Prediction of changes in left ventricular ejection fraction after off-pump coronary artery bypass grafting surgery by myocardial perfusion single-photon emission computed tomography

Introduction: Left ventricular ejection fraction [LVEF] is considered to be the single most important prognostic factor in patients with previous myocardial infarction. LVEF is not improved in all patients after coronary artery bypass grafting [CABG]. This study aimed to assess the possibility of prediction of LVEF changes after CABG using myocardial perfusion gated signle photon emission computed tomography [GSPECT]

Materials and Methods: Overall, 48 patients with mean LVEF of 30.2% [ +/- 4.7] underwent Echocardiography and GSPECT after injection of Tc-99m-MIBI at rest. Myocardial uptake was evaluated in 17 myocardial segments and was compared with age and gender matched normal data pool. The risks and benefits of CABG were explained to the patients and 16 cases [15 male and 1 female] with the mean age of 61.1 years [ +/- 10.8] accepted to undergo off-pump CABG. All the patients were followed-up for at least six months and echocardiography and GSPECT were repeated at the end of follow up

Results: The mean LVEF was increased from of 31.1% [ +/- 3.5] to 34.5% [ +/- 3.6] after surgery [P<0.001]. Delta LVEF was defined as ?LVEF=LVEF [before CABG] -LVEF [after CABG]. ?LVEF was within the range of 0-8% with the mean of 3.4% [ +/- 2.5]. The number of non-viable myocardial segments was not significantly different between patients with ?LVEF ? 5% and those with smaller changes. Myocardial perfusion was estimated for all segments, and the mean global uptake was defined by adding the mean uptake in all segments, divided by 17. The mean global uptake was 53.1% in our patients. Regression analysis revealed that ?LVEF after CABG can be predicted reliably using the following formula: ?LVEF= -33.8 + [0.77 × mean global uptake] [P<0.01]

Conclusion: Our study showed that change of LVEF after CABG can be predicted reliably using mean global uptake in preoperative myocardial perfusion SPECT at rest

Sentinel node mapping in vulvar cancers: report of two cases and literature review

Vulvar cancer is a rare gynecological malignancy with mainly lymphatic spread. Sentinel node mapping plays an important role in the management of this gynecological malignancy. In the current study, we reported our experience in sentinel node mapping of vulvar cancer and review the literature accordingly. Since the introduction of sentinel node mapping to the surgical oncology community of our university in 2004, we had two operable vulvar cancer patients who were candidate for sentinel node mapping for inguinal lymph node staging. In the current study, we reported these two cases in details and a brief review of literature on sentinel node mapping in vulvar cancer was done. We specifically discussed the overall accuracy, importance of blue dye injection, learning curve effect, frozen section, excisional biopsy and location of the tumors. Overall sentinel node mapping is a safe and effective method for inguinal lymph node staging in vulvar cancers. In order to perform sentinel node mapping efficiently, paying attention to the details is of utmost importance

Gated [99m]Tc-MIBI myocardial perfusion SPECT in patients with right bundle branch block but without evidence of coronary artery disease

We aimed to investigate the effect of right bundle branch block [RBBB] on perfusion and functional parameters in dipyridamole stress/rest Tc99m-MIBI gated myocardial perfusion SPECT [GSPECT] which may be helpful in interpretation of myocardial perfusion imaging. We studied 73 patients with low pre-test likelihood of coronary artery disease in two groups: 38 patients with RBBB and 35 subjects with normal ECG. Both groups underwent two-day dipyridamole stress-rest Tc99m-MIBI GSPECT. Two groups were matched. There was no significant difference in sex and age variable between two groups. Visual calculated SSS and SRS in all patients were between 0 and 3. Regarding the prone images, diaphragmatic attenuation and breast attenuation, all patients GSPECT findings were within normal limits. There was no significant difference in TID ratio between two groups: RBBB group: TID ratio= 1.02 +/- 0.16 and control group: TID ratio= 0.96 +/- 0.14 [P=0.09]. There was no significant difference in left ventricular end-systolic volume, end-diastolic volume, ejection fraction, summed stress and rest motion and thickening scores between RBB patients group and control group. No regional LV wall motion abnormality was noticed in any patient in either group. High normality rate of the LV myocardial perfusion and functional indices in the presence of RBBB was noticed in gated Dipyridamole stress/rest Tc-99m sestamibi myocardial perfusion SPECT. No remarkable false positive perfusion findings or abnormal LV functional indices acquired by GSPECT in this group of patients

