Iatrogenic artifacts on whole-body F-18 FDG PET imaging

PURPOSE: Whole-body F-18 FDG PET images frequently show artifacts related to medical and surgical interventions. We present some of the common artifact patterns in this atlas article. MATERIALS AND METHODS: We studied whole-body F-18 FDG PET images of 30 adult patients (17 males and 13 females). Of these, 9 patients had lymphoma, 7 had colon cancer, 6 had lung cancer, 3 had lung nodules, 2 each had breast and bladder cancer, and 1 patient had brain cancer. All patients had a history of some surgical or medical intervention for malignant or some other associated disease. RESULTS: PET images of 8 patients showed artifacts related to implanted prostheses and ports and 9 patients showed artifacts related to percutaneous insertion or opening of catheters, tubes, and stomas. Six patients had artifacts from previous surgery, 3 from previous radiation therapy, 3 from previous chemotherapy, and 1 from changes in glucose metabolism. CONCLUSIONS: Medical and surgical interventions can give rise to artifacts on whole-body F-18 FDG PET images. The possibilities and patterns of these artifacts should be kept in mind while reporting these studies.     

Pancreatic pseudocyst observed on F-18 FDG PET imaging

A 72-year-old man with right lower lobe squamous cell carcinoma of the lung-status, post resection-and prostate carcinoma was referred for restaging with whole-body PET using F-18 FDG. PET images, in addition to the presence of moderate hypermetabolic activity seen in the left lower paratracheal and bilateral hilar regions, revealed a large hypometabolic space-occupying lesion in the abdomen. The appearance of this lesion was highly suggestive of a pancreatic pseudocyst. Further review of a CT scan performed 3 years ago confirmed the presence of a pancreatic pseudocyst. However, this information was not available to the nuclear medicine physician at the time of the PET examination.     

Catheter-related focal FDG activity on whole body PET imaging

INTRODUCTION: Whole body FDG positron emission tomography (PET) scan is increasingly being used in the management of a variety of cancers and infections. Cancer patients and other very sick patients have central venous catheters, which could be associated with common complications like thrombosis and infections. We describe catheter-related focal FDG uptake on whole body FDG PET scans in 4 patients. MATERIALS AND METHODS: Four patients underwent whole body FDG-PET scanning 60 minutes after intravenous injection of F18-FDG (2 for localization of site of infection, 1 for primary cancer site localization, and 1 for restaging of colon cancer). The whole body PET images were compared and correlated with the patients' history, radiology and laboratory tests. RESULTS: Focal and intense FDG activity is seen in all 4 patients at the distal end of the intravenous catheter. The average SUV of this activity was 6.3 (n = 3). Catheter-related thrombosis was identified as the cause of FDG activity in 3 patients, whereas catheter-related infection was considered in one patient. CONCLUSION: Focal and intense FDG activity, in relation to the distal end of a central venous catheter, has a benign etiology, usually seen with catheter-related venous thrombosis and can be seen with catheter related infection.     

Risk assessment in liposarcoma patients based on FDG PET imaging

Purpose Tumor grade and subtype are considered standard parameters for risk assessment in patients with liposarcoma. The aim of this study was to assess the clinical value of [¹⁸F]fluorodeoxyglucose (FDG) PET-derived maximum standardized uptake value (SUV_max) for prediction of outcome in liposarcoma patients.Methods ¹⁸F-FDG PET was performed in 54 patients with liposarcoma prior to therapy. SUV_max was calculated for each tumor and results were correlated with tumor grade, subtype, and relapse-free survival.Results SUV_max ranged from 0.4 to 15.9 (mean 3.6) and was significantly lower in grade I than in grade II and grade III tumors. SUV_max was 2.3±1.7, 3.5±1.5, 4.8±2.5, and 5.6±5.8 in well-differentiated, myxoid/round cell, dedifferentiated, and pleomorphic subtypes, respectively. Borderline differences (p=0.059) were found between tumor SUV_max in patients with and without relapse. Using a SUV of 3.6 as cut-off, the accuracy in predicting a relapse was 75%. Tumor grade yielded a lower accuracy for predicting relapse (50%), as did tumor subtype (35%). In Kaplan-Meier survival analysis, patients with a SUV_max >3.6 had a significantly shorter disease-free survival of 21 months compared with 44 months in patients with a SUV_max ≤3.6. Tumor grading and tumor subtype did not yield significant differences.Conclusion Pretherapy tumor SUV obtained by FDG PET imaging was a more useful parameter for risk assessment in liposarcoma than tumor grade or subtype. A SUV_max of more than 3.6 resulted in a significantly reduced disease-free survival and identified patients at high risk for developing early local recurrences or metastatic disease.     

