IRANIAN JOURNAL OF NUCLEAR MEDICINE
Year:2003 | Volume:- | Issue:20|Papers Count:11

Determination of the total body absorbed dose consists of two parts: Beta radiation absorbed dose and gamma radiation absorbed dose. The first part is generally determined by clinical data, while the second part has a parameter called absorbed ratio and is determined by computational methods. The Monte-Carlo computational methods have been shown to be the most suitable in determination of the absorbed dose ratio. We employed the Monte-Carlo code MCNP-4A and calculated the absorbed ratio for the whole body and thyroid gland. We used a distributed source of I-131 and calculated the absorbed ratio for emitted photons in different energies from this source. The phantom was an ellipsoid having the human body dimension. Water and material similar to body tissue were chosen as the phantoms filling materials. Results of calculation were compared with Brownell works and the differences were acceptable. To check the accuracy of calculation, the phantom was divided into 5×5×5 cm cells and a complete symmetry in the absorbed dose within phantom was observed. The MCNP relative error was reduced to less than 1% by choosing more than 50,000 histories and applying variance reduction techniques

A 65 years old male presented with abdominal pain (R.U.Q) and constipation, associated with weight loss and anorexia since 40 days prior to admission. Serum biochemical tests were normal. Colonoscopy showed hemorrhagic polypoid lesion in the cecum. Barium enema revealed filling defect in the cecum. Sonography revealed a target-shaped lesion (3cm×2.5cm) in upper segment of the right hepatic lobe. CT scan confirmed the same finding as a hypo dense lesion. Following segmental resection of the cecum, pathology indicated the presence of the carcinoid tumor. For better evaluation, ¹³¹I-MIBG scintigraphy was carried out, demonstrating tracer avid metastatic lesions in the right and left hepatic lobes. A review of the series reported in the literature shows that approximately 50-60% of carcinoids are able to concentrate radio labeled MIBG. MIBG uptake apparently correlated with the urinary excretion of 5-HIAA, although this is not a universal finding. The most frequently occurring midgut carcinoids probably concentrate radiolabeled MIBG more readily than those in the hindgut and foregut. Primary and residual tumors are sometimes visualized, but the most striking imaging is that of carcinoid metastases in the peritoneum and liver (Provided that SPECT images with ¹²³I-MIBG or alternatively ¹³¹I-MIBG delayed scans are performed). Lymph node involvement, bone deposits and ovarian metastases have been reported as well. When radio iodinated MIBG and somatostatin scintigraphy results are compared, somatostatin scintigraphy shows a better sensitivity (>80%) in detecting both primary and metastatic lesions. These radiopharmaceuticals play complementary roles in that each give unique information concerning possible treatment either with octreotide or ¹³¹I-MIBG, or both. MIBG imaging cannot generally be relied upon either to detect a carcinoid, or to rule out the disease. When a tumor is strongly suspected of being a carcinoid however, the test can be worthwhile for the following reasons: 1) To disclose any residual/recurrent tumor, in the event that it is not shown by other techniques. 2) To better define the staging. 3) As a prelude to 131-MIBG therapy.

Introduction: Hyperthyroidism is a relatively common disorder caused by different etiologies. Graves disease, and toxic-nodular goiter (Plummer’s disease) are among the most common causes. Treatment with radioiodine is considered to be the treatment of choice in many of the patients. Higher biological half-life of ¹³¹I in hyperthyroid patients as compared with patients with differentiated thyroid carcinoma who have undergone thyroidectomy, may lead to a higher frequency of complications with radioiodine at similar dosage. Therefore gonadal dysfunction in hyperthyroid patients treated with radioactive iodine is not unlikely. Material and Methods: Hyperthyroid patients with the clinical diagnosis of Graves disease, toxic multimodal goiter and toxic adenoma were entered the study. Their age distribution was 16-40 years in women and 17-60 years in men (Reproductive years). Patients were euthyroid at the time of radioiodine treatment. FSH, LH, testosterone and semen analysis in men; and FSH, LH, estrogen and progesterone in women were measured before and 3 months after radioiodine therapy. All patients with previous history of radioiodine treatment, those with known sexual hormone abnormalities, women with a history of tube ligation and men with a history of vasectomy, as well as those women who were receiving OCP contraception were excluded from the study. Results: From 104 enrolled patients, 40 (38.5%) were men and 64 (61.5%) were women. The cause of hyperthyroidism was Graves disease in 66 cases (63.5%), toxic multimodal goiter in 28 cases (26.9%) and toxic adenoma in 10 others (9.6%). Hormonal status was normal in all patients before therapy while this became abnormal in 20 (19.2%) of patients after treatment. Semen analysis became abnormal in 8/20 (40%) of the patients after treatment. Conclusion: Among different variables which were analyzed during study, meaningful correlation was found in the following situations: FSH values in men and women were found to be increased after radioiodine treatment (P<0.0001), sperm count decreased from 124000000 to 62000000 (P<0.0001), the difference in semen analysis changes was also meaningful in men among two different age groups (=<35, >35) (P=0.003) and changes in hormonal status in women in two different age groups (=<30, >30) were found to be statistically significant (P=0.015).

