if PET/CT findings were suspicious for cancer. However, such potential bias was essentially unavoidable, given the retrospective nature of this study. We tried to address this concern by using a combination of other criteria as the standard of reference, which consisted of clinical follow-up, obvious clinical findings at the time of PET and PET/CT, other imaging studies that were interpreted independently by staff radiologists at our institution, and follow-up PET data. The combination of all of these data was not consistently available for all patients. However, the decision to obtain components of the reference standard, such as histopathologic results, was not based solely on PET/CT findings. A negative PET/CT image was considered true-negative only if there was enough supporting evidence (as explained in Materials and Methods), either clinical or from other imaging studies. While we cannot completely rule out the presence of a verification bias, it is likely to be of small magnitude.
Because of uncertainties regarding how intravenous contrast material may affect the CT data (and hence the quality and accuracy of the attenuation-corrected PET images), we did not use intravenous contrast material for this study. On the other hand, it is well known that intravenous contrast material substantially enhances the CT image quality in the neck and the accuracy of image interpretation (26). We therefore expect that in the future intravenous contrast material will be used, and perhaps routinely, for PET/CT studies in patients with head and neck cancer.
In comparison with standard PET, the use of combined PET/CT improved diagnostic accuracy and reduced the number of equivocal imaging findings in patients with head and neck cancer, leading to a change in patient care in 18% of cases. For these reasons, PET/CT fusion imaging is highly recommended in the evaluation of patients with head and neck malignancies.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, H.S.; study concepts and design, H.S., H.W.D.Y.; literature research, H.S.; clinical studies, H.S., H.W.D.Y.; data acquisition, H.S., H.W.D.Y.; data analysis/interpretation, H.S., M.G., H.W.D.Y., D.K.; statistical analysis, M.G.; manuscript preparation, H.S.; manuscript definition of intellectual content, H.S., H.W.D.Y.; manuscript editing, revision/review, and final version approval, all authors
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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S.-H. Ng, T.-C. Yen, C.-T. Liao, J. T.-C. Chang, S.-C. Chan, S.-F. Ko, H.-M. Wang, and H.-F. Wong 18F-FDG PET and CT/MRI in Oral Cavity Squamous Cell Carcinoma: A Prospective Study of 124 Patients with Histologic Correlation J. Nucl. Med., July 1, 2005; 46(7): 1136 - 1143. [Abstract] [Full Text] [PDF]
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T. Mau, Y. Oh, M. K. Bucci, and D. W. Eisele Management of Cervical Metastases in Advanced Squamous Cell Carcinoma of the Tonsillar Fossa Following Radiotherapy Arch Otolaryngol Head Neck Surg, July 1, 2005; 131(7): 600 - 604. [Abstract] [Full Text] [PDF]
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F. R. Miller, D. Hussey, M. Beeram, T. Eng, H. S. McGuff, and R. A. Otto Positron Emission Tomography in the Management of Unknown Primary Head and Neck Carcinoma Arch Otolaryngol Head Neck Surg, July 1, 2005; 131(7): 626 - 629. [Abstract] [Full Text] [PDF]
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B. F. Branstetter IV, T. M. Blodgett, L. A. Zimmer, C. H. Snyderman, J. T. Johnson, S. Raman, and C. C. Meltzer Head and Neck Malignancy: Is PET/CT More Accurate than PET or CT Alone? Radiology, May 1, 2005; 235(2): 580 - 586. [Abstract] [Full Text] [PDF]
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 G. J. Kelloff, J. M. Hoffman, B. Johnson, H. I. Scher, B. A. Siegel, E. Y. Cheng, B. D. Cheson, J. O'Shaughnessy, K. Z. Guyton, D. A. Mankoff, et al. Progress and Promise of FDG-PET Imaging for Cancer Patient Management and Oncologic Drug Development Clin. Cancer Res., April 15, 2005; 11(8): 2785 - 2808. [Abstract] [Full Text] [PDF]
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J.-H. Kim, J. Czernin, M. S. Allen-Auerbach, B. S. Halpern, B. J. Fueger, J. R. Hecht, O. Ratib, M. E. Phelps, and W. A. Weber Comparison Between 18F-FDG PET, In-Line PET/CT, and Software Fusion for Restaging of Recurrent Colorectal Cancer J. Nucl. Med., April 1, 2005; 46(4): 587 - 595. [Abstract] [Full Text] [PDF]
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 V. Kapoor, M. B. Fukui, and B. M. McCook Role of 18FFDG PET/CT in the Treatment of Head and Neck Cancers: Posttherapy Evaluation and Pitfalls Am. J. Roentgenol., February 1, 2005; 184(2): 589 - 597. [Full Text] [PDF]
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