Gated myocardial perfusion SPECT in patients with left bundle block but having low probability of coronary artery disease; as compared to the patients with normal electrocardiogram

We aimed to investigate of effect of left bundle branch block [LBBB] on perfusion and functional parameters in dipyridamole Tc99m-MIBI gated myocardial perfusion SPECT which may be helpful in interpretation of myocardial perfusion imaging. We studied 70 patients with low pre-test probability of coronary artery disease in two groups: 35 patients with LBBB and 35 subjects with normal ECG. Both groups underwent two-day dipyridamole stress-rest Tc99m-MIBI GSPECT. From 35 patients with LBBB, 6, 12, and 3 patients had reversible, fixed and partially reversible defects respectively. In 35 patients with LBBB, 8 [22.9%], 6[17.1%] 15[42.9%] and 10 [28.6%] patients had perfusion defects in the apicoseptal, mid-anterior segments, mid-anteroseptal and mid-inferoseptal segments respectively. There was significant difference in TID ratio between two groups: LBBB group: 1.07 +/- 0.21 and control group: 0.96 +/- 0.14 [P=0.01]. There was a significant difference in end systolic volume and ejection fraction between LBBB patients group and control group, while no significant difference was noticed in end-diastolic volume. Nineteen, 14 and 2 from 35 patients with LBBB had normal LV wall motion, paradoxical septal wall motion, and septal hypokinesia, respectively. False positive septal, anterior and apicoseptal perfusion abnormalities are frequently seen on Tc99m-MIBI GSPECT, in patients with LBBB without CAD. Moreover reversible defects are frequently seen with Tc99m-MIBI. Even Tc99-MIBI and vasodilator stress do not increase diagnostic accuracy to clinically useful levels. Lower systolic performance and higher TID ratio could be seen in these patients

Clinical value and severity of myocardial perfusion defects in asymptomatic diabetic patients with negative or weakly positive exercise treadmill test

Although coronary artery disease [CAD] is the leading cause of death in type 2 diabetic patients, it is frequently asymptomatic. Myocardial perfusion imaging [MPI] is reported to show ischemia in a significant number of asymptomatic diabetic patients. We studied the prevalence and severity of myocardial perfusion defects in asymptomatic diabetic patients and its clinical impact. One hundred thirty consecutive asymptomatic patients, aged 35-65 years with type 2 diabetes mellitus and with no history of CAD and no cardiac symptoms were recruited in the study. Echocardiography, electrocardiography [ECG], routine laboratory tests and exercise treadmill test [ETT] were performed and patients with weakly positive or negative ETT underwent Dipyridamole MPI. Patients with positive ETT were referred to coronary angiography. Patients were followed for at least 17 months [mean 21.7 months] and any cardiac event was recorded. We studied 81 female and 49 male patients with mean age of 51.8 years. Negative, weakly positive and positive ETT result was noted in 74.3%, 15% and 10.7% respectively.75% of patients with positive ETT had coronary artery disease in angiography. Gated myocardial perfusion SPECT was done in 106 patients. MPI showed reversible defect in 26.9% of the patients with a mean summed stress score of 3.3 +/- 1.8. Follow up completed in 112 patients and only one patient with abnormal MPI underwent coronary angiography followed by PTCA. No cardiac death, MI, UA or hospital admission occurred among our patients during follow up [17-26 months]. Mean stress end diastolic volume [EDV] was significantly higher in patients with reversible defect compared to patients without reversible defect based on MPI findings [62.0 +/- 31.6 Vs 48.5 +/- 18.4 ml, P=0.04]. Blood glucose and HA1c were significantly higher in patients with ischemia compared to patients without ischemia [P<0.05]. Meanwhile the ratio of TG to HDL was 6.06 +/- 3.2 in ischemic patients compared to 4.8 +/- 2.3 in normal subjects [P=0.03]. Reversible defects are commonly seen in myocardial perfusion SPECT in asymptomatic diabetic patients and are mild in severity and not associated with adverse cardiac events. Routine approach for detection of CAD beginning with ETT seems to be appropriate in these patients

