Quantification of PET and CT misalignment errors due to bulk motion in cardiac PET/CT imaging: phantom and clinical studies

Non simultaneous acquisition between CT and PET module can introduce misalignment artefact in cardiac PET/CT imaging due to patient motion. We assessed the clinical impact of patient motion and the resulting mismatch between CT and corresponding CT-based attenuation corrected [CTAC] PET images on apparent myocardial uptake values in cardiac PET/CT imaging. The evaluation of patient motion was performed using clinical and experimental phantom studies acquired on the Biograph TP 64 PET/CT scanner. In order to simulate patient motion, CT images were manually shifted from 0 to 20 mm in steps of 5-mm in six different directions. The reconstructed PET images using shifted CT were compared with the original PET images. The assessment of PET images was performed through qualitative interpretation by an experienced nuclear medicine physician and through quantitative analysis using volume of interest based analysis. Moreover, Box and Whisker plots were calculated and bull's eye view analysis performed. PET images were also reoriented along the short, horizontal and vertical long axis views for a better qualitative interpretation. A 20-mm shift in the right direction between attenuation and PET emission scans produced mean absolute percentage difference in uptake values in the lateroanterior [33.42 +/- 9.07] and lateroinferior [27.39 +/- 10.43] segments of the myocardium. Misalignment could introduce artifactual nonuniformities in apparent myocardial uptake value and the variations were more significant for the misalignment toward the right, feet and head directions, in such a way that even with a 5-mm shift in the CT image, errors in interpretation of PET images could occur. Furthermore, errors in PET uptake estimates were observed for movements as large as 10-mm in the left, posterior and anterior directions

Experimental evaluation of the performance of HiReSPECT scanner: a high-resolution SPECT system for small animal imaging

In this report, the preliminary results of the experimental evaluation of the Performance of HiReSPECT scanner have been illustrated. In order to assess the capability of the scanner in both planar and tomographic modes, three rats were injected with 99mTc, 99mTc-DMSA, and 99mTc-MDP for thyroid scan, kidney scan and bone scan respectively in order to perform planar imaging. In addition, two rats were injected with 99mTc-MIBI and 99mTc-DMSA to perform cardiac and kidney tomographic imaging, respectively. Tomographic and planar scans of the rat organs showed that radioactive distribution in cardiac, kidney, bone and thyroid images exhibited detailed physiologic information of the imaged organs. Due to high resolution performance of the scanner, thyroid lobes are well depicted and distinguished from each other. Results of the evaluation of the planar and tomographic images indicated that HiReSPECT has appropriate imaging capability as an imaging system in biomedical research

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]

Computed tomography based attenuation correction in PET/CT: principles, instrumentation, protocols, artifacts and future trends

The advent of dual-modality PET/CT imaging has revolutionized the practice of clinical oncology, cardiology and neurology by improving lesions localization and the possibility of accurate quantitative analysis. In addition, the use of CT images for CT-based attenuation correction [CTAC] allows to decrease the overall scanning time and to create a noise-free attenuation map [micro map]. The near simultaneous data acquisition in a fixed combination of a PET and a CT scanner in a hybrid PET/CT imaging system with a common patent table minimizes spatial and temporal mismatches between the modalities by elimination the need to move the patient in between exams. As PET/CT technology becomes more widely available, studies are beginning to appear in the literature that document the use of PET/CT in a variety of different cancers, including lung, thyroid, ovarian, lymphoma, and unknown primary cancers, and for general oncology, cardiology and neurology applications. Specific applications of PET/CT, such as those for radiation therapy planning, are also being explored. The purpose of this review paper is to introduce the principles of PET/CT imaging systems and describe the sources of error and artifact in CT-based attenuation correction algorithm. This paper also focuses on recent developments and future trends in hybrid imaging and their areas of application. It should be noted that due to limited space, the references contained herein are for illustrative purposes and are not inclusive; no implication that those chosen are better than others not mentioned is intended