Effect of iodine concentration of contrast media on contrast enhancement in multislice CT of the pancreas.

The purpose of this study was to determine the influence of two different iodine concentrations of the non-ionic contrast agent, Iomeprol, on contrast enhancement in multislice CT (MSCT) of the pancreas. To achieve this MSCT of the pancreas was performed in 50 patients (mean age 57+/-14 years) with suspected or known pancreatic tumours. The patients were randomly assigned to group A (n=25 patients) or group B (n=25 patients). There were no statistically significant differences in age, height or weight between the patients of the two groups. The contrast agent, Iomeprol, was injected with iodine concentrations of 300 mg ml(-1) in group A (130 ml, injection rate 5 ml s(-1)) and 400 mg ml(-1) in group B (98 ml, injection rate 5 ml s(-1)). Arterial and portal venous phase contrast enhancement (HU) of the vessels, organs, and pancreatic masses were measured and a qualitative image assessment was performed by two independent readers. In the arterial phase, Iomeprol 400 led to a significantly greater enhancement in the aorta, superior mesenteric artery, coeliac trunk, pancreas, pancreatic carcinomas, kidneys, spleen and wall of the small intestine than Iomeprol 300. Portal venous phase enhancement was significantly greater in the pancreas, pancreatic carcinomas, wall of the small intestine and portal vein with Iomeprol 400. The two independent readers considered Iomeprol 400 superior over Iomeprol 300 concerning technical quality, contribution of the contrast agent to the diagnostic value, and evaluability of vessels in the arterial phase. No differences were found for tumour delineation and evaluability of infiltration of organs adjacent to the pancreas between the two iodine concentrations. In conclusion the higher iodine concentration leads to a higher arterial phase contrast enhancement of large and small arteries in MSCT of the pancreas and therefore improves the evaluability of vessels in the arterial phase.

Preoperative diagnosis of ovarian tumors with MR imaging: comparison with transvaginal sonography, positron emission tomography, and histologic findings.

OBJECTIVE: Our study evaluated the diagnostic performance of MR imaging compared with that of transvaginal sonography and positron emission tomography (PET) in patients with clinically asymptomatic adnexal findings. An additional goal was to determine whether the combination of the three methods enhanced their diagnostic accuracy. SUBJECTS AND METHODS: Included in the study were 103 women with suspicious adnexal findings on sonography. Patients underwent transvaginal sonography, MR imaging, and PET within 3 weeks of the initial sonography. For MR imaging, axial and sagittal T1-weighted gradient-echo sequences (unenhanced and enhanced) and T2-weighted turbo-spin-echo sequences were acquired. Transvaginal sonography was performed with a 7.5-MHz transducer head. For PET, a modern full-ring scanner was used. The results of diagnostic imaging techniques were first evaluated separately, and reviewers were blinded to the results of other methods. Finally, a second session resulted in a consensus diagnosis based on the findings of all three methods. Results of histology were considered the gold standard. RESULTS: Histology revealed 12 malignant and 91 benign ovarian tumors. The following data were calculated for MR imaging, transvaginal sonography, PET, and consensus diagnosis: sensitivities, 83%, 92%, 58%, 92%; specificities, 84%, 59%, 78%, 84%; diagnostic accuracies, 83%, 63%, 76%, 85%, respectively. MR imaging, particularly with contrast-enhanced fat-saturated T1-weighted sequences, was found to correctly reveal dermoid and endometrial cysts. All three methods had false-negative findings with borderline tumors. CONCLUSION: Transvaginal sonography is the diagnostic method of choice as a screening technique for ovarian processes. Suspicious findings on transvaginal sonography should be confirmed on MR imaging. If MR imaging confirms a dermoid or endometrial cyst, further diagnostic procedures may be unnecessary. In all other cases, a surgical evaluation must be considered.

Classification of asymptomatic adnexal masses by ultrasound, magnetic resonance imaging, and positron emission tomography.

OBJECTIVE: The purpose of this study was to determine the diagnostic accuracy of sonography versus magnetic resonance imaging (MRI) and positron emission tomography (PET) in the characterization of adnexal masses. METHODS: One hundred and one patients with asymptomatic adnexal masses, which were scheduled for laparoscopy, underwent preoperative transvaginal ultrasound, MRI, and 2-[(18)F]fluoro-2-deoxy-d-glucose PET. Two different sonomorphological scoring systems were used to distinguish malignant from benign lesions. In addition, transvaginal Doppler flow velocimetry was performed and the resistance index (RI) of ovarian blood vessels was calculated. RI values below 0.45 were considered to indicate malignancy. MRI was evaluated on the basis of signal intensity and morphologic features such as wall thickness, septations, fluid or solid components, and vascularity. PET imaging was used to determine 2-[(18)F]fluoro-2-deoxy-D-glucose uptake. Malignancy was suspected if radiotracer uptake equaled or exceeded that of the liver. Based on histologic findings, sensitivity, specificity, positive and negative predictive values, and accuracy were first calculated independently for each imaging technique. Finally, a second session resulted in a consensus diagnosis being made based on the findings of all three modalities. RESULTS: Sonographic evaluation of adnexal masses resulted in correct classification of 11 of 12 ovarian malignancies (sensitivity 92%) but with a specificity of only 60%. With MRI and PET, specificities improved to 84 and 80% respectively, but sensitivities decreased. When all imaging modalities were combined, sensitivity and specificity were 92 and 85%, respectively, and accuracy was 86%. CONCLUSION: Combination of ultrasound with MRI and PET may improve accuracy in differentiation of benign from malignant ovarian lesions. However, negative MRI or PET results do not rule out early-stage ovarian cancer or borderline malignancies.