Treatment efficacy of 153Sm-EDTMP for painful bone metastasis

Involvement of the skeleton can cause an excruciating pain in two-thirds of terminal patients with a history of malignancy. Due to several limitations of other therapies, such as analgesics, bisphosphonates, chemotherapy, hormonal therapy and external beam radiotherapy; bone-seeking radiopharmaceuticals have an important role in palliation of pain from bone metastases. Although these kinds of therapies have many advantages including the ability to treat multiple sites of tumoral involvement simultaneously, no significant confliction with other treatments, ease of administration and the potential to be used repetitively; in Iran using of this modality is not widely practiced. In this study we evaluated the clinical usefulness of Sm-153 lexidronamfor pain management of bone metastases. 28 patients [14 males and 14 females] aged 38-77 years with a history of painful bone metastases caused by different cancers, not responding to conventional treatments were included in the study. All patients had a recent whole body bone scan indicating multiple bone metastases. 1 mCi/Kg Sm-153 lexidronam was injected intravenously to the patients. Whole body scintigraphy was done 3 or 18 hours post injection. Pain relief and quality of life have been evaluated by analog pain scale and Karnofsky index every week, respectively. Also, all patients were evaluated for hematological toxicity every two weeks. Active follow ups were performed. 43% of patients showed the presence of the flare phenomenon during the first three days after Sm injection with a mean duration of 2.2 days. The pain relief began between 2 and 16 days post injection and the duration of pain palliation was in the range of 4 to 32 weeks [mean +/- SD=15.22 +/- 7.8].64.3% of patients showed complete relief of pain and 21.4% achieved partial response to therapy. [Over all response to therapy was 85.7%]. The lowest amount of peripheral blood cells was detected in the fourth week for RBCs and in the 6th week for WBCs and PLTs. No one experienced hematological toxicity induced problems. Sm-153 lexidronam is an effective treatment for painful bone metastases. The complication rate is low and the quality of life of the patients after treatment would be significantly improved

Ectopic papillary thyroid carcinoma in the mediastinum without any tumoral involvement in the thyroid gland: a Case report

Ectopic thyroid tissue results from abnormal embryologic development and migration of the thyroid gland. True malignant transformation in ectopic thyroid tissue is extremely rare and is always diagnosed after surgical excision of the lesion by pathology examinations. There are well-documented cases of ectopic thyroid cancer while primary tumoral lesion occurs in the orthotopic thyroid, but only rare cases of ectopic PTC without any evidence of occult thyroid cancer in the orthotopic thyroid or cervical lymph nodes have been reported. We report on a 39 year old woman who was operated for a mediastinal mass. The initial diagnosis was a malignant thymic lesion, which was later confirmed to be a papillary thyroid carcinoma. Consequently, total thyroidectomy was performed and pathology report showed normal thyroid tissue with no evidence of any neoplastic involvement. Until now, only one similar case has been reported

role of nuclear medicine in the diagnosis and management of solitary pulmonary nodules

Solitary pulmonary nodule [SPN] is a frequent finding on the chest x-ray and computed tomography. Nuclear medicine techniques play an important role in the diagnosis and management of SPN. In the current review, we briefly will explain the different nuclear medicine modalities in this regard including positron emission tomography [PET] using 18-F-FDG, and 11-C-Methionine, and single photon emission computerized tomography [SPECT] using somatostatin receptor scintigraphy, 201-Thallium, and 99m-Tc-MIBI

Sentinel node detection failure due to defective labeling and large particle size of Tc-99m antimony sulfide colloid

Many radiotracers have been used for sentinel node mapping with acceptable results. The main difference between these radiotracers is the particle size. In the current study, we reported defective labeling of Tc-99m antimony sulfide colloid which resulted in large particle size. Tc-99m-Antimony sulfide colloid was used for axillary sentinel node mapping of 45 breast cancer patients. The prepared kits were turbid and were used for the first 15 patients. For the remaining 30 patients, we used a filter [GyroDisc CA-PC Cellulose Acetate Membrane; 30 mm; Pore size: 0.2 micro m] after labeling to remove the possible large particles of the prepared kits. On the lymphoscintigraphy images, at least one sentinel node could be identified in 5 and 29 patients of the unfiltered and filtered groups respectively [p=0.00001]. Sentinel node detection by gamma probe was successful in 5 and 30 patients in the unfiltered and filtered groups respectively [p=0.000001]. Tc-99-Antimopny sulfide colloid is a suitable radiotracer for sentinel node mapping of the breast cancer patients. In case of any unusual turbidity of the labeled kit, it should not be used or at least be filtered before injection

Can gallbladder ejection fraction measured by fatty meal cholescitigraphy diagnose chronic cholecystitis?

