Functional-anatomical image fusion in neuroendocrine tumors

Nuclear medicine provides physiologic and functional data for normal and pathologic organs but often the clear definition of the sites of radiotracers' uptake are difficult. Radiological methods are able to identify structural changes in a detailed way, but do not give precise information on function of organs or pathologic lesions. The registration and fusion of nuclear medicine studies with structural information obtained by radiological exams allows the precise correlation of functional and anatomical data. Software-based fusion of independently performed nuclear medicine and morphologic studies is uncertain of success and the alignment procedures are labor intensive. Recently, a new imaging device combining a dual-head, variable angle gamma camera with a low-dose x-ray tube has been introduced; the acquired single-photon emission computed tomography (SPECT) and x-ray computed tomography (CT) images are coregistered by means of the hardware in the same session. This new technology can be particularly useful when applied to scintigraphic procedures in neuroendocrine tumors. In-111 pentetreotide and radiolabeled MIBG play an important role in the study of patients with these tumors; the addition of anatomical maps provides a precise localization of SPECT findings and allows the exclusion of disease in sites of physiologic tracer uptake. SPECT/CT fused images are able to provide additional information that improves the accuracy of SPECT interpretation and leads to changes in therapeutic options, so enhancing the clinical role of nuclear medicine in evaluating patients with neuroendocrine tumors.     

Hybrid Imaging in Oncology

In oncology various imaging modalities play a crucial role in diagnosis, staging, restaging, treatment monitoringand follow up of various cancers. Stand-alone morphological imaging like computerized tomography (CT) andmagnetic resonance imaging (MRI) provide a high magnitude of anatomical details about the tumor but arerelatively dumb about tumor physiology. Stand-alone functional imaging like positron emission tomography(PET) and single photon emission tomography (SPECT) are rich in functional information but provide littleinsight into tumor morphology. Introduction of first hybrid modality PET/CT is the one of the most successfulstories of current century which has revolutionized patient care in oncology due to its high diagnostic accuracy.Spurred on by this success, more hybrid imaging modalities like SPECT/CT and PET/MR were introduced. Itis the time to explore the potential applications of the existing hybrid modalities, developing and implementingstandardized imaging protocols and train users in nuclear medicine and radiology. In this review we discussthree existing hybrid modalities with emphasis on their technical aspects and clinical applications in oncology.     

131I-meta-iodobenzylguanidine in diagnosis and treatment of neuroblastoma

131I MIBG is taken up and stored by neural crest tumors, essentially pheochromocytoma and neuroblastoma. MIBG diagnosis in neuroblastoma has been attempted with the following results. 205 total body scintigrams were performed in 60 patients with neuroblastoma with doses of MIBG ranging from 0.5 to 1 mCi. 52 were positive, 6 in complete remission were negative, and 2 were false negatives in adults with tumors showing no secretion of metabolites. More than 90% of neuroblastoma are MIBG positive, and therefore MIBG imaging is now considered the most valuable means of diagnosis and staging of these tumors. 131I MIBG therapy has been attempted in 22 patients with neuroblastoma. They received multiple therapeutic doses of 41 to 2,090 mCi given IV at 3- to 6-week intervals. The results were 5 complete remissions, 10 partial remissions, 1 no change, 2 progressive disease and 1 lost to FU. Apart from bone marrow depression in patients with previous bone marrow involvement, the treatment was well tolerated. Six adults with other neural crest tumors were also treated. Pain relief in metastatic patients is a common and important result of MIBG therapy.     

In vivo imaging and quantitation of adoptively transferred human antigen-specific T cells transduced to express a human norepinephrine transporter gene