[Preoperative assessment of asymptomatic adnexal tumors by positron emission tomography and F 18 fluorodeoxyglucose]. / Präoperative Dignitätsbeurteilung asymptomatischer Adnextumoren mittels Positronen-Emissions-Tomographie und F-18-Fluordeoxyglukose.

AIM: To evaluate use of F-18-FDG-PET in assessment of dignity of asymptomatic adnexal masses. METHODS: 85 asymptomatic patients with suspicious, asymptomatic adnexal masses were evaluated. Static FDG-PET (Exact HR+ or ECAT 931) imaging of the abdomen was performed following application of 222-555 MBq F-18-FDG. Iterative reconstruction was applied. PET data were analysed visually, at first without and second together with MRT images. Final diagnosis was made by histopathology. RESULTS: FDG-PET allowed correct identification of 4 of 8 malignant adnexal tumors. False negative results were obtained in 2 adenocarcinomas stage pT1a and 2 borderline-tumors. In 60 out of 77 benign adnexal masses malignancy could be excluded. False positive FDG-uptake, partly because of misinterpretation of gastrointestinal activity, was found in 3 inflammatory processes, 1 teratoma, 1 benign schwannoma, 1 dermoid cyst, 1 benign thecoma, 1 serous cyst, 1 serous cystadenoma, 2 mucinous cystadenomas, 2 corpus luteum cysts, 3 endometriosic cysts and 1 sactosalpinx. The overall sensitivity and specificity of FDG-PET alone were 50% and 78%. Evaluation together with MRT images showed a sensitivity of 50% and a specificity of 86%. CONCLUSION: Sensitivity of FDG-PET in detection of borderline-tumors and early stage ovarian cancer seems to be limited. Low incidence of malignant ovarian tumors requires for assessment of dignity a procedure of high specificity, that is not reached by FDG-PET neither without nor together with MRT images for topographic orientation. Therefore use of FDG-PET for assessment of dignity in suspicious, asymptomatic ovarian tumors is limited.

[Positron-emission tomography of the skeletal system using 18FNa: the incidence, pattern of the findings and distribution of benign changes]. / Die Positronenemissionstomographie des Skelettsystems mit 18FNa: Häufigkeit, Befundmuster und Verteilung benigner Veränderungen.

PURPOSE: We evaluated the frequency, distribution and appearance of benign lesions in 18F-PET scans. METHODS: Between March 1996 and May 1997, 18F-PET scans were performed in 59 patients in addition to conventional planar bone scintigraphy. Eleven patients were subjected to additional SPECT imaging. The main indication was searching for bone metastases (58 pat.). The diagnosis was confirmed radiologically. RESULTS: With 18F-PET in 39 patients (66.1%) 152 benign lesions, mostly located in the spine were detected. 99mTc bone scans revealed 45 lesions in 10 patients. Osteoarthritis of the intervertebral articulations (69%) or of the acromioclavicular joint (15%) were the most common reasons for degenerative lesions detected with 18F-PET. Osteophytes appeared as hot lesions located at two adjacent vertebral endplates. Osteoarthritis of the intervertebral articulations showed an enhanced tracer uptake at these localizations, whereas endplate fractures of the vertebral bodies appeared very typical; solitary fractures of the ribs could not be differentiated from metastases. Rare benign lesions were not studied. CONCLUSION: Most of the degenerative lesions (84%) detected with 18F-PET had a very typical appearance and could be detected with the improved spatial resolution and advantages of a tomographic technique. 18F-PET had an increased accuracy in detecting degenerative bone lesions.

Pharmacokinetics of 99Tcm-pertechnetate and 188Re-perrhenate after oral administration of perchlorate: option for subsequent care after the use of liquid 188Re in a balloon catheter.

Radioactive wires and other linear sources are currently being used in clinical trials as endovascular brachytherapy to prevent restenosis after percutaneous transluminal coronary angioplasty. A new concept is the use of a liquid-filled balloon containing a beta-emitting radioisotope. A major advantage is optimal delivery of the radioactivity to the vessel wall. Rhenium-188 (188Re) is a high-energy beta-emitter that is routinely available from a 188W/188Re generator in liquid form. Since 188Re-perrhenate could be released in the unlikely event of balloon rupture, we investigated whether, in analogy to pertechnetate, subsequent use of perchlorate can reduce the uptake of perrhenate in the thyroid. We performed static (n = 9) and dynamic (n = 11) thyroid scintigraphy with 99Tcm-pertechnetate to estimate the overall reduction in activity within 30 min and the washout from the thyroid after oral administration of 600 mg perchlorate (T1/2). In two patients, 188Re was injected to estimate the whole-body distribution and the discharge of thyroid activity after perchlorate use. Based on MIRD Dose Estimate Report No. 8 (valid for 99Tcm-pertechnetate), the radiation burden was calculated for intravenous administration of 188Re and competitive blocking with perchlorate. In 20 patients, 99Tcm uptake by the thyroid was reduced by 85% within 30 min by perchlorate. The mean (+/- S.D.) washout rate (T1/2) was 8 +/- 2 min in 11 patients. Perrhenate showed a whole-body distribution similar to that of pertechnetate and the thyroid activity could be displaced (T1/2 = 6.3 and 9.3 min, respectively) by oral administration of perchlorate, with reductions in uptake of 83% and 75% within 30 min, respectively. Whole-body scanning demonstrated no regional accumulation of 188Re-perrhenate with excretion by urine. Dose estimates gave an effective dose equivalent of 0.42 mSv MBq-1, which decreased to 0.16 mSv MBq-1 after perchlorate blocking. 188Re has favourable properties for endovascular brachytherapy via a balloon catheter and, in the unlikely event of balloon rupture, whole-body radiation can be reduced to 38% by subsequent oral administration of perchlorate.