IRANIAN JOURNAL OF NUCLEAR MEDICINE
Year:2006 | Volume:14 | Issue:25|Papers Count:10

This paper intends to compare the abilities of the two major imaging modalities in nuclear medicine imaging: Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT). The motivations are many-fold: (i) To gain a better understanding of the strengths and limitations of the two imaging modalities in the context of recent and ongoing developments in hardware and software design; (ii) To emphasize that certain issues, historically and commonly thought as limitations, may now be instead viewed as challenges that can be addressed; (iii) To point out that existing PET and SPECT scanners in the field can (much) benefit from improvements in image-reconstruction software; (iii) To point-out (to engineers, physicists and software-developers) important areas of research in PET and SPECT imaging that will be instrumental to further improvements in the two modalities.

Introduction: Prostate specific antigen (PSA) is one of the most sensitive markers for diagnosis of prostate cancer. Immunoradiometric kit (IRMA) is a common and sensitive method for determination of PSA in clinical laboratories. This kit has four major components: solid phase coated with monoclonal antibody, pair antibody labeled with I-125, series of standards in different ranges of concentration and lyophilized control samples. In IRMA method, PSA is determined in human serum. Therefore, matrix of standards have to be similar to human serum. Using human serum as standard has many shortcomings namely biohazard contamination, instability, serum protein precipitation and unavailability. Artificial matrix however, is an ideal substitute for human serum.Methods: In this study, we used an artificial matrix as standard sample and evaluated its effects including reproducibility, sensitivity, precision and stability for determination of PSA in comparison to human serum.Results: The specificity, sensitivity, storage condition and the stability of these standards prepared with artificial matrix were studied. Similar results in comparison to human serum was observed.Conclusion: The prepared standards with this matrix had suitable and ideal properties and it can be used as standard in PSA assay kit.

Introduction: Leptin, secreted from adipose tissue may have some correlation with coronary artery disease according to some reports in literature. The mean concentration of plasma leptin in patients with normal and abnormal myocardial perfusion imaging (MPI) and relation of leptin levels, independently to abnormality in MPI after correction for body mass index (BMI) was evaluated.Methods: As a cross-sectional study on 270 patients (July-December 2004), data was collected by questionnaire, history and physical examination. After a 12-hours overnight fast, blood samples were obtained. Myocardial perfusion scan was performed and quantitative assessment according to 17 segments analysis was carried out.Results: For 114(42.2%) males and 156(57.8%) females, mean age was 55.8±0.7. Frequency of normal, low and high-risk scans were 101 (37.4%), 67 (24.8%), and 102(37.8%), respectively. Close relationship between BMI and leptin levels was observed (r = 0.42). One-way ANOVA for BMI, leptin, triglyceride, total cholesterol, LDL-C, HDL-C and fasting blood sugar didn't show differences between three groups(p>0.05). Adjusted odds ratio of leptin for BMI in presence of abnormal MPI was 1.05 (0.95, CI: 0.82-1.4).Conclusion: Serum leptin level shows no correlation with coronary artery disease risk category or factors (excluding BMI).

Bone scanning using the 99mTc-phosphate analogs is an established diagnostic modality and a commonly requested radioisotope examination for a variety of pathologies involving the skeleton, such as osteomyelitis, bony metastases, and occult fractures. The bone scan is one of the most commonly requested procedure in most nuclear medicine department. The images show areas of increased and decreased activity usually related to the bone turnover. The bone scan is interpreted by evaluating the pattern of radioactive localization in the skeleton and identifying areas of increased uptake (hot spots) or, less frequently, decreased or absent activity (1). Unfortunately, the findings are most often very nonspecific and do not tell us the exact underlying cause of the abnormal activity. A variety of factors may change the normal distribution of bone-seeking radiopharmaceuticals. Although most of the times these areas of abnormal radiotracer activities are due to true pathologic bone states, however, it is not infrequent that they are caused by technical errors such as urinary contamination, no uniformity of gamma camera, and attenuation of activity by foreign bodies. These art factual causes warrant careful attention to prevent unnecessary interventions. In certain conditions, no osseous structures other than the urinary tract are seen on the bone scan. For example, there may be localized muscle uptake, such as myositis ossificans, or localization in a pleural effusion. Such serendipitous findings may constitute welcome diagnostic information (1). On the other hand, soft-tissue uptake may at times hamper interpretation of the study by bringing in artifacts that degrade the quality of the images. Therefore, recognition of patterns of nonbony uptake is important for correct identification of artifacts and accurate interpretation of the scan (1). This paper presents two cases of art factual causes of odd radiotracer activity in bone scans. In both cases the artifact is at least somewhat related to an indwelling catheter.

Introduction: The mechanism of action and metabolism of clozapine, a complex drug used in psychopharmacology, is not completely understood. The effects of this compound in human body are related to some interactions with serotonin and dopamine neurotransmitter receptors. To further elucidate the mechanism of action and to support ongoing drug metabolism studies, [14C] clozapine with suitable radiochemical purity was synthesized in nuclear research center of AEOI.Methods: In this report radiochemical and chemical purity of [14C] clozapine were determined by liquid scintillation and reversed phase-HPLC respectively. Separation of [14C] clozapine and its synthesized interface products was carried on C8 optimal column and UV detector at 254nm.The mobile phase consisted of acetonitril-buffered aqueous solution of sodium phosphate with a flow rate of 1ml/min.Results: Detection limit and analytical precision of RP-HPLC method were 0.01μg/ml and 1- 3.4% respectively. The chemical purity of synthesized clozapine was >99%. For determination of activity and radiochemical purity, liquid scintillation spectrometer was used and counting was done by direct addition of samples to ACS (Amersham) solution. Specific activity of synthesized clozapine was 10μCi/mg and radiochemical purity of >99. % was achieved.Conclusion: By separation of [14C] clozapine and its synthesized intermediate products the represented methods, in addition to determination of total yield of reaction, it was possible to determine every step of reaction therefore; it was not nessaseray to use classical methods such as: distillation, liquid-liquid extraction, etc. If the HPLC instrument is equipped with radiochemical detector, simultaneous determination of radiochemical as well as chemical yields of products are possible.

