Neurolymphomatosis with Spinal Nerve Root Involvement Demonstrated on 18F-FDG PET/CT.

A 56 years old woman with a diagnosis of diffuse large B-cell lymphoma had dyspnea, weakness in the left upper extremity and vocal cord paralysis after chemotherapy. She underwent cervical, thoracal and lumbosacral magnetic resonance imaging (MRI) however findings on MRI could not entirely explain the symptoms of the patient. Therefore, the patient underwent 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography and the scan revealed focal symmetrical 18F-FDG uptake on the cervical, thoracal and lumbal spinal nerve roots. Considering the symptoms of the patient and cerebrospinal fluid cytology findings, hypermetabolic spinal nerve roots were interpreted as lymphoma involvement.

FDG PET/CT and Conventional Imaging Methods in Cancer of Unknown Primary: an Approach to Overscanning.

PURPOSE: To compare the performance of fluorine-18 fluorodeoxyglucose positron emission tomography and computed tomography (FDG PET/CT) with conventional imaging methods (CIM), including computed tomography (CT), magnetic resonance imaging (MRI), and mammography (MMG) in cancer of unknown primary (CUP). METHODS: A total of 36 patients with CUP, who referred to our clinic for a FDG PET/CT scan, were enrolled in this study. Thirty of the patients were also examined through either diagnostic CT/MRI and/or MMG. The diagnostic performance of both methods for the primary cancer location was analyzed. The results of FDG PET/CT and CIM were compared based on the standard reference of the histopathology and/or clinical and laboratory follow-up. RESULTS: The primary cancer locations were detected in 24 patients (66.6%, 24/36) by FDG PET/CT, whereas CIM identified the locations in 16 patients (53.3%, 16/30). Sensitivity, specificity, PPV, NPV, and accuracy rates of the detection of the primary tumor localizations were as follows: 83, 70, 89, 58, and 79% for FDG PET/CT; 70, 62, 84, 42, and 68% for CIM, respectively. There was no statistical significance between modalities regarding any of the categories in 30 patients. CONCLUSION: FDG PET/CT detected the primary tumors of the patients with CUP more than CIM did. However, the difference between them was not found to be statistically significant. It may be considered that FDG PET/CT scan can be performed as a first-line tool in the initial diagnosis of the patients with CUP and to add radiodiagnostic imaging in selective cases. We conclude that if the first-line examination of a CUP patient has been already performed by a CIM and the result was negative or inconclusive, FDG PET/CT can be considered to avoid unnecessary imaging procedures.

Comparison of atherosclerotic inflammation and calcification in subjects with end stage renal disease (ESRD) on hemodialysis to normal controls utilizing 18F-FDG PET/CT.

OBJECTIVE: Subjects with end stage renal disease (ESRD) are exposed to increased morbidity and mortality due to cardiovascular events. The primary underlying mechanism has been suggested as accelerated atherosclerosis in these patients. Our aim was to compare the atherosclerotic inflammation and calcification in subjects with ESRD on hemodialysis to that in normal controls utilizing fluorine-18-2-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (18F-FDG PET/CT). SUBJECTS AND METHODS: Forthy two subjects who underwent 18F-FDG PET/CT imaging were retrospectively studied. Twenty one were subjects with ESRD on hemodialysis (67±11 years old; 14 male, 7 female) and 21 were age- and gender-matched controls. Average standardized uptake value maximum (SUVmax) and SUVmean for 4 segments of the aorta (ascending, arch, descending, abdominal) and for the common iliac arteries and common femoral arteries were measured. Standardized uptake value maximum and SUVmean for right atrial blood pool were also measured as the background. Average SUVmax, average SUVmean, average SUVmax/background ratio, and average SUVmean/background ratio were compared between subject groups for all segments. Presence or absence of macroscopic calcification on CT images for each arterial segment based on visual qualitative assessment was also noted and compared. For statistical analysis, two-sided t-test was used for continuous variables, and chi-square test was used for categorical variables. We considered a P value of <0.05 as statistically significant. RESULTS: Average SUVmax and SUVmean were statistically significantly greater in subjects with ESRD than in controls in all arterial segments. Average SUVmax/background ratios were statistically significantly greater in subjects with ESRD compared to normal controls in all arterial segments except for the left femoral artery. Average SUVmean/background ratios were statistically significantly greater in subjects with ESRD compared to normal controls in all arterial segments except for the right and left femoral arteries. Presence of calcification on CT was more frequently encountered in all arterial segments in subjects with ESRD, and was statistically significantly greater for the aortic arch, descending aorta, and right and left femoral arteries. CONCLUSION: SUV measurements representing the atherosclerotic inflammatory changes and macroscopic atherosclerotic calcifications appear to be accelerated in subjects with ESRD on hemodialysis compared to normal controls. Fluorine-18 FDG PET/CT is a valuable diagnostic tool for verifying and quantifying accelerated atherosclerosis secondary to ESRD.

