Iranian Journal of Nuclear Medicine
Volume:17 Issue: 1, Winter-Spring 2009

The production and application of PET tracers has been a unique step in the progress of nuclear medicine in last two decades. The most important PET tracers include F-18, C-11 and N-13 radioisotopes and many nuclear medicine centers throughout the globe are using them. However some new tracers are under their way to the mass administration, currently being in the clinical trials or preliminary studies. Gallium-66 and 68 tracers such as Ga-DOTANOC and Ga-DOTANIC are currently being used in many neuroendocrine tumor studies in human in Europe and North America, and global application of these tracers remain to the cheaper and easier providence of 68Ge/68Ga generators. Copper tracers such as 61,62,64Cu-ATSM and 61,62,64Cu-PTSM are the most important unconventional tracers used in hypoxia and perfusion studies respectively using PET technology. Copper tracers can easily be produced using a medium cyclotron with simple chemistry. Many other interesting PET radioisotopes such as Tc-94m (HL. 52 min), I-124 (HL. 100h), Y-86 (HL. 14.7) and rubidium tracers are being studied in some research centers in the world. This review article would describe the properties, mechanisms, production routes and problems of unconventional PET tracers with a look to the future of some important drug candidates

Radio-guided parathyroid surgery along with other minimally invasive surgeries constitutes the main surgical treatment procedures for different kinds of hyperparathyroidism. In this article we have reported our experience of radio-guided parathyroid surgery using Tc-99m sestamibi. Ten patients with hyperparathyroidism included in our study. Twenty mCi of Tc-99m sestamibi was injected intravenously to the patients in the day of surgery. All patients underwent surgery 4 hours after injection of the tracer. Abnormal parathyroid glands were localized by surgical gamma probe during surgery and were removed. Eight out of 10 patients had single adenoma. One patient had parathyroid hyperplasia secondary to chronic renal failure. The one remaining patient had persistent hyperparathyroidism with previous unsuccessful parathyroid surgeries. Except for the patient with parathyroid hyperplasia, parathyroid hormone (PTH) level of all other patients decreased after surgery including the patient with persistent hyperparathyroidism. Minimally invasive radio-guided parathyroid surgery is an easy and safe method for surgical treatment of hyperparathyroidism. With the increasing availability of surgical gamma probes and nuclear medicine facilities in Iran considering this kind of approach for surgical treatment of hyperparathyroidism seems rational.

Bombesin (BN), a 14-amino acid neuropeptide, shows high affinity for the human GRP (gastrin releasing peptide) receptors, which are overexpressed by a variety of cancers, including prostate, breast, pancreas, gastrointestinal, and small cell lung cancer. Aim was to prepare [6-hydrazinopyridine-3-carboxylic acid (HYNIC0), D-Tyr6, D-Trp8] - BN [6-14] NH2 that could be easily labeled with 99mTc and evaluation of its potential as an imaging agent. Synthesis of the peptide amide was carried out onto Rink Amide MBHA (4-Methylbenzhydrylamine) resin. A bifunctional chelating agent (BFCA) was attached to the N terminal peptide in solid-phase. 99mTc labeling was performed by addition of sodium pertechnetate to solution that include [HYNIC0, D-Tyr6, D-Trp8] Bombesin [6-14] NH2, tricine, ethylenediamine-N,N′-diacetic acid (EDDA) and SnCl2. Radiochemical evaluation was carried out by reverse phase high-performance liquid chromatography (HPLC) and instant thin layer chromatography (ITLC). In-vitro internalization was tested using human prostate cancer cells (PC-3) with blocked and non-blocked receptors. Biodistribution was determined in rats. [99mTc/tricine/EDDA-HYNIC0, D-Tyr6, D-Trp8] bombesin [6-14] NH2 was obtained with radiochemical purities >98%. Results of in-vitro studies demonstrated a high stability in serum and suitable internalization. Biodistribution data showed a rapid blood clearance, with renal excretion and specific binding towards GRP receptor-positive tissues such as pancreas. In this study, labeling of this novel conjugate with 99mTc easily was performed using coligand. The prepared 99mTc-HYNIC-BN conjugate has promising characteristics for the diagnosis of malignant tumors.