Sequential imaging of genetically marked effector cells after adoptive transfer in vivo has greatly enhanced analyses of their biodistribution, growth, and activity both in animal models and in clinical trials of cellular immunotherapy. However, the immunogenicity of cells expressing xenogeneic reporter constructs limits their survival and clinical utility. To address this limitation, we have evaluated a human norepinephrine transporter (hNET) permitting imaging of transduced cells in vivo with a previously approved clinical grade radiolabeled probe, metaiodobenzylguanidine (MIBG). The hNET gene cDNA was cloned from the SK-N-SH cell line and inserted into a bicistronic retroviral vector also encoding green fluorescent protein. Following transfection, human EBV-specific T lymphocytes seemed fully functional in vitro and also selectively accumulated [(123)I]MIBG. In nonobese diabetic/severe combined immunodeficient mice bearing human EBV lymphoma xenografts, as few as 10(4) transduced T cells injected into the tumors could be imaged by single-photon emission computed tomography (SPECT) or positron emission tomography (PET) after i.v. infusion of [(123)I]MIBG or [(124)I]MIBG, respectively. When hNET(+) EBV-specific T cells were infused i.v., their migration and specific accumulation in EBV(+) tumors expressing their restricting HLA allele could be imaged by SPECT or PET over 28 days. Image intensity was closely correlated with the number of T cells accumulated in targeted tumors. The use of two reporter probes (MIBG and 2'-deoxy-2'-fluoro-beta-d-arabinofuranosyl-5-iodouracil) permitted independent contemporaneous tracking of two distinct EBV-specific T-cell subpopulations expressing different reporter genes (hNET-CD4(+) T cells and HSV-TK-CD8(+) T cells) in the same animal using three-dimensional nuclear modalities (SPECT and PET). The hNET-based system described may thus have significant potential as a nonimmunogenic reporter for extended repeated quantitative in vivo imaging of transduced cells in man.     

Utility of radiolabeled somatostatin receptor analogues for staging/restaging and treatment of somatostatin receptor-positive pediatric tumors

In this paper, we review the pediatric oncologic applications of somatostatin receptor-targeted imaging and therapy. Somatostatin receptors are expressed in high densities by embryonal tumors, such as neuroblastoma and medulloblastoma, and neuroendocrine tumors like carcinoids and islet cell tumors. We first review the distribution of these receptors in normal tissues and tumor cells. We then discuss the technique of somatostatin receptor scintigraphy (SRS) in the pediatric population. Next, the specific clinical applications of SRS with regard to the imaging of neuroblastoma, central nervous system tumors, and gastroenteropancreatic neuroendocrine tumors of childhood are discussed. Finally, we discuss the potential role of somatostatin receptor-targeted radiotherapy for improving the duration and quality of life of children with these tumors.     

PET/CT in pediatric oncology

Radionuclide functional imaging has become a central part of pediatric oncological practice. There have been a number of major advances in imaging technology in recent years, but multislice CT with PET is the modality generating most interest in cancer imaging. In this review, we discuss the common uses and specific issues with regard to PET-CT imaging in pediatric practice. Brain tumors form a significant percentage of pediatric oncology. Use of FDG-PET in brain tumors has helped distinguish viable, residual, or recurrent tumor from post-therapeutic changes and necrosis. High-grade tumors show high uptake of FDG at diagnosis. FDG-PET results may also not accurately correlate with tumor progression after intensive radiation therapy. FDG-PET has been applied to accurate biopsy of infiltrative tumors, tumor grading, and prognostication. Limited available data also suggest that FDG-PET findings correlate well with histopathology and clinical outcome in children. FDG uptake is generally greater in higher grade lymphomas than in lower grade lymphomas. FDG-PET reveals disease sites that are not detected by conventional staging methods, resulting in upstaging of disease with potential therapeutic review. FDG-PET is useful for assessing need for marrow biopsy, residual or recurrent soft tissue masses seen on CT after therapy. The primary role of FDG-PET in neuroblastoma is in non-MIBG concentrating tumors. [11C]-Hydroxyephedrine ([11C]-HED), an analogue of norepinephrine, and [11C]-epinephrine PET have also been used in evaluating neuroblastoma. Uptake of these tracers is demonstrated within minutes after tracer administration, an advantage over MIBG imaging. The exact roles of FDG-PET in osteosarcoma and Ewing's sarcoma are not definitive. FDG-PET may play an important role in monitoring response to therapy Another diagnostic role may be in assessing patients with suspected metastatic disease.     

Fusion imaging in nuclear medicine--applications of dual-modality systems in oncology

Medical imaging has become of the utmost importance in evaluating patients with cancer. Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) are accurate methods for detecting cancer and related metabolic abnormalities, but they often do not provide the anatomical landmarks needed to precisely localize lesions. Magnetic resonance imaging (MRI) and computed tomography (CT) scan, on the other hand, offer excellent anatomic detail but are less sensitive because they do not provide functional detail. Fusion imaging combines functional studies with morphological ones, so overcoming the drawbacks of both modalities. Software-based fusion of independently performed scintigraphic and radiological images has proven time consuming and impractical for routine use. Recently, dual-modality integrated imaging systems (SPECT/CT and PET/CT) have been developed: the acquired images are coregistered by means of the hardware in the same session. These new devices can be particularly useful for tumour imaging. The anatomical images provide precise localization and allow the exclusion of disease in sites of physiologic tracers' accumulation for SPECT and PET findings. Hybrid imaging in oncological applications has been very encouraging, indicating that these systems are suited for routine use in clinical practice. In fact, fused images provide additional information that improves diagnostic accuracy and impacts on patient management.     