Is 18F-FDG PET/CT a valuable diagnostic tool for verifying accelerated atherosclerosis secondary to diabetes mellitus on insulin in the aortic segments and large arteries?

OBJECTIVE: Fluorine-18 fluorodeoxylglucose positron emission tomography/computed tomography (18F-FDG PET/CT) has a well-established role for detection and quantification of atherosclerotic inflammatory disease using standardized uptake value (SUV) measurements. Our aim was to compare the inflammatory and macroscopic calcification processes of atherosclerosis in the aortic segments and large arteries of subjects with insulin dependent diametes mellitus (IDDM) compared to those of age-matched controls via 18F-FDG PET/CT. PATIENTS AND METHODS: A hundred and ten subjects who underwent 18F-FDG PET/CT imaging for oncological diseases were retrospectively studied. Fifty five were diabetics on insulin and 55 were age-matched controls. Average SUVmax and SUVmean for four segments of aorta and for common iliac arteries and femoral arteries were measured and compared between subject groups. Presence or absence of macroscopic calcification on CT images for each arterial segment was also noted and compared between these groups. RESULTS: Average SUVmax and SUVmean were statistically significantly greater in subjects with IDDM compared to controls in all arterial segments (P≤0.001). Presence of calcification on CT was more frequently encountered in 6 of the 8 segments in subjects with IDDM, and there was statistically significantly difference for the descending aorta and abdominal aorta. CONCLUSION: Our results show that inflammatory component of atherosclerosis was more severe in all aortic segments in subjects with IDDM compared to those of controls. Presence of macroscopic calcification also detected to be more frequently encountered in the descending thoracic and abdominal aorta in subjects with IDDM. Fluorine-18-FDG PET/CT is a valuable diagnostic tool for detecting and semi-quantifying accelerated atherosclerotic inflammatory and calcific changes secondary to diabetes mellitus treated with insulin in the aortic segments and large arteries.

Use of 111In-pentetreotide scan in a subject with treatment refractory atypical meningioma.

A 57-year-old man with a history of multiple recurrent atypical meningiomas (World Health Organization grade II) had several surgical resections including γ knife resection of the parafalcine meningioma, followed with a stereotactic radiosurgical ablation. Despite these treatments, an MRI scan performed 7 months later showed progression of the disease. The patient remained symptomatic with intermittent severe headaches associated with nausea, vomiting, and visual disturbance. He had a positive In-pentetreotide indicating the presence of somatostatin receptors. Therefore, he was placed on systemic Sandostatin (octreotide acetate) treatment, and at follow-up, he was clinically responsive to treatment.

Intermittent cystocele diagnosed on 18F-FDG PET/CT scan.

A 78-year-old woman was diagnosed with stage III diffuse large B-cell lymphoma, and treated with chemotherapy in 2004. Imaging follow-up was performed by serial 6-month diagnostic PET/CT scans. A PET/CT scan performed in June 2011 showed an unusual hourglass appearance of activity in the pelvis that prompted further investigation. Retrospective review of the prior diagnostic PET/CT scans revealed that the patient had a sliding bladder, located either above or below the pubococcygeal line at different imaging times, but during this scan, the bladder was "caught" moving up to its normal position.

Nuclear imaging of a pregnant patient: should we perform nuclear medicine procedures during pregnancy?

UNLABELLED: Although it is extremely rare, nuclear imaging of a pregnant woman presents a unique challenge to the nuclear medicine physician because of the high concern for radiation risk to the embryo or the fetus. This challenge has been exacerbated due to recent heightened public concern of medical procedures involving radiation. This awareness also has been emphasized to the referring physicians to the extent that the risks of most nuclear medicine scans are overstressed relative to the benefit. Radionuclide procedures are reluctantly ordered by clinicians in pregnant patients, because of the malpractice fear or because of uncertainty regarding fetal radiation dose. However, when used appropriately, the benefits of nuclear imaging procedures usually outweigh the minimal risks associated with small amount of radiation even in pregnant patients. CONFLICT OF INTEREST: None declared.

