IRANIAN JOURNAL OF NUCLEAR MEDICINE
Year:2006 | Volume:14 | Issue:26|Papers Count:8

This article is intended to provide an overview of various aspects of clinical PET/CT. These include discussions of:(i) Important areas of clinical application;(ii) Opportunities in clinical research;(iii) Scanner and operating-mode considerations (e.g. BGO vs. LSO, LYSO or GSO scanners, 2D vs. 3D imaging).(iv) Study-specific considerations (e.g. patient preparation and positioning issues, injected dose, use of CT contrast agents).

Introduction: Medullary thyroid carcinoma (MTC) is a rare thyroid cancer secreting calcitonin (CT) which is the most sensitive and specific tumor marker for MTC. This type of thyroid cancer is able to metastasize to different body areas including regional lymph nodes, lungs, liver and bone. The aim of this study was to assess the sensitivity and specificity of [99mTc-DMSA (V)] whole body scan (WBS) in detection of metastases in MTC.Methods: This descriptive and prospective study was performed in 15 patients with MTC referred to our nuclear medicine centre since 2004 to 2005. These patients were compared regarding age, sex, and duration of the disease. Sensitivity and specificity of each diagnostic modality in detection of metastases were calculated and compared statistically.Results: [99mTc-DMSA (V)] showed 91% sensitivity and 75% specificity as compared with serum calcitonin as gold standard. The figures for CT scan were 82% and 45%, respectively. CEA showed 64% sensitivity and 50% specificity.Conclusion: It is concluded that despite the slightly lower sensitivity and specificity of [99mTc- MSA (V)] as compared to calcitonin (Gold-standard method), this radiotracer can be used for identification of recurrence or metastasis of modularly thyroid carcinoma.

Introduction: The relationship between depression and coronary artery disease is well established; however assessment of this relationship using functional and semi-quantitative imaging (myocardial perfusion scintigraphy) was lacking. The aim of this study was to assess the relationship between the severity of depression and the severity of myocardial perfusion abnormality.Methods: Patients were assessed with rest/stress 99mTc-MIBImyocardial perfusion scintigraphy using Single Photon Emission Computed Tomography (SPECT) and Beck Depression Inventory (BDI-H). Visual and semi-quantitative assessment of myocardial perfusion score (MPS) in a five-scale measurement for standard 20-segment-model were used.Results: When all patients (n=167) were evaluated, no correlation was found between MPS and BDI score. Considering only those with significant perfusion abnormality (MPS<90, n=38), negative correlation was found between MPS and BDI score (r= -0.641, p=0.017). Also higher BDI scores were recorded for patients with inferior wall infarction when compared with those with normal or near-normal MPS (MPS>95) (p=0.097), but other myocardial walls failed to show such association.Conclusion: In patients with significant perfusion abnormality, the greater is this abnormality the more severe is the depression. Also patients with inferior wall infarction, have a higher BDI-score as compared with normal subjects.

Introduction: Hemangiomas are the most frequent benign tumors of the liver and detecting them from metastasis or other malignant hepatic tumors is of outmost importance. 99mTc-RBC scan is highly specific and is the method of choice for this differentiation. This scintigraphy is performed in Planar and SPECT modes. These two procedures are in agreement most of the times, however since SPECT is more expensive and time consuming we planned a study to evaluate the agreement of these two methods. Methods: Sixty two patients (age range 20-80 yr, mean age 42 yr), 41 female (67%) and 20 male (33%), who were under evaluation for liver mass detected on abdominal ultrasound or CT scan, underwent 99mTc- RBC scan with both Planar and SPECT methods. The data was processed by computer and SPSS software (11.5).Results: Planar scan was positive in 42% and negative in 59% of cases, while for SPECT study these values were 68.9% and 31.1%, respectively. The Kappa value for planar and SPECT scan results was 48%, and there were 17 lesions (27%) which were detected only by SPECT. SPECT scan defined 35% of the posteriorly located hemangiomas, and 58.3% of hemangiomas smaller than 3 cm, which were not detected by planar scans. Also 75% of patients with multiple hepatic lesions showed more lesions by SPECT as compared to planar scan.Conclusion: Since there is a weak agreement between SPECT and Planar scan, SPECT is considered the more reliable method in diagnosis of liver hemangioma and this is especially true when the hemangioma is of small size, has a posterior location or in cases of multiple lesions.