Role of adrenal imaging in surgical management

Adrenal imaging using radiopharmaceuticals is a functional test that can contribute significantly to surgical management and follow-up of patients with either benign or malignant conditions of the adrenal cortex and medulla. Imaging of the cortex is achieved by iodine-131-labeled iodomethyl nor-cholesterol (NP-59), while adrenal medulla imaging can be successfully accomplished by 131I-metaiodobenzylguanidine (MIBG), which localizes in the adrenergic nerve terminal with norepinephrine. Both tests carry high sensitivity and specificity for functional tumors and hyperplasia, and often better than CT scanning. This article reviews the current status and clinical utility of nuclear imaging of the adrenal cortex in congenital hyperplasia, low renin hypertension and aldosteronism, and Cushing's syndrome. Adrenal medulla imaging is reviewed in light of our experience at the University of Texas M.D. Anderson Cancer Center in pheochromocytoma, neuroblastoma, and other neuroectodermal tumors. Investigation of 131I-MIBG therapy of metastatic tumors of neuroectodermal origin potentially offers a means of at least controlling symptoms of hormonal secretion in these patients.     

Application of PET/CT in the development of novel anticancer drugs

Combined positron emission tomography/computed tomography (PET/CT) is a relatively new imaging modality, combining the functional images of PET with the anatomical information of CT. Since its commercial introduction about 5 years ago, PET/CT has become an important tool in oncology. Currently, the technique is used for primary staging and restaging of cancer patients, as well as for surgery and radiation therapy planning. The abilities of PET/CT to measure early treatment response as well as drug distribution within the body make this technique very useful in the development of novel anticancer drugs. In this paper, the recent literature on the current role of PET/CT in drug development is reviewed.     

SPECT骨显像联合CT和MRI在恶性肿瘤骨转移诊断中的临床价值

目的探讨单光子发射计算机断层成像术(SPECT)骨显像联合CT和MRI在恶性肿瘤骨转移诊断中的应用价值。方法选取2016年3月至2019年3月间北京市房山区第一医院收治的80例恶性肿瘤并发骨转移患者,均采用SPECT骨显像、CT和MRI检查,分析原发肿瘤骨转移灶区域分布及三种检测方式诊断骨转移瘤的效能。结果无明显骨痛症状者46例,有明显骨痛症状者34例。骨转移瘤发生部位依次为脊柱、肋骨、骨盆、胸部、四肢和颅骨。脊柱转移瘤中,好发部位依次为胸椎、腰椎、骶椎和颈椎。SPECT与CT相同扫描野内诊断出464处病灶,SPECT检出429处(92.5%),CT检出率361处(77.8%),两者比较,差异有统计学意义(P<0.05),在相同扫描野之外SPECT另检出143处病灶。SPECT与MRI相同扫描野内诊断出321处病灶,SPECT检出307处(95.6%),MRI检出265处(82.6%),两者比较,差异有统计学意义(P<0.05),在相同扫描野之外SPECT另检出286处病灶。CT与MRI相同扫描野内诊断出259处病灶,CT检出185处(71.4%),MRI检出248处(95.8%),两者比较,差异有统计学意义(P<0.05)。SPECT骨显像联合CT和MRI检查的灵敏度、特异性和准确度均高于单独使用SPECT骨显像、CT或MRI,差异均有统计学意义(均P<0.05)。结论SPECT可作为可疑骨转移瘤的首选筛查手段,联合CT和MRI能明确恶性肿瘤骨转移的区域分布情况,提高诊断的灵敏度、特异性及准确度,有较高的临床价值。     