Persistent non-specific FDG uptake on PET imaging following hip arthroplasty

Hip arthroplasty is a common surgical procedure, but the diagnosis of infection associated with hip arthroplasty remains challenging. Fluorine-18 fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) has been shown to be a promising imaging modality in settings where infection is suspected. However, inflammatory reaction to surgery can result in increased FDG uptake at various anatomic locations, which may erroneously be interpreted as sites of infection. The purpose of this study was to assess the patterns and time course of FDG accumulation following total hip replacement over an extended period of time. Firstly, in a prospective study nine patients with total hip replacement were investigated to determine the patterns of FDG uptake over time. Three FDG-PET scans were performed in each patient at about 3, 6 and 12 months post arthroplasty. Secondly, in a retrospective analysis, the medical and surgical history and FDG-PET imaging results of 710 patients who had undergone whole-body scans for the evaluation of possible malignant disorders were reviewed. The history of arthroplasty and FDG-PET findings in the hip region were reviewed for this study. Patients with symptomatic arthroplasties or related complaints during FDG-PET scanning were excluded from the analysis. During the entire study period, all nine patients enrolled in the prospective study were demonstrated to have increased FDG uptake around the femoral head or neck portion of the prosthesis that extended to the soft tissues surrounding the femur. Among the patients reviewed in the retrospective study, 18 patients with a history of 21 hip arthroplasties who were asymptomatic at the time of FDG-PET scan met the criteria for inclusion. The time interval between the hip arthroplasty and the FDG-PET study ranged from 3 months to 288 months (mean+/-SD: 80.4+/-86.2 months). In 81% (17 of 21) of these prostheses, increased FDG uptake could be noted around the femoral head or neck portion of the prosthesis. The average time interval between arthroplasty and FDG-PET scan in these patients was 71.3 months. In only four prostheses (19%, 4 of 21) was no abnormally increased FDG uptake seen around the prostheses or adjacent sites. The average time interval in these patients was 114.8 months. It is concluded that following hip arthroplasty, non-specifically increased FDG uptake around the head or neck of the prosthesis persists for many years, even in patients without any complications. Therefore, to minimize the number of false-positive results for infection with PET studies obtained to evaluate a painful hip prosthesis, caution should be exercised when interpreting FDG uptake around the head or neck portion of the prosthesis.     

FDG PET imaging of metastatic gastrointestinal stromal tumor

A 75-year-old woman presented with an 8-month history of progressive abdominal distension and associated weight loss. Computed tomography (CT) showed a very large, partially enhancing, cystic/solid mass within the abdomen that extended from below the left diaphragm to the pelvis. A large (10 cm), partially enhancing lesion was also seen in segments 6 and 7 of the right lobe of the liver, consistent with metastatic disease. The patient underwent laparotomy and resection of a 5.7-kg abdominal tumor measuring 30 x 27 x 20 cm. Histology confirmed a gastrointestinal stromal tumor (GIST) of stomach origin. A whole-body F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) scan performed 2 months postoperatively demonstrated multiple glucose-avid lesions in the liver as well as residual disease within the abdomen and pelvis. The patient was referred to medical oncology. The authors give a brief overview of this rare mesenchymal tumor of the gastrointestinal tract and the potential role of PET.     

Optimization of urinary FDG excretion during PET imaging.

Accumulation of fluorodeoxyglucose (FDG) activity in the urine interferes with the visualization of pelvic and, sometimes, abdominal abnormalities. Although this is a major problem, there are few data on the physiological variables affecting FDG urinary excretion that are critical to minimizing urinary FDG interference during PET imaging. METHODS: The excretion of FDG in urine was determined during 90 min in four groups of rats (n = 24) under the following conditions: normal, hydrated, hydrochlorothiazide treated and phlorizin treated. FDG clearance rates were measured in both normal and phlorizin-treated animals and compared with the glomeruler filtration rate measured with 99mTc-diethylenetriamine pentaacetic acid. We measured FDG excretion in 10 patients who had no known renal disease and were undergoing PET scanning (divided into two groups: hydrated and dehydrated) to relate the animal data to humans. RESULTS: The hydrated and phlorizin-treated animals had the highest excretion of FDG (39.68+/-5.00 % injected dose (%ID) and 45.64+/-9.77 %ID, respectively). Animals given the hydrochlorothiazide had the highest urinary volume, but the percentage excreted was comparable with the normal rats. Measurement of the clearance of FDG in animals before and after the administration of phlorizin determined the amount of FDG reabsorbed in the proximal tubules to be 56%+/-9.15%. The hydrated patients had a higher excretion of FDG than dehydrated patients (16.98+/-1.99 %ID versus 14.27+/-1.00 %ID, P < 0.021), and the volume of urine voided was significantly higher (P < 0.020). CONCLUSION: Hydrochlorothiazide increases urine volume without enhancing FDG excretion. The hydration of patients before PET scanning may lead to more FDG reaching the bladder. Reduction of bladder activity by more frequent voiding facilitated by increased urine volume in hydrated patients may be offset by increased delivery of FDG to the bladder. A preferable means of increasing urinary volume without increasing delivery of FDG to the bladder may be the use of a diuretic.     

F-18 FDG PET imaging in gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST) is the most frequent mesenchymal malignancy of the gastrointestinal tract. Liver and peritoneum are the most frequent metastatic sites. Surgery is the mainstay of treatment in patients with localized disease. Imatinib mesylate (Gleevec; Novartis Pharmaceuticals, East Hanover, NJ), an inhibitor of tyrosine kinase activity of KIT receptor, has been shown to be an effective treatment in metastatic or unresectable disease. Follow-up of patients treated with Gleevec is controversial. The authors present a case of GIST that showed near-total response with Gleevec on fluorodeoxyglucose positron emission tomography. They suggest positron emission tomography as a useful imaging modality for the monitoring of therapy response in GIST tumors treated with Gleevec.