Introduction: Nowadays, Imaging of the myocardial perfusion (MPI) using the single photon emission tomography (SPET) in the diagnosis of coronary artery disease, especially myocardial ischemia, is of great importance. In contrast to the coronary artery angiography, MPI is non-invasive, less expensive and more physiological. Unfortunately, this image is affected by the some artifacts. These artifacts lead to decrease image diagnostic accuracy and increase false positive cases. One of the most important effective artifacts is due to attenuation. These attenuation artifacts are caused by the left breast tissue in women, diaphragm in men and the chest wall in both sexes. Because of the inherent non- uniform attenuation map in the thorax region, this problem is very complex. Methods: The aim of this study is to correct attenuation artifact with a simple method that is available and very easy to use. In this study we used transmission scanning by 99mTc in the sequential views and an attenuation map was created.After attenuation correction of the original images with attenuation map, non corrected and corrected images were compared with angiography results to apply attenuation correction based on functional findings. Results: Results show that new artifacts are created and experiences of physicians in the impression of the images is critical. Finally, the sensitivity of images increased from 86.20% to 96.42%, the specificity decreased from 85.71% to 54.54% and the diagnostic accuracy decreased from 86% to 78%. Conclusion: Attenuation correction can produce new artifacts, which can influence the way scans are interpreted. It seems that attenuation correction of the images, need special experience. Lack of enough experience in attenuation correction techniques, can comprise the diagnostic accuracy of images.

Introduction: Binding a monoclonal antibody to tumor associated antigens is an effective method for cancer therapy because these agents can specifically target malignant cells, in fact monoclonal antibodies are effective agents for diagnosis, grading and treatment of different kinds of cancers.Methods: In this research, a new monoclonal antibody against colon cancer cells was prepared and antigen concentration in different cells determined by a radioimmunoassay method using iodine (1-125) labeled protein G.Results: 125I-labeledprotein G percent binding to white blood cell, HT29, LS 180 and MCF7 cell lines were 7.1%, 91.2%, 75.8% and 40.2%, respectively.Conclusion: Regarding importance of monoclonal antibody applications, it is necessary to find an efficient method for their evaluation in cancer therapy. In this method, a radioactive agent with no count restriction was used. Also by this method, amount of the antigen can be easily quantified.

Introduction: Using labeled peptides enjoys high importance in nuclear medicine. Somatostatin analogs labeled with different radionuclide are vastly investigated for diagnosis or treatment of somatostatin receptor positive tumors. Labeling somatostatin analogs with 99mTcas alternative of 111 In needs doing different quality control method for determination of labeling yield and complex stability for clinic applications.Methods: For determining radiochemical purity, three different methods were compared and evaluated including HPLC, TLC and Sep-Pak. Results: All the three methods were suitable for determining of radiochemical purity in peptide kits, although using HPLC was more effective rather than the others.Conclusion: HPLC was the best method for determination of radiochemical purity of the peptide kits. TLC or Sep-Pak method should only be employed if HPLC is not available in nuclear medicine clinics, and after training and gaining sufficient operational experience.

Introduction: [18F]-6-thia-14-fluoro-heptadecanoic acid 3b, a free fatty acid, has been used in myocardial PET imaging. In order to establish an automated synthesis module for routine production in the country, a study performed for optimization of the production conditions as well as making modifications.Methods: [18F] Benzyl-14-Fluoro-6-thia-heptadecanoate 2b was prepared in no-carrier-added (n.c.a) form from Benzyl-14-tosyloxy-6-thia-heptadecanoate 1 in one step at 90°C in Kryptofix2.2.2 [18F] and acetonitrile as the solvent followed by Silica column chromatography. The radiolabeled ester 2 was then hydrolyzed to yield [18F]-6-thia-14-fluoro-heptadecanoic 3b. The final solution was concentrated using C18 SPE system and administered to normal rats for biodistribution as well as co-incidence imaging studies.Results: The synthesis took 15 min with overall radiochemical yield of 15-25% (EOS) and chemical radiochemical purity more than 94%. Automation was performed using a two-pot synthesis. The best imaging time was shown to be 140-180 minutes post injection.Conclusions: Using this procedure a fast, reliable, automated synthesis for the cordial PET tracer, i.e. [18F]-FTHA can be obtained without HPLC purification step.