Rare case of Primary Pulmonary Extranodal Non-Hodgkin's Lymphoma in a Patient with Sjogren's Syndrome: Role of FDG-PET/CT in the Initial Staging and Evaluating Response to Treatment.

UNLABELLED: A 64-year old woman with a long standing Sjogren's syndrome was undergoing evaluation for renal transplant surgery when two pulmonary opacities were detected on chest CT. Subsequent biopsy revealed extranodal marginal B-cell non-Hodgkin's lymphoma (NHL). An FDG-PET/CT scan was then performed which demonstrated isolated FDG avid pulmonary involvement. After therapy, FDG-PET/CT scans showed good response to treatment with near complete resolution of FDG avidity. This rare case illustrates the rare pulmonary manifestation of extranodal lymphoma in a patient with Sjogren's syndrome and emphasizes the value of FDG PET/CT in the initial staging and evaluation of response to treatment, which has not previously been published. CONFLICT OF INTEREST: None declared.

Improved Benefit of SPECT/CT Compared to SPECT Alone for the Accurate Localization of Endocrine and Neuroendocrine Tumors.

OBJECTIVE: To assess the clinical utility of SPECT/ CT in subjects with endocrine and neuroendocrine tumors compared to SPECT alone. MATERIAL AND METHODS: 48 subjects (31 women;17 men; mean age 54±11) with clinical suspicion or diagnosis of endocrine and neuroendocrine tumor had 50 SPECT/CT scans (32 Tc-99m MIBI, 5 post treatment I-131, 8 In-111 Pentetreotide, and 5 I-123 MIBG). SPECT alone findings were compared to SPECT/CT and to pathology or radiological follow up. RESULTS: From the 32 Tc-99m MIBI scans, SPECT accurately localized the lesion in 22 positive subjects while SPECT/CT did in 31 subjects. Parathyroid lesions not seen on SPECT alone were smaller than 10 mm. In five post treatment I-131 scans, SPECT alone neither characterized, nor localized any lesions accurately. SPECT/CT revealed 3 benign etiologies, a metastatic lymph node, and one equivocal lesion. In 8 In-111 Pentetreotide scans, SPECT alone could not localize primary or metastatic lesions in 6 subjects all of which were localized with SPECT/CT. In five I-123 MIBG scans, SPECT alone could not detect a 1.1 cm adrenal lesion or correctly characterize normal physiologic adrenal uptake in consecutive scans of the same patient with prior history of adrenelectomy, all of which were correctly localized and characterized with SPECT/CT. CONCLUSION: SPECT/CT is superior to SPECT alone in the assessment of endocrine and neuroendocrine tumors. It is better in lesion localization and lesion characterization leading to a decrease in the number of equivocal findings. SPECT/CT should be included in the clinical work up of all patients with diagnosis or suspicion of endocrine and neuroendocrine tumors. CONFLICT OF INTEREST: None declared.

Tc-99m red blood cell bleeding scan in a pregnant woman presenting with hematemesis: a brief review of indications and guidelines for radionuclide scans during pregnancy.

A 6-month pregnant 35-year-old woman with hematemesis and dark blood in her stool was evaluated for location of an active gastrointestinal bleeding site. The findings from 2 esophagogastroduodenoscopies and a colonoscopy were negative. The patient was referred for a Tc-99m red blood cell scintigraphy, for location of an active bleeding site. As the patient was 6 months pregnant, the necessity of the case was discussed with the patient's referring physician and after determining that this study was necessary, the risk of radiation exposure to the fetus was discussed with the radiation safety officer and the patient. The procedure was performed after the patient signed informed consent regarding the considerations of radiation safety to the fetus. The Tc-99m red blood cell bleeding scan clearly shows activity in the fetus in addition to a large arteriovenous malformation in the patient. The visualized fetus prompted this report to discuss radiation risks concerns and a brief review of indications and guidelines for performing nuclear medicine procedures in pregnant patients.

Increased 18F-FDG uptake within the reticuloendothelial system in patients with active lung cancer on PET imaging may indicate activation of the systemic immune response.