Utilisation de l’imagerie multimodalité en radiothérapie

The quality of treatment that one can realize today in conformai radiotherapy, can be reached only if one has access to 3D imaging allowing a precise determination of the volume of the organs at risk and of the GTV. For this reason, one has access to anatomical imaging, CT or MRI, and functional and metabolic imaging, PET or SPECT imaging. CT gives the electronic density of the tissus, which is essential to ensure a very precise calculation of dose distribution. Its insufficiency in the visualization of the tumor and some anatomical structures makes necessary the registration of these images with MRI of which distorsions are sufficiently weak to be usable in radiotherapy. The registration will be usable only if images of each modality are realized with the patient in treatment position, except for brain, where only CT, on which is based the registration, must be done in treatment position. At least, if one wants to visualize the active parts of a tumor or to make the difference between fibrosis and tumor left or recurrence after radiotherapy or chemetherapy, it is necessary to use PET or SPECT. To define correctly the CTV using these images, one must realize the anatomical localization of the metabolic abnormalities, which they highlight with a registration based on CT or MRI. The difficulties to obtain the registration of these images led the manufacturer to propose mixed machines allowing to realize, at the same time, a CT imaging and a PET or a SPECT imaging with the patient in treatment position.     

Surgical treatment of non-functioning pancreatic islet cell tumors

Pancreatic endocrine tumors (PETs) are rare neoplasms originating from the amine precursor uptake and decarboxylation (APUD) stem cells. Although the majority of PETs are sporadic, they frequently occur in familial syndromes. PETs may cause a variety of functional syndromes or symptoms of local progression if they are non-functional. General neuroendocrine tumor markers are highly sensitive in the diagnostic assessment of a PET. Imaging studies for tumor localization and staging include computer tomography (CT) scan, magnetic resonance imaging (MRI), In(111)-octreotide scan, MIBG, and endoscopic ultrasonography (EUS). Treatment of PETs often requires a multi-modality approach; however, surgical resection remains the only curative therapy for localized (non-metastatic) disease. Treatment of metastatic disease includes biologic agents, cytotoxic chemotherapy, and liver-directed therapies.     

Szintigraphie und Single-Photon-Emissions-Computertomographie (SPECT und PET)

Planar scintigraphy and single photon emission computed tomography (SPECT) or SPECT/computed tomography (CT) still play an important role in oncology, particularly in the detection of skeletal metastases, in thyroid cancer, in neuroendocrine tumours, and for imaging of the lymphatic system involved in drainage of the tumour area. Positron emission tomography (PET) or PET/CT has become an established modality in the management of many tumours. By far, the glucose analogue fluorodeoxyglucose (FDG) is the most frequently used radiotracer, used mainly for staging and detection of recurrences. Because inflammatory processes may be associated with increased glucose utilisation, bioptic confirmation of PET-positive findings may be required. For less dedifferentiated tumours, non-FDG PET tracers are increasingly employed, such as for prostate cancer and neuroendocrine tumours.     

Meta-[131I]iodobenzylguanidine uptake andmeta-[211At]astatobenzylguanidine treatment in human medulloblastoma cell lines

Summary Uptake of radioiodinated mefa-iodobenzylguanidine (MIBG) has been demonstrated in the neural crest tumors, including neuroblastoma, pheochromocytoma, and carcinoid tumors, and is presently in use diagnostically and therapeutically in these settings. Cells comprising medulloblastoma, the most common central nervous system malignancy in childhood, may be derived from a common germinal neuroepithelial cell as neural crest tissue, and as a result, also may have the capacity for accumulating MIBG. To investigate this hypothesis, we measured thein vitro binding of [¹³¹I]MIBG to 9 medulloblastoma-derived cell lines and the SK-N-SH neuroblastoma line known to accumulate MIBG. Seven of the medulloblastoma lines exhibited MIBG binding. The cell line with the greatest uptake, D384 Med, bound 11.2 ± 0.9% of added [¹³¹I]MIBG activity compared with 47.1 ± 2.3% for the SK-N-SH cell line. When 2 of the cell lines, D384 Med and D458 Med, were treated with the a-particle emitting analogue meta-[²¹¹At]astatobenzylguanidine ([²¹¹At]MABG), as much as a 3-log cell kill was observed in limiting dilution clonogenic assays. Exposure to considerably higher activity levels of [²¹¹At]astatide was required to achieve a similar degree of cell kill, suggesting that this cytotoxicity was not related to nonspecific effects of -particle irradiation. We conclude that the uptake capacity of medulloblastoma cell lines for [¹³¹I]MIBG uptakein vitro, while lower than that seen in SK-N-SH neuroblastoma cells, is sufficient to permit [²¹¹At]MABG to be used with significant therapeutic effectiveness.     