Despite presence of a body of evidence in support of high accuracy of cholecystokinin cholescintigraphy [CCK-CS], for diagnosis of chronic cholecystitis[CC], some authors have claimed that gallbladder ejection fraction [GBEF] has poor predictive diagnostic values. The purpose of this study was to determine if there is any difference in GBEF between normal individuals and patients with CC. In a prospective case-control study, we studied 36 subjects as control group who did not have any abdominal symptoms, or history of abdominal disease or gallstone. Patients group were 42 with established choronic calcalous cholecystitis[CCC] who complaining of chronic biliary-like pain and had gallstone on ultrasonography. All subjects underwent gallbladder scintigraphy and GBEF was calculated at 30 and 60 minutes after fatty meal [FM] ingestion. In control group GBEF at 30-minute and at 60-minute after FM ingestion were 69.54% +/- 21.04% and 84.26% +/- 11.41% respectively while in patients group GBEF at 30-minute was 61.21% +/- 16.01% and at 60-minute was 80.22% +/- 12.57%. No significant difference was noticed between control and patient groups. GBEF didn't show significant difference between different groups based on the number of gallbladder stone, severity of chronic inflammatory [lymphoplasma] cell infiltration, wall thickness and evidence of fibrosis in the gallbladder wall. Our data are against the diagnostic value of the GBEF as measured by FM-CS in the workup of patients with CC. Thus, interpretation of GBEF should take the proper clinical context into consideration

Comparison between early and delayed images of [67]Ga scintigraphy for evaluation of recurrent lymphoma

Despite widespread use of [67]Gallium for lymphoma evaluation, timing of imaging after injection is a matter of controversy and to the extent of our knowledge no direct comparison has been made between early and delayed gallium images. We aimed to compare 24 and 48 hours post injection planar gallium imaging for evaluation of lymphoma recurrence. 255 patients suspicious of recurrent lymphoma were included in the study. Twenty four and 48 hours post injection [10 mCi] whole body Gallium imaging was performed. Semi-quantitative evaluation [background corrected] was carried out in positive whole body [67]Gallium scans. Diagnosis of recurrence was made by combination of clinical or pathologic examination if possible. In 59 patients the final diagnosis was made by tissue biopsy. In case of uncertain diagnosis, follow up of the patients [mean duration of 13 months] was used. The diagnosis was finally made by the referring hematologist. Whole body gallium scintigraphy was positive in 115 out of 150 patients with recurrence [sensitivity of 76%]. Comparison of the 24 and 48 hour images did not show any new lesion in the 48 hour images. However, delayed 48 hours images were required for definite detection of the gallium avid lesions in the abdominal and pelvic areas in 40 patients. Semi-quantitative evaluation of the lesion showed higher lesion to background ratio for 48 compared to the 24 hour images [p<0.001]. Considering higher lesion to background activity in the 48 hour images, delayed whole body [67]Gallium imaging may be more desirable for diagnosis of recurrent lymphoma, however 24 hour images may be sufficient. Delayed imaging can be reserved for suspicious activities [such as in abdominal images]. The strategy can save time and is more convenient for the imaging centers

Echocardiographic left ventricular functional changes in acute hypothyroidism vs. subclinical hyperthyroidism in patients with differentiated thyroid carcinoma

In order to assess echocardiographic left ventricular functional indices in patients with differentiated thyroid carcinoma [DTC], after L-T4 withdrawal [short-term overt hypothyroidism] and during TSH suppressive therapy, we have evaluated cardiac hemodynamics in a single cohort study. 24 patients with DTC were studied in two phases: 1: at least 4 weeks after L-T[4] withdrawal, 2: at least 8 weeks after beginning TSH suppressive therapy. All patients underwent conventional, Doppler and tissue Doppler echocardiography. Although early diastolic mitral inflow velocity [E wave] [p=0.033], and early diastolic velocity of mitral annulus [E[m]] [p<0.001], were lower in overt hypothyroidism, there were no differences among left ventricular [LV] Dimensions, LV mass and LV mass index, LV Ejection fraction, late diastolic mitral inflow velocity [A wave], E/A ratio, deceleration time [DT], peak systolic velocity of mitral annulus [S[m]], late diastolic velocity of mitral annulus [A[m]], E[m]/A[m] ratio between the two phases. Pulse rate [p<0.001], LV end diastolic volume [p=0.011] and LV end systolic volume [p=0.003] were higher, while QTc Interval was shorter [p <0.001] during TSH suppressive therapy. E/E[m] ratio and pulmonary capillary wedge pressure [p=0.042] were higher in hypothyroidism phase. Three patients developed mild pulmonary artery hypertension and 2 of the patients had mild pericardial effusion during TSH suppressive therapy. Short-term overt hypothyroidism or L-T4 suppressive therapy in patients with DTC may have undesirable cardiovascular effects. So in patients with known history of cardiovascular abnormalities, the caring physician should be aware of the cardiovascular complications during hypothyroidism or suppressive therapy