The reticuloendothelial system (RES) cells are in the defense against certain pathogens, and in the removal of dying cells, cell debris, microorganisms, and malignant cells. Liver, spleen, and bone marrow represent the major organs with high RES activity. We hypothesized that in subjects with active lung cancer, the metabolic activity of these organs would be greater than that of the subjects with no active tumor. We have studied two groups of subjects who had undergone (18)F-FDG-PET imaging for clinical purposes. The first group consisted of 39 subjects (20 women, 19 men, mean age 64.8+/-10.2 years) with benign lung nodules as demonstrated by (18)F-FDG-PET imaging. The second group consisted of 30 subjects (18 women, 12 men; mean age 65.1+/-11 years) who were known to have active lung cancer with or without distant metastases as seen on (18)F-FDG-PET imaging. The subjects in the second group did not have any evidence of liver, spleen, bone marrow, or heart involvement on (18)F-FDG-PET images. We measured the mean SUV of the liver, spleen, bone marrow, heart, and of the contralateral unaffected lung, and compared the average SUV for these organs between the two groups. We found that the mean SUV of the liver, bone marrow, and spleen were significantly greater in subjects with evidence of active primary or metastatic lung cancer compared with those of subjects who had benign lung nodules and no evidence of active malignant disease. There was a statistically significant difference between mean SUV for organs noted above between the two groups (P<0.05). In contrast, mean SUV for the heart and contralateral normal lung did not show any significant difference between the two groups. In conclusion, the mean SUV for the major organs of RES, liver, spleen, and bone marrow were higher in subjects with active lung cancer with or without metastases than in those without active malignancy. We believe these differences in SUV may indicate a differential activation of the systemic immune response, related to the presence or absence of active lung cancer, which can be detected and quantified non-invasively through (18)F-FDG-PET imaging.

Tumor metabolism measured by partial volume corrected standardized uptake value varies considerably in primary and metastatic sites in patients with lung cancer. A new observation.

Fluorine-18 fluorodeoxyglycose -position emission tomography ((18)F-FDG-PET) as an efficient staging tool for lung carcinoma; allows description and characterization of the primary tumor and of local and distant metastases in a single examination. One of the important limiting factors in quantification of metabolic parameters with PET is the partial volume effect. Our aim for this study was to delineate tumor (size) both in the primary and metastatic lesions in patients with lung cancer by using partial volume correction techniques. Thirty two patients with proven lung cancer who had (18)F-FDG-PET and computerized tomography (CT) within the last 80 days were involved in this study. They were 18 women and 14 men, with age range 43-83 years. Maximum standardized uptake values (SUVmax) in primary and metastatic lesions for all patients were measured. The lesions were categorized into 4 different Groups according to their site. Partial volume corrections were applied using the CT sizes of lesions to obtain corrected SUVmax values. Average corrected SUVmax in each lesion site was calculated and compared between the 4 Groups. A total of 81 primary and metastatic lesions were included in this analysis. They were 28 mediastinal-hilar lymph node lesions, 26 lung lesions, 11 solid organ lesions, and 16 bone marrow lesions. The average uncorrected SUVmax for the primary lung lesions, mediastinal-hilar lymph node lesions, solid organ lesions, and the bone marrow lesions before application of partial volume correction formula were 7.2+/-3.2; 7.0+/-2.7; 6.3+/-3.4 and 7.0+/-3.4, respectively. The average corrected SUVmax for the lesions in the above mentioned regions were 11+/-6, 10+/-4, 13+/-7, and 18+/-13, respectively. A statistically significant difference was observed in the average SUVmax values between lung lesions and nodal lesions compared to the bone marrow lesions. In conclusion, our findings indicate that metabolic activities of lung cancer lesions vary depending on the sites of metastatic disease.

A pilot study of changes in (18)F-FDG uptake, calcification and global metabolic activity of the aorta with aging.

Our aim was to quantify changes in the inflammatory and calcific components of atherosclerosis in the aortic wall using fluoro-18-2-fluoro-2-deoxy-D-glucose positron emission tomography (18)F-FDGPET and contrast enhanced computerized tomography (CECT) with increasing age. Twelve subjects, 8 men and 4 women aged from 21-80 years who had both (18)F-FDG-PET and CECT of the chest and abdomen were included in this study. Subjects were grouped into three according to age. (18)F-FDG uptake in four segments of the aorta was measured. Using CECT images, aortic segmental wall volumes were measured. Wall calcification volume in each aortic segment was also measured via adaptation of a coronary artery calcium-scoring program to the aorta. Calcification volumes were then subtracted from aortic wall volumes. Each net segmental aortic wall volume was then multiplied by the accompanying mean SUV of the segment to calculate global metabolic activity (GMA) for each aortic segment. Our results showed that in each aortic wall segment, mean SUV, wall volumes, wall calcification volumes, and GMA statistically significantly increased with age. In conclusion, (18)F-FDG uptake, wall volume, wall calcification volume, and GMA in the aorta increase with aging. The (18)F-FDG uptake represents the early inflammatory component of the atherosclerotic process, whereas calcification generally represents a later and irreversible stage of the disease. Measurement and combination of PET and CECT parameters to calculate GMA may allow for optimal morphologic and functional noninvasive quantitative assessment of global aortic atherosclerotic disease.