Contribution of registered and/or fused images to radiotherapy]

The quality of treatment that one can realize today in conformal radiotherapy, can be reached only if one has access to 3D imaging allowing a precise determination of the volume of the organs at risk and of the GTV. For this reason, one has access to anatomical imaging, CT or MRI, and functional and metabolic imaging, PET or SPECT imaging. CT gives the electronic density of the tissues, which is essential to ensure a very precise calculation of dose distribution. Its insufficiency in the visualization of the tumour and some anatomical structures makes necessary the registration of these images with MRI of which distortions are sufficiently weak to be usable in radiotherapy. The registration will be usable only if images of each modality are realised with the patient in treatment position, except for brain, where only CT, on which is based the registration, must be done in treatment position. The images registration is also called images fusion by some authors. Others consider fusion of images as a way to display registered images on a screen, specially for CT images and PET, and MRI and SPECT. Nevertheless, the fusion of images is a function offered by some softwares. It allows obtaining a single volume of voxels from those of the registered images (CT and MR images). This volume is not usable in radiotherapy because it keeps only partially the contributions of the CT scan images and the MRI. At least, if one wants to visualize the active parts of a tumour or to make the difference between fibrosis and tumour left or recurrence after radiotherapy or chemotherapy, it is necessary to use PET or SPECT. To define correctly the CTV using these images, one must realize the anatomical localization of the metabolic abnormalities, which they highlight with a registration based on CT or MRI. The difficulties to obtain the registration of these images led the manufacturer to propose mixed machines allowing realizing, at the same time, a CT imaging and a PET or a SPECT imaging with the patient in treatment position.     

Therapeutic implications of molecular imaging with PET in the combined modality treatment of lung cancer

Molecular imaging with PET, and certainly integrated PET-CT, combining functional and anatomical imaging, has many potential advantages over anatomical imaging alone in the combined modality treatment of lung cancer. The aim of the current article is to review the available evidence regarding PET with FDG and other tracers in the combined modality treatment of locally advanced lung cancer. The following topics are addressed: tumor volume definition, outcome prediction and the added value of PET after therapy, and finally its clinical implications and future perspectives.The additional value of FDG-PET in defining the primary tumor volume has been established, mainly in regions with atelectasis or post-treatment effects. Selective nodal irradiation (SNI) of FDG-PET positive nodal stations is the preferred treatment in NSCLC, being safe and leading to decreased normal tissue exposure, providing opportunities for dose escalation. First results in SCLC show similar results. FDG-uptake on the pre-treatment PET scan is of prognostic value. Data on the value of pre-treatment FDG-uptake to predict response to combined modality treatment are conflicting, but the limited data regarding early metabolic response during treatment do show predictive value. The FDG response after radical treatment is of prognostic significance. FDG-PET in the follow-up has potential benefit in NSCLC, while data in SCLC are lacking. Radiotherapy boosting of radioresistant areas identified with FDG-PET is subject of current research.Tracers other than ¹⁸FDG are promising for treatment response assessment and the visualization of intra-tumor heterogeneity, but more research is needed before they can be clinically implemented.     

Development of a real-time polymerase chain reaction assay for prediction of the uptake of meta-[(131)I]iodobenzylguanidine by neuroblastoma tumors.

PURPOSE: The suitability of neuroblastoma patients for therapy using radiolabeled meta-iodobenzylguanidine (MIBG) is determined by scintigraphy after the administration of a tracer dose of radioiodinated MIBG whose uptake is dependent upon the cellular expression of the noradrenaline transporter (NAT). As a possible alternative to gamma camera imaging, we developed a novel molecular assay of NAT expression. mRNA extracted from neuroblastoma biopsy samples, obtained retrospectively, was reverse transcribed, and NAT-specific cDNA was quantified by real-time PCR, referenced against the expression of the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase. EXPERMENTAL DESIGN: Tumor specimens from 54 neuroblastoma patients were analyzed using real-time PCR, and NAT expression was compared with the corresponding diagnostic scintigrams. RESULTS: Forty-eight of 54 (89%) of tumors showed MIBG uptake by scintigraphy. NAT expression was found to be significantly associated with MIBG uptake (P < 0.0001, Fisher's exact test). None of the samples from the six tumors that failed to concentrate MIBG expressed detectable levels of the NAT (specificity = 1.0). However, of the 48 MIBG uptake-positive tumors, only 43 (90%) expressed NAT (sensitivity = 0.9). The real-time PCR test has a positive predictive value of 1.0 but a negative predictive value of 0.55. CONCLUSIONS: The results indicate that whereas this method has substantial ability to predict the capacity of neuroblastoma tumors to accumulate MIBG, confirmation is required in prospective studies to determine more accurately the predictive strength of the test and its role in the management of patients with neuroblastoma.     