Introduction: It has been suggested that calculation of differential renal function (DRF) using 99m Tc-DMSA may lead to overestimation of the function of an obstructed kidney. The aim of this study was to evaluate the effect of diuretic administration on the determination of DRF using 99m Tc-DMSA scintigraphy in patients with dilated pelvis.Methods: Thirty three patients, aged from 2 months to 66 years (19.27±20.83 years, 22 males, 11 females), in whom unilateral hydronephrosis had been documented by ultrasonography and diuretic renography were included in the study. 99mTc-DMSA scintigraphy was performed in all patients 3 hours after tracer injection. Immediately after the standard study, furosemide was injected in all patients, and 30 min later anterior and posterior images were obtained. DRF was calculated for each patient and from each 99m Tc-DMSA study by using the geometric mean method.Results: We did not observe any significant difference in all patients between the DRF values obtained before and after diuretic administration (the DRF value of the affected kidney was thus taken into account)(P=0.35). When we compared DRF values obtained from standard and from diuretic DMSA studies, the mean of the differences was only 0.18% and the SD was only 1.09%. In 17 patients (group1), diuresis renography revealed an obstructive curve pattern while 16 patients (group 2) had a nonobstructive dilated renogram curve pattern. There were again no significant differences between DRF values obtained before and after diuretic injection in each groupConclusion: In view of our study, diuretic administration seems to be an unnecessary intervention because it has no effect on the accuracy of DRF measurements using 99m Tc-DMSA scintigraphy in patients with a dilated collecting system whether it is obstructed or not.

Introduction: In Iran dipyridamole is the main agent used for coronary dilatation before myocardial perfusion SPECT. This study tries to evaluate the side effects after dipyridamole infusion and its relation with hemodynamic changes.Methods: We studied 300 patients who referred to myocardial perfusion scan. The exclusion criteria were: 1) AV block degree 2 or more, 2) Asthma 3) Sick sinus syndrome 4) LV EF<25%. Dipyridamole infusion was done with a dose of 0.568 mg/kg of body weight for 4 minutes and blood pressure and pulse rate were measured before infusion of dipyridamole and 2 minutes after termination of infusion. Patients were asked for any side effects and any complaints were recorded. Relationship between these side effects and age and sex of patients as well as hemodynamic changes were studied.Results: 148 female and 152 male patients studied with a mean age of 55.9 years (11.1). After dipyridamole infusion 79.3% of patients had at least one symptom, with headache (50%) and sweating (3%), the most and the least prevalent symptoms respectively. Mean heart rate increment was 8.8 and 9.2 beat per minute in female and male respectively (P=0.59). Mean systolic blood pressure decrement was 8.5 (8.6) and 9.6 (7.1) mmHg in male and female respectively (P=0.21). Diastolic pressure decrement was 4.6 (6.7) and 6.8 (6.3) mmHg in male and female respectively (P=0.003). Headache and flashing were more frequent in female patients (P=0.004). Other symptoms like dizziness, dyspnea, chest discomfort and abdominal discomfort were not different between female and male patients (P>0.08).Conclusion: After dipyridamole infusion, nonspecific side effects are frequent. Headache and flashing is more frequent in female patients. Flashing is related to decrement in diastolic blood pressure.

Introduction: 99m Tc-MIBI has been proposed for use as an imaging agent for various tumors, including breast cancer, lung cancer, lymphomas, melanomas and brain neoplastic lesions. Brain tumors are very common and radiotherapy being major part of treatment following surgery. After radiotherapy, deteriorating clinical status can be due to either radiation necrosis or recurrent tumor. Computed tomography and magnetic resonance imaging offer imperfect discrimination of radiation necrosis and tumor recurrence.Methods: In this study, 26 patients with primary brain tumors and deterioration of clinical status after radiotherapy were evaluated. 99mTc-MIBI brain SPECT was performed 10 minutes and 3 hours after IV injection of 20 mCi 99mTc-MIBI. The images were obtained with ADAC dual head camera. Transverse, coronal and sagital views were reconstructed.Results: Focal 99m Tc-MIBI uptake was observed in 14 patients. Eight of these patients expired within 6 months. The CT scan was positive in 7 patients and the rest had equivocal or negative results. Of 12 patients with negative 99m Tc-MIBI scan, only 2 patients died during the 6 months follow up. Six of these patients had positive, five had equivocal and one had negative CT scan.Conclusion: Patients with negative MIBI scan, radiation revealed higher survival rate. Focal uptake on 99m Tc-MIBI scan is probably due to recurrent tumor, with lower 6 months survival rate. It can be concluded that brain SPECT scan with 99m Tc-MIBI is a useful method for discriminating radiation necrosis from tumor recurrence in patients following brain radiotherapy.