A recovery coefficient method for partial volume correction of PET images.

OBJECTIVES: Correction of the "partial volume effect" has been an area of great interest in the recent times in quantitative PET imaging and has been mainly studied with count recovery models based upon phantoms that incorporate hot spheres in a cold background. The goal of this research study was to establish a similar model that is closer to a biological imaging environment, namely hot spheres/lesions in a warm background and to apply this model in a small cohort of patients. METHODS: A NEMA phantom with six spheres (diameters 1-3.7 cm) was filled with (18)FDG to give sphere:background activity ratios of 8:1, 6:1, and 4:1 for three different acquisitions on a Philips Allegro scanner. The hot sphere SUVmax and the background average SUV were measured for calculation of recovery coefficients (RCs). Using the RCs, the lesion diameters, and the lesion:background ratio, the SUVmax of 64 lesions from 17 patients with biopsy proven lung cancer were corrected. RESULTS: The RCs versus sphere diameters produced characteristic logarithmic curves for each phantom (RCs ranged from 80% to 11%). From a cohort of 17 patients with biopsy proven lung cancer, 64 lesions combined had a mean SUVmax of 7.0 and size of 2.5 cm. After partial volume correction of the SUVmax of each lesion, the average SUVmax increased to 15.5. CONCLUSIONS: Hot spheres in a warm background more closely resemble the actual imaging situation in a living subject when compared to hot spheres in a cold background. This method could facilitate generation of equipment specific recovery coefficients for partial volume correction. The clinical implications for the increased accuracy in SUV determination are certainly of potential value in oncologic imaging.

Usefulness of non attenuation corrected 18F-FDG-PET images for optimal assessment of disease activity in patients with lymphoma.

This study aimed at determining whether non attenuation corrected (NAC) positron emission tomography (PET) images, in addition to the attenuation corrected (AC) PET images, should be included in the interpretation of fluoro-18 fluorodeoxyglucose ((18)F-FDG-PET) images in patients with lymphoma. The study included 58 patients, 35 males 23 females, mean age 55+/-16 years. There were 64 superficial and 170 deep lymph node (LN) lesions. Lesion detection, uptake intensity using a three-point scale (1-mild, 2-moderate, 3- intense) and overall clarity of each lesion were compared on both PET images. Our results showed that the detection rate for superficial LN was 100% for NAC-PET and 98.4% for AC-PET images. The degree of (18)F-FDG uptake (intense, moderate and mild uptake) was 56.3%, 31.3% and 12.5% for NAC-PET images and 23.4%, 34.4% and 40.6% for AC-PET images, respectively. The overall image clarity was significantly in favor of NAC compared to AC-PET images (89% vs 20%, P<0.01). For deep LN, lesions, detection rate was for NAC and AC-PET images 95.3% and 99.4%, respectively. (18)F-FDG uptake intensity (intense, moderate and mild uptake) was 42.4%, 27.1% and 25.9% for NAC and 52.4%, 43% and 4.1% for AC-PET images, respectively. The overall image clarity for AC-PET images was superior to NAC-PET images (81.8% vs 53% P=0.01). In conclusion, NAC-PET images appeared to be superior to AC-PET images in detecting superficial LN lesions. AC-PET images are superior to NAC-PET images with regard to the deep-seated LN lesions. Therefore, AC and NAC-PET images are complimentary to each other and require to be reviewed together in the evaluation of patients with lymphoma.

Impact of dual-time-point (18)F-FDG PET imaging and partial volume correction in the assessment of solitary pulmonary nodules.

