comparative assessment of dynamic and conventional thallium-201 SPECT myocardial perfusion imaging: monte carlo simulations and case studies

Purpose: Clinical myocardial perfusion SPECT is commonly performed using static imaging. Dynamic SPECT enables extraction of quantitative as well as relative perfusion information. We aimed to evaluate the ability of dynamic SPECT for regular perfusion assessment in comparison to conventional SPECT in the context of thallium-201. Methods: Simulations were performed utilizing a 4D-NCAT phantom for a dual-head gamma camera via the SIMIND Monte-Carlo simulator. 64s acquisition time-frames were used to track these dynamic changes. Different summations of time-frames were performed to create each dataset, which were compared to a standard static dataset. In addition, the effect of different delay-times post-injection was assessed. Twenty-segment analysis of perfusion was performed via the QPS analyser. Dynamic data were subsequently acquired in clinical studiesusing simulation-optimized protocols. Results: For different summations of time-frames, perfusion scores in the basal and mid regions revealed 14.4% and 7.3% increases in dynamic SPECT compared to conventional imaging, with maximum changes in the basal anterior, while the distal and apical segments did not show noticeable changes. Specifically, dynamic imaging including 4 to 6 time-frames yielded enhanced correlation [R=0.957] with conventional imaging, in comparision to the usage of less time frames. Greatest correlation with conventional imaging was obtained for post-injection delays of 320 to 448s [R=0.982 to R=0.988]. Conclusion: While dynamic SPECT opens up an important opportunity for quantitative assessment [e.g. via generation of kinetic parameters], it was shown to generate highly consistent perfusion information compared to established conventional imaging. Future work focuses on merging these two important capabilities

Assessment of the imact of applying attenuation correction on the accuracy of activity recovery in Tc99m-ECD brain SPECT of healthy subject using statistical parameters mapping [SPM]

Photon attenuation in tissues is the primary physical degrading factor limiting both visual qualitative interpretation and quantitative analysis capabilities of reconstructed Single Photon Emission Computed Tomography [SPECT] images. The aim or present study was to investigate the effect of attenuation correction on the detection of activation foci following statistical analysis was SPM. The study population consisted of twenty normal subjects [11 male, 9 female, and age 30-40 years]. SPECT images were reconstructed using filter back projection and attenuation correction was done by the Chang method. The SPECT imagings was obtained 20 min after intravenous injection of 740-1110 MBq [20-30 mCi] of Tc99m-ECD and were acquired on 128x128 matrices with a 20% symmetric energy window at 140 keV. These data publicly distributed by the Society of Nuclear Medicine of Toronto Hospital. the data was standardized with respect to the Montreal Neurological institute [MNI] atlas with a 12 parameter affine transformations. Images were then smoothed by a Gaussian filter of 10 mm FWHM. Significance differences between SPECT images were estimated at every voxel using statistical t-test and p-value as the significant criteria was set at 0.05. The contrast comparing non attenuation corrected images suggest that regional brain perfusion activity increase in the cerebrum, frontal [T-value 12.06], temporal [T-value 10.63] and occipital [T-value 9.31] lobe and decrease in the sub-lobar, extra-nuclear [T-value 17.46] and limbic lobe, posterior cingulated [T-value 17.46] before attenuation correction compare with attenuation correction. It can be concluded that applying correction in brain SPECT can effectively improve the accuracy of the detection of activation are [p<0.05]

[Design, simulation and manufacture of a multileaf collimator to confirm the target volumes in intensity modulated radiation therapy]

Intensity modulated radiation therapy [IMRT] is one of the cancer treatment methods. It is important to selectively aim at the target in this way, which can be performed using a multileaf collimator [MLC]. In order to specifically irradiate the target volume in radiotherapy to reduce the patient absorbed dose, the use of multileaf collimator has been investigated in this work. Design and simulation of an MLC was performed by a Monte Carlo method and the optimum material for manufacturing the leaves was determined using MCNP4C. After image processing [CT or MRI] in this system, the tumor configuration is determined. Then the linear accelerator is switched on and the beam irradiates the cancerous cells. When the MLC leaves receive a command from the mircrocontroller, they start to move and absorb the radiation and modulate its intensity. Consequently, the tumor receives maximum intensity of radiation but minimum intensity is delivered to healthy tissues. According to the simulations and calculations, the best material to manufacture the leaves from is tungsten alloy containing copper and nickel which absorbs a large amount of the radiation; by using a 8.65 cm thickness of alloy, 10.55% of radiation will transmit through the leaves. Lead blocks are conventionally used in radiotherapy. However, they have some problems like cost, storage and manufacture for every patient. Certainly, the MLC is the most efficient device to specifically irradiate the tumor in IMRT. Furthermore, it facilitates treating the target in different views by rotation around the patient. Thus the patient's absorbed dose will decrease and the tumor will receive maximum dose

[Detection of cardiac artery disease by using the DCAD [b] module]

In patients with cardiac artery disease, a myocardial perfusion scan, which is a noninvasive method, is utilized. This study is conducted to develop an advantageous s o h e applicable to quantitative myocardial SPECT perfusion. Each cross-section of the left ventricle was segmented by applying a fuzzy clustering method. After obtaining the myocardial skeleton of the left ventricle from its short axis cross sections, we made use of fuzzy logic to decide whether the pixel belongs to the myocardial muscle and any perfusion perturbation or not. The reconstructed image was divided into 18 equivoque sectors. The features were extracted in each sector and, finally, were compared with a normal data bank. Abnormal critical conditions in rest and stress studies and coronary artery disease diagnosis were investigated in a set of about 317 images. Measurement and allocation of different myocardial sectors to specific coronary arteries were accomplished by utilizing collected information about the patients [75 men and 62 women], and the validity of the artery obstruction diagnosis has been proven in 40 patients undergoing coronary angiography. Our developed software DCAD [b] has demonstrated a considerably good performance in the diagnosis of coronary artery occlusion and can be promising method aiding nuclear medicine specialists in their diagnosis