In patients with thyroid carcinoma, radiation absorbed doses of the thyroid and surrounding tissues is important to weigh risk and benefit considerations. In nuclear medicine, the accuracy of absorbed dose of internally distributed radionuclides is estimated by different methods such as MIRD and direct method using TLD. The aim of this study is using TLD and a phantom to determine the amount of cumulated activity in thyroid and surrounding tissues. Thermoluminescent dosimeter (TLD) measurements were performed on 27 patients on the skin over the thyroid, sternum and cervical vertebra. There were 5 TLDs for each organ which they were taken after 4, 8, 12, 20 and 24 hr. To calculate the amount of activity in the thyroid a head and neck phantom with a source of 10 mCi of 131I was used. Several TLDs were placed putted on the surface of thyroid on phantom (similar to patients) for 24 hr and then compared the dose of phantom and patients followed by calculation of the activity in patient''s thyroid. TLD measurements showed cumulated radiation absorbed doses (cGy) of 315.6, 348.1 and 361.9 for thyroid with administration of 100, 150 and 175 mCi of 131I, respectively. For sternum the values found to be 201.5 cGy, 275.2 cGy and 242.6 cGy. For cervical vertebra results were 311.5 cGy, 184.1 cGy and 325.9 cGy. The average of measurements was 33.3 cGy using of TLDs on phantom and absorbed activity in thyroid were 94.9, 104.6 and 108.8 mCi in 24 hr for mentioned doses administration. In this work a method to obtain the absorbed activity in the thyroid and other surrounding tissues is described. By this method, the amount of 131I needed for each patient also could be determined. The results of this work can be used in estimation of absorbed dose in thyroid and other organs using of MIRD method.

It seems that demographic and clinical features of patients referred for myocardial perfusion scintigraphy (MPS) is different among populations and healthcare settings. The purpose of the current study is to evaluate the clinical features and risk factors of patients referred for myocardial perfusion scintigraphy to a military hospital. As a cross-sectional study, the clinical and laboratory data of all patients who were referred for MPS were recorded. MPS was performed using 99mTc-Sestamibi or Thallium-201 (Tl-201) as the radiotracer. From March 2005 to March 2006, the data of 1392 consecutive patients were recorded. The mean age of the patients was 55.3±14.8 years. 45.6% of the patients had no major risk factor, while 38.5% had one and 15.9% had two risk factors. Hypertension was the most common risk factor, while cigarette smoking was reported by eight percent of the patients. The method of stress protocol was dipyridamole infusion in 69.2%, Treadmill exercise test in 28.4% and dobutamine infusion in 2.4% of the cases. The sensitivity, specificity, positive predictive value, negative predictive value and overall accuracy of MPS in detection of angiographically positive CAD were 88.5%, 71.4%, 94.3%, 46.8% and 75.3%, respectively. In our population hypertension is the most frequent risk factor, so extensive social programs should be implemented aiming at controlling this variable, in order to prevent its possible cardiac complications. Cigarette smoking is less common than general population, which could be due to social characteristics of the target community and their beliefs, so this distinctiveness should be well defined and promoted. The differences in the pattern of cardiovascular symptoms and risk factors can be considered as indirect evidences to the fact that the pattern of referral for MPS in our country is significantly different from those in developed countries, a fact that warrants further evaluation in order to confirm its appropriateness based on the validated international guidelines.

Evidence Based Medicine (EBM) is a new approach to patient management which incorporates best evidence with the clinical expertise of the health care providers. Although this approach has had a rapid growth in many clinical disciplines, its applications in radiology and nuclear medicine has not been addressed sufficiently. In this review EBM is briefly explained and the first two steps of the evidence based practice are described.

A 36-year-old woman with right upper quadrant abdominal pain since three months previously and no other significant medical history was referred for evaluation of an abdominal mass. Upon clinical examination, a large palpable mass in the mid -upper abdominal area was noted. Abdominal ultrasound and spiral CT-scan showed a large hepatic mass in the left liver lobe. The patient was referred for Tc-99m labeled RBC scintigraphy to assess the possibility of presence of liver hemangioma. The radionuclide imaging confirmed the diagnosis of hemangioma which in this case, the huge size of the lesion was of interest.