Implications of Ambient Glucose Variation on the Target-to-Background Ratio of Hepatic Tumors By (18)FDG-PET Imaging.

OBJECTIVES: To investigate the effects of ambient glucose on quantitative analysis of hepatic tumors on 2-deoxy-2-((18)F)-fluoro-D-glucose ((18)FDG) positron emission tomography (PET) and to establish a method for glucose correction. PATIENTS AND METHODS: Eighty-six patients with hepatic lesions identified on (18)FDG PET/computed tomography (CT) were analyzed. The serum glucose level (Glc) was recorded prior to imaging, and the maximum standardized uptake value (SUV) in the hepatic tumors and the average SUV in normal liver were determined. The inverse relationship of SUV to glucose can be defined as d (SUV)/d (Glc) = g*SUV/(Glc), where g is the glucose sensitivity. Simulations using glucose level from 70 to 250 mg/dl were performed to evaluate the effects of Glc on the maximum SUV of malignant hepatic lesions and normal liver. RESULTS: By logarithmic transformation and linear regression, g for metastasis was significantly higher than that for normal liver (-0.636 ± 0.144 vs. -0.0536 ± 0.0583; P = 0.00092). Simulation studies showed that the SUV in malignant lesions will decrease rapidly when Glc level is >120 mg/dl, while background liver remains relatively constant up to 250 mg/dl. CONCLUSION: The tumor FDG uptake is much more sensitive to ambient glucose level variation than the background liver. Therefore, correction by the glucose sensitivity factor will result in more accurate SUV measurements and make semi-quantitative analysis of (18)FDG PET scans more reliable.

Use of SPECT/CT with 99mTc-MDP bone scintigraphy to diagnose sacral insufficiency fracture.

Bone SPECT/CT offers additional information on pelvic insufficiency fractures, especially when there is incomplete formation of the H-sign on planar bone scanning.

Improvement of hepatic lesion characterization by 18F-FDG PET/CT with the use of the lesion to background liver activity ratio.

OBJECTIVE: This study aimed to develop a reproducible method to improve (18)F-FDG PET/CT's diagnostic accuracy when characterizing hepatic lesions. METHODS: This was a retrospective study of 76 patients with various types of cancer who had 134 liver lesions described on diagnostic CT, MRI, or (18)F-FDG PET/CT. All 134 lesions were imaged by PET/CT. For comparison, all 134 lesions were also imaged either by MRI (58 lesions) or by diagnostic CT (107), with some imaged by both. The original reader's interpretation was used to determine the diagnostic validity of each modality. The (18)F-FDG PET/CT findings were then re-stratified using the ratio of the SUV(max) of the liver lesion to the SUV(avg) of liver background (SUV(TLR)). The standard of reference was histopathology and/or imaging follow-up. Eighty-nine out of the 134 lesions were positive for metastases. Two-tailed P values were calculated using a chi-square test. RESULTS: A SUV(TLR) greater than 2.0 strongly correlated with metastasis, while less than 2.0 strongly correlated with benign activity. Based on the original interpreter's visual analysis (PET(VA)), (18)F-FDG PET/CT had an accuracy of 74.6% with a high sensitivity (95.5%), but limited specificity (33.3%). Using the SUV(TLR) cutoff value of 2.0 to objectively re-stratify these cases, there was improvement in accuracy to 97.8%, sensitivity to 100%, and specificity to 93.3%. These values were statistically significant by chi-square analysis, with P = 0.0001 for both PET(VA) and SUV(TLR). The 58 MRI lesions and 107 diagnostic CT lesions that were reviewed had accuracies of 70.7% (P = 0.008) and 73.8% (P = 0.0001), respectively. CONCLUSION: Using a cutoff value of 2.0 for SUV(TLR) to objectively evaluate for potential hepatic metastases on (18)F-FDG PET results in a significant improvement in diagnostic accuracy over subjective visual analysis alone. In this limited study, use of SUV(TLR) more accurately characterized hepatic lesions than the original CT or MRI interpretations.

Positron emission tomography-computed tomography imaging characteristics of an inferior vena cava tumor thrombus with magnetic resonance imaging correlation.

Thrombus of the renal vein or inferior vena cava is a known complication of renal cell carcinoma (RCC). Accurate discrimination between bland and malignant thrombus can have significant implications toward clinical management. Distinguishing between these 2 entities is not usually possible with enhanced computerized tomography (CT) or magnetic resonance imaging. This case reports the role of combined positron emission tomography-CT imaging in the accurate detection of recurrent RCC after partial nephrectomy and surgically proven tumor thrombus in the renal vein and inferior vena cava.