According to the importance of positron emitters in nuclear medicine, 82mRb was produced as a member of this group of radiopharmaceuticals. After being converted into an inject able form, enough information was provided for imaging with this radiopharmaceutical. 82mRb with high radio isotopic purity and half-life of 6.5 hours, in chloride form, can be considered as a suitable positron emitter for the assessment of myocardial function. As a result of the bombardment of 82Kr with 15.4 MeV protons, the activity of 35.04 mCi was finally achieved. The nuclear reaction efficiency was 6.37 mCi/µAh. The product had a high radiopharmaceutical purity, according to international standards

SPECT detects γ-rays from administered radiopharmaceutical within the patient body. γ -rays pass through different tissues before reaching detectors and are attenuated. Attenuation can cause artifacts; therefore different methods are used to minimize attenuation effects. In our study efficacy of Chang method was evaluated for attenuation purpose, using a custom made heart phantom. Due to different tissues surrounding heart, attenuation is not uniform more over activity distribution around heart is also non-uniform. In Chang method, distribution of radioactivity and attenuation due to the surrounding tissue is considered uniform. Our phantom is a piece of plastic producing similar SPECT image as left ventricle. A dual head, ADAC system was used in our study. Images were taken by 180° (Limited angle) and 360° (Total rotation). Images are compared with and without attenuation correction. Our results indicate that Chang attenuation correction method is not capable of eliminating attenuation artifact completely in particular attenuation effects caused by breast.

Gamma-scintigraphy is applied extensively in the development and evaluation of pharmaceutical delivery systems, particularly for monitoring formulations in the gastrointestinal and respiratory tracts. The radiolabel ling is generally achieved by the incorporation of an appropriate radionuclide such as technetium-99m or indium-111 into the formulation or by addition of a non-radioactive isotope such as samarium-152 followed by neutron activation of the final product. Drug delivery systems can be tested in vitro using various techniques like dissolution rate. Since in vitro testing methods are not predictive of in vivo results, such systems should be evaluated in vivo using animal models, especially oral dosage forms. Altered gastrointestinal transit due to individual variation, physiologic or pharmacologic factors, or the presence of food may influence bioavailability. Disintegration or drug release may be premature or delayed in vivo. Similarly, altered deposition or clearance from other routes of administration such as nasal, ocular or inhalation may explain drug absorption anomalies. Therefore, there is a growing tendency for new drug delivery systems to be tested, whenever possible, in human subjects, in a so called phase 1 clinical evaluation. Gamma-scintigraphy combined with knowledge of physiologic and dosage form design can help to identify some of these variables. The resulting insight can be used to accelerate the formulation development process and to help to ensure success in early clinical trials

Post stroke dementia is one of the most common complications of stroke that is preventable and relatively treatable too. The purpose of the study is comparison between the positive findings in brain CT scan and brain perfusion SPECT. 15 patients who were complicated by dementia after cerebrovascular accident and also 5 patients as a control group enrolled in this study. Brain CT scan and brain SPECT were performed during at most one week after stroke. Abnormal findings in both brain CT scan and SPECT were seen in 46% of patients. Brain CT scan disclosed more abnormal findings compared to brain SPECT (33.3%). While brain SPECT findings were more informative than brain CT scan (20%), this study is indicating that brain CT scan and brain SPECT concomitantly are complementary for each other in better diagnosis of post stroke dementia. We did not find any specific diagnostic pattern in brain SPECT of patients suffering from post stroke dementia. The low quality of brain SPECT in spite of uniformity of Gamma camera may be suggestive of low quality of Iran produced ECD kit that needs further evaluation.

Introduction: Renal dynamic study is a well-established and popular test in routine practice of nuclear medicine. The test is non-invasive, rapid and unique in evaluation of the kidney function. In despite of its clinical values, the parameters derived from renogram are physiologically meaningless. That is due to the fact that renogram is not the true kidney function. From mathematical points of view, renogram is the convolution of kidney function and kidney input function. The real kidney function, which is usually called Impulse Retention Function, could be derived using disconsolation technique. The main parameters that can be derived from IRF are transit times. Methods and Materials: The data collected from 30 normal healthy individual volunteers were used for calculation of transit times. Due to sensitivity of the disconsolation technique to the error and to minimize the error in the raw data, an investigation was launched to determine the most suitable method of noise reduction, background subtraction and numerical method of disconsolation. Based on our finding, a software package was developed on the system and evaluated using software phantom. Results: Our results shows that among different transit time parameters for different parts of the kidney, mean transit time of the parenchyma is statistically the most valuable parameter. Assuming a Gaussian distribution for the parameter and accepting a 95% confidence interval, the normal rage of mean parenchyma transit time was calculated to be "205±70 Sec". Using the same logic, the abnormal rage of mean parenchyma transit time was calculated to be more than 300 sec. Discussion: During the last decade, skeptical questions have raised about the suitability of renogram for disconsolation and validity of transit time parameters. Our experiences have proved that kidney is approximately a linear and stationary system, therefore suitable for disconsolation. The validity of transit time parameters is extremely depended on the validity of software being used. Commercial software usually dont have sufficient accuracy for calculation of transit times.