PURPOSE: Our aim was to assess the diagnostic potential of (18)F-FDG PET using partial volume correction and dual-time-point imaging in the assessment of solitary pulmonary nodules. METHODS: We included 265 patients in this retrospective study (171 men; 94 women; age range, 41-92 years). All had pulmonary nodules on CT, and diagnosis was confirmed by biopsy or follow-up CT. All underwent whole body FDG PET, 60 min after FDG injection. Of the 265 patients, 255 underwent second FDG PET for chest 100 min after injection. Maximum SUVs for nodules were calculated from both scans. Partial volume correction for first time SUVs was applied, using coefficient factor. Malignancy was defined using the following criteria: (1) Visual assessment; (2) First time SUV > or = 2.5; (3) Partial volume corrected first time SUV > or = 2.5; (4) second time SUV > or = 2.5; (5) Increase in SUV over time; (6) Increase or no change in SUV; (7) First time SUV > or = 2.5 and/or increase or no change in SUV. RESULTS: Biopsy and follow-up revealed 72 malignant lung nodules and 193 benign nodules. Sensitivity, specificity and accuracy for the five criteria were as follows: (1) 97, 58 and 68%; (2) 65, 92 and 85%; (3) 84, 91 and 89%; (4) 90, 80 and 83%; (5) 84, 95 and 92%; (6) 92, 92, and 92%; (7) 95, 90 and 91%, respectively. CONCLUSION: Dual-time-point (18)F-FDG PET has potential impact on improving the diagnostic accuracy for malignant lung nodules. Dual-time-point (18)F-FDG PET imaging should be included in the clinical work-up of patients with pulmonary nodule.

FDG-PET is useful in staging and follow-up of primary uterine cervical lymphoma.

A 35-year old woman presented with vaginal bleeding. She had a normal gynecologic examination and Papanicolaou test. A CT scan of the pelvis showed a cervical mass, which on biopsy proved to be B-cell lymphoma. PET before preoperative staging demonstrated a large area of increased FDG uptake in the pelvis, corresponding to the mass seen on the CT scan. There were no other abnormal F-18 FDG avid sites. The patient received chemotherapy followed by total abdominal hysterectomy. Histopathology was consistent with large B-cell lymphoma of the uterine cervix. Posttherapy CT scan and PET scan showed no evidence of active and or residual disease.

Novel quantitative techniques for assessing regional and global function and structure based on modern imaging modalities: implications for normal variation, aging and diseased states.

In this review, we describe the current approaches used for quantitative assessment of regional and global function with positron emission tomography (PET) imaging (combined with structural imaging modalities) with emphasis on both research and clinical applications of this powerful approach. We particularly refer to the impact of such measurements in assessing physiological processes such as aging and measuring response to treatment in serious disorders such as cancer. Although a multitude of methods has been described in literature, the optimal approaches that are both accurate and practical in clinical settings need to be defined and refined. Standardized uptake value (SUV) continues to be the most widely used index in the current practice. Calculating SUV at a single time point and assigning standard regions of interest are inadequate and suboptimal for the purposes adopted by the medical community. The concepts of partial volume correction for measured values in small lesions, dual-time point and delayed PET imaging, and global metabolic activity for assessment of various stages of disease may overcome deficiencies that are associated with the current quantitative (ie, SUV) techniques. Serious consideration of these concepts will enhance the role and reliability of these quantitative techniques, and therefore compliment the World Health Organization or the Response Evaluation Criteria in Solid Tumors (RECIST) criteria for managing patients with cancer and other disorders, including physiological states such as aging and serious diseases such as atherosclerosis and neurological diseases. We also introduce the concepts that allow for segmentation of various structural components of organs like the brain for accurate measurement of functional parameters. We also describe complicated kinetic modeling and methodologies that have been used frequently for assessing metabolic and pharmacological parameters in the brain and other organs. Simplified quantitative techniques based on these concepts are described, but should be validated against the kinetic models to test their role as practical tools.

Fluorodeoxyglucose-PET in the management of malignant melanoma.

FDG-PET is of limited use in patients with early-stage disease without nodal or distant metastases (stage I-II), because sentinel node biopsy is much more sensitive in detecting microscopic lymph node metastases. Because of the high tumor-to-background ratio, FDG-PET can highlight metastases at unusual sites that are easily missed with conventional imaging modalities. PET has been shown to have a strong role in detecting metastatic disease. FDG-PET is more sensitive than CT for detecting metastatic lesions in skin, lymph nodes, and abdomen, but CT is equivalent to or more sensitive than FDG-PET for detecting small pulmonary lesions. FDG-PET identifies the location and number of metastatic lesions in stage III and IV disease and therefore is important for surgical planning. Most of the false-negative FDG-PET results are caused by micrometastases and lesion smaller than 10 mm. Postsurgical inflammation, other inflammatory lesions, and some benign tumors cause some false-positive FDG-PET results.