Coronary artery calcium [CAC] score - a prognostic tool in coronary artery disease?

The aim of this study was to evaluate the impact of measurement of coronary artery calcification score [CAC] in patients with suspected coronary artery disease [CAD] and a normal myocardial perfusion scan. In a prospective study we measured the calcium score of 74 patients [29 m, 45 f, mean age 58.7 [m] and 64.4 [f]] with suspicion of CAD and a normal perfusion scan. In all patients a pharmacological stress scintigraphy and calcium scoring were performed on a T6 Symbia gamma camera [Siemens, Knoxville, USA]. Attnuation correction was performed using a low dose CT. the mean total CAC score was 182.6 +/- 435.7 and ranged from 0-2309. 21/29 of the male patients [72%] and 17/45 of the female patients [38%] had an Agatst on score of >10. There were 9 cases [5m, 4f] with a calcium score of >400 and 3 cases [2m, 1f] with a calcium score >1000. No cardiac event was noted in these cardiac death of a patient with total Agatston score of 278. Seven patients also underwent angiography because of their clinical symptoms, 4 of which [57%] had an elevated Agatston score. Our study showed that calcium score measurement accompanied with SPECT imaging is feasible in routine myocardial perfusion imaging with SPECT/CT machines. Calcium score measurement in patients with normal stress myocardial perfusion scintigraphy, may be useful in risk stratification of the patients. Further prospective studies with larger patient numbers and longer follow-up time are needed to find out the impact of this advantage by hybrid imaging

Sentinel lymph node biopsy in melanoma patients: an experience with Tc-99m antimony sulfide colloid

Sentinel lymph node biopsy is the standard procedure for lymph node staging in intermediate thickness melanoma. In Iran, this procedure has not been addressed sufficiently. In this study, we report our experience in this area. Ten consecutive patients with intermediate thickness melanoma where included in our study. 1.5 mCi of Tc-99m antimony sulfide colloid in two divided dose was injected around the tumor. All patients underwent surgery 2-4 hours after injection of the tracer. Patent blue V dye was also used for 8 patients. Using a hand-held gamma probe, the sentinel nodes were harvested and sent to the pathologist for frozen section and H and E review. For patients with positive sentinel nodes, lymph node dissection was performed. At least one sentinel node could be harvested in all patients. The mean number of sentinel nodes was 1.66. Detection rate with radiotracer and blue dye was 100% and 75% respectively. 30% of the patients had positive sentinel nodes. One patient in the pediatric age range and one head and neck melanoma were included in our study with successful sentinel node mapping. Sentinel lymph node biopsy using Tc-99m antimony sulfide colloid is a reliable and safe method in melanoma patients which can help in treatment planning and patient's ultimate prognosis

Sensitivity of gallium scintigraphy for evaluation of recurrent lymphoma: comparison of planar and SPECT imaging

Although PET scanning using F-18[FDG] is considered the superior radiotracer for tumor imaging, Gallium-67 is still in use for some malignancies such as lymphoma and hepatoma. One of the strategies to improve the diagnostic accuracy of Gallium is to perform SPECT which is reported to be more sensitive compared to planar imaging. In this study we compared the sensitivity of SPECT and planar imaging in patients suspicious of thoracic recurrent lymphoma. 129 patients with suspicious recurrent lymphoma of the thorax were included into the study. All patients received 10mCi Gallium-67-citrate intravenously. Twenty four and 48 hours post injection whole body and thoracic SPECT imaging was performed. The final diagnosis of recurrence was achieved by combination of clinical and imaging findings or pathologic examination whenever possible. The final diagnosis of 83 [64.3%] patients was recurrence of lymphoma in the thoracic area and the remainder 46 [35.7%] were in remission. The sensitivity of planar and SPECT imaging for diagnosis of recurrent lymphoma was 63% [[52-73%] with 95% confidence intervals] and 87% [[79-94%] with 95% confidence intervals], respectively. In our study, 20 patients with the final diagnosis of lymphoma recurrence in the thoracic area had negative planar despite positive SPECT imaging. This showed an increase of 24% in sensitivity of the scan [from 63% to 87%] by adding SPECT imaging to the procedure. Our recommendation is integrating SPECT modality into all gallium scintigraphy for lymphoma recurrence