Increase of metaiodobenzylguanidine uptake and intracellular half-life during differentiation of human neuroblastoma cells

Iodine-labelled metaiodobenzylguanidine (MIBG) is a radio-pharmaceutical used for diagnostic imaging and targeted radiotherapy of neuroendocrine tumors. We previously reported that the ability of a neuroblastoma (NB) cell line, LAN-5, to accumulate MIBG was powerfully stimulated by interferon-γ (IFN-γ), a well-known NB differentiation-promoting agent. To extend the above findings, we have investigated 5 NB cell lines for their ability to accumulate ¹²⁵I-MIBG in basal conditions or after various combinations of differentiative stimuli. Our results show that association of IFN-γ and tumor necrosis factor-α boosts MIBG uptake in the early times of incubation in LAN-5 and GI-LI-N cells, while both 5K-N-SH and SK-N-BE(2)c cells are strongly stimulated by co-treatment with IFN-ggr; and all-trans retinoic acid. Moreover, although only LAN-5 and GI-LI-N cells are sensitive to IFN-γ alone, the combination of IFN-γ and IFN-α causes a synergistic increase in MIBG uptake in all the NB cell lines tested. From experiments on MIBG release we conclude that no intracellular storage within specialized structures took place during differentiation. The observed enhancement in MIBG accumulation results from an increased uptake of the drug only. This conclusion was confirmed by analyzing MIBG-transporter gene expression, which was increased in cells subjected to differentiative regimens. According to these findings, inducing differentiation of NB cells in vitro appears to improve their MIBG incorporation ability powerfully. © 1996 Wiley-Liss, Inc.     

The Impact of 123I-Meta-Iodobenzylguanidine Scintigraphy on Diagnostics and Follow-up of Neuroblastoma

The present retrospective study includes all children suspected for having neuroblastoma, admitted to Odense University Hospital in September 1984 through December 1993. Thirty-six children at the age range of 1 month to 14 years and 10 month were investigated with ¹²³I-metaiodobenzylguanidine (MIBG). Nineteen children had histologically verified neuroblastoma. Several MIBG scintigraphic examinations were made in all but one of these 19 children. Positive MIBG scintigraphy strengthened the diagnosis and indicated the volume and location of the tumour at diagnosis and during the treatment period. In a few patients only there was some disagreement between results obtained with MIBG scintigraphy and standard investigations as CT-scanning or ultrasonography. MIBG scintigraphy in all cases turned out to be the most sensitive modality.     

Imaging in head and neck cancer

Opinion statement The goals of imaging in head and neck cancer are to establish tumor extent and size, to assess nodal disease, to evaluate for perineural tumor spread, and to distinguish recurrent tumor from post-treatment changes. MRI is the preferred modality for assessment of nasopharyngeal, sinonasal, and parotid tumors, because of better contrast resolution, high frequency of perineural spread, and less prominent motion artifacts. MRI is the best modality to delineate the extent of intraorbital and intracranial extension of malignant tumors. Tumors of the oropharynx, larynx, and hypopharynx are frequently primarily imaged with CT, which is less affected by breathing and swallowing artifacts. MRI is also the initial study of choice for tumors confined to the oral tongue, and possibly also for other oral cavity locations because MRI is superior in detection of tumor spread into the bone marrow. There is no clear advantage of CT or MRI for evaluation of nodal disease. Positron emission tomography (PET) is very sensitive for metastatic lymph nodes that are at least 8 mm in size and is the technique of choice in dubious cases. Imaging-guided biopsies are performed whenever needed. For imaging of treated head and neck cancer, PET scans have been found to generally offer higher sensitivity than MRI or CT. Combined PET/CT may be the modality of choice because it almost completely eliminates the false-positive and false-negative PET findings. Patients with head and neck cancer who are referred to tertiary care centers commonly arrive with cross-sectional images obtained at other institutions. Reinterpretation of these studies by dedicated radiologists frequently leads to changes in findings, which alter treatment and affect prognosis.