Minimally invasive radio-guided surgery for hyperparathyroidism: an experience with Tc-99m sestamibi

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

Normal values of left ventricular functional indices in gated [99m] TC-MIBI myocardial perfusion SPECT

Although left ventricular[LV] function parameters measured by gated myocardial perfusion SPECT [GSPECT] have been validated, experimental data have revealed that the calculated the LV function parameters using GSPECT are affected by patient populations as well as particular acquisition and processing conditions. We tried to determine the normal values of GSPECT in an Iranian population. We studied 3500 Iranian patients who underwent GSPECT in an outpatient setting. To develop normal limits of LV functional indices using GSPECT, 148 patients with a low [<5%] likelihood of coronary disease and normal tomograms were selected. No one of 148 patients had known coronary artery disease, typical angina, history of hypertension, diabetes mellitus, and smoking, any abnormality in echocardiography or hyperlipidemia. They were not taking any medication known to affect LV function at least 2 days before the study. End diastolic volume [EDV], end systolic volume [ESV] and LV ejection fraction [LVEF] were calculated in rest GSPECT using iterative reconstruction and QGS [quantitative gated SPECT] software. Mean EDV, ESV and LVEF were 53.8 +/- 20.2, 14.3 +/- 10.8 and 75.0% +/- 9.6% respectively. These data showed a Gaussian distribution, so mean_2SD would show the upper or lower limits of normal for LV functional parameters. There were the marked sex differences in mean LVVs and LVEF measurements. BMI index had not effect on the measurement of the LV functional parameters. We noticed that 85.4% of our subjects had ESV<25 ml while most of them were women [112/123, 91%]. From a clinical viewpoint, each institute should use a standard protocol for the specific patient population and for the mode of SPECT acquisition and reconstruction. Normal thresholds using GSPECT, OSEM reconstruction and QGS algorithm in men and women were EDV>130, ESV>55 and LVEF<52% and EDV>77, ESV> 26 and LVEF<62% respectively

Evaluation of the role of system matrix in SPECT images reconstructed by OSEM technique

Ordered subset expectation maximization [OSEM], is an effective iterative method for SPECT image reconstruction. The aim of this study is the evaluation of the role of system matrix in OSEM image reconstruction method using four different physical beam radiation models with three detection configurations. SPECT was done with an arc of 180 degree in 32 projections after injection of 2 mCi of [99m]Tc-pertechnetate in a heart phantom by a Siemens E.Cam gamma camera equipped with LEHR collimator and data were transferred to a PC computer for reconstruction of the images with Mathlab software. The system or probability matrixes were firstly calculated using radiation fraction of pixels for three different detection models with linear, rectangular and divergent FOV, and reduction coefficient of photons from pixels to detectors in four different radiation models of distance independent [DID], inverse distance dependence [IDD] [= 1/R], inverse square distance dependence [ISDD],[= 1/R[2]] and inverse exponential distance dependence[IEDD], [= exp-R]. In these calculations the detector was assumed at a distance of 842 mm from the phantom center and pixel size was 6.638 mm. The divergent angle in divergent field of view was 2.08 degree. 12 Images of the phantom were reconstructed using system matrixes of 4 different radiation and 3 detection models. Qualities of the images were compared using universal image quality index, UIQI. The results shows negligible although statistically significant difference between contrast and brightness of the images, but it is possible in the organs with constant absorption coefficients such as brain, to use the system matrix with mathematical IEDD radiation model for attenuation correction in SPECT images. It is shown that variation in distance weighting factors in mathematical IEDD radiation model changes the system matrix so that the weights of deeper data decrease in image reconstruction process. Therefore, by this method contrast of the image at different depth can be controlled. Applying different beam radiation models and detection configurations in system matrix has no significant improvements on the image quality. However image contrast at different depth can be controlled by using system matrix derived from different distance weighting factor in mathematical IEDD radiation model