Introductions: Respiratory motion causes inaccurate PET and CT image co-registration especially in the thorax region and leads to non accurate ATTENUATION CORRECTION, understimation of lesion’s SUV and lesion volume overestimation, consequently leading to inaccurate PET data quantification. Different approaches have been developed to manage the respiratory motion problem, but the actual impact of respiratory motion ARTIFACT in routine clinical PET/CT imaging is not well characterized yet. The aim of this study is to quantify the impact of respiratory motion on CT-based ATTENUATION CORRECTION of PET data during oncological imaging of lung lesions.Methods: The 4D Extended Cardiac Torso (XCAT) software phantom was used to simulate respiratory motion cycle. Two sets of emission maps (activity distribution) and ATTENUATION maps (mmap) of the chest were generated: the first was generated in one of the phases in respiratory period, at the end-expiration phase, called motion-free, and the latter was the average of 8 phases of the respiratory cycle, called motion-blurred. lesions with defined activity were simulated in the lung. In order to generate emission sinograms of mentioned emission images STIR (Software for Tomographic Image Reconstruction) was used. emission sinograms were attenuated with corresponding ATTENUATION maps. Thereafter, ATTENUATION CORRECTION of static emission sinograms was done with the matched ATTENUATION maps. Also ATTENUATION CORRECTION of motionblurred emission data was performed with the motion-free ATTENUATION maps leading to mismatched PET/CT image registration. Poisson noise was also added to the sinograms to simulate almost real PET/CT data. PET images were reconstructed with OSEM algorithm followed by a 6 mm Gaussian filter using STIR code. The variations of lesion Standardized Uptake Values (SUVmax) between motion-free and motion-blurred PET/CT images were measured and analyzed.Results: For respiration with 16 mm diaphragm motion and 1 cm lesion mismatched ATTENUATION CORRECTION can cause lesion SUVmax underestimation of over 26% due to misaligned CT and PET images. For the lesions in the lower lung region, if the range of diaphragm motion varies from 6 to 16 mm, normalized error increases from 13% to 38% in motion-blurred images.Conclusion: Respiratory motion can have a significant impact on CT-based ATTENUATION CORRECTION of PET in lung imaging. In oncological PET/CT imaging where SUV and lesion volumes are important factors for evaluating response to therapy or radiotherapy planning, respiratory motion CORRECTION methods seems to be mandatory.

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.

Introduction: Photon ATTENUATION is one of the main causes of quantitative errors and ARTIFACTs in SPECT. CT based ATTENUATION map is necessary to correct for this effect accurately. A number of ATTENUATION related ARTIFACTs are described. A fast and memory efficient algorithm is proposed for ATTENUATION CORRECTION.Methods: In our CT based ATTENUATION CORRECTION algorithm, attenuated projections of an arbitrary estimation are calculated. These projections are compared with real projections. The error due to comparison updates the first arbitrary image. This iterative procedure continues till there is no difference between mathematical and real projections. To consider the effect of Poisson noise during reconstruction, EM statistical reconstruction is used. The effect of ATTENUATION is enrolled in both projection and backprojection steps. To accelerate the reconstruction algorithm, a rotating image in a fix grid with bilinear interpolation is used to simplify ray tracing for creating mathematical projections. OSEM with much faster convergence rate is also used instead of MLEM as iterative algorithm. Different phantom configurations with uniform and non-uniform ATTENUATION map are used to evaluate the accuracy of this algorithm. Projections free from the effect of ATTENUATION were also simulated. Reconstructed image from these ATTENUATION free projections is considered as reference image. Normalized mean square error between reference and corrected image and image contrast were used for quantitative evaluation of this algorithm.Results: contrast of central hot spot reduced to about half of its real contrast due to ATTENUATION. Non-uniformities, like hot skin, bright long related spots and colds bone related spots were also created in non-corrected images due to ATTENUATION. All ATTENUATION related ARTIFACTs removed after ATTENUATION CORRECTION. NMSE is reduced from 1 in non-corrected images to 0.1 in corrected images. Much better fit in line profile of corrected images and reference images were also observed.Conclusion: By using more suitable models for image formation it is possible to reconstruct images with much higher quantitative and qualitative accuracy which is essential in both diagnostic and image guided therapy procedures.

Introduction: ATTENUATION CORRECTION is a useful process for improving myocardial perfusion SPECT and is dependent on activity and distribution of ATTENUATION coefficients in the body (ATTENUATION map). ATTENUATION ARTIFACTs are a common problem in myocardial perfusion SPECT. The aim of this study was to compare the effect of ATTENUATION CORRECTION using different ATTENUATION maps and different activities in a specially designed heart phantom.Methods: The SPECT imaging for different activities and different body contours were performed by a phantom using tissue-equivalent boluses for making different thicknesses. The activity was ranged from 0.3-2mCi and the images were acquired in 180 degree, 32 steps. The images were reconstructed by OSEM method in a PC computer using Matlab software. ATTENUATION map were derived from CT images of the phantom. Two quality and quantity indices, derived from universal image quality index have been used to investigate the effect of ATTENUATION CORRECTION in each SPECT image.Results: The result of our measurements showed that the quantity index of corrected image was in the range of 3.5 to 5.2 for minimum and maximum tissue thickness and was independent of activity. Comparing ATTENUATION corrected and uncorrected images, the quality index of corrected image improved by increasing body thickness and decreasing activity of the voxels.Conclusion: ATTENUATION CORRECTION was more effective for images with low activity or phantoms with more thickness. In our study, the location of the pixel relative to the associated attenuator tissues was another important factor in ATTENUATION CORRECTION. The more accurate the registration process (ATTENUATION map and SPECT) the better the result of ATTENUATION CORRECTION.

Background: Photon ATTENUATION as an inevitable physical phenomenon influences on the diagnostic information of SPECT images and results to errors in accuracy of quantitative measurements. This can be corrected via different physical or mathematical approaches. As the CORRECTION equation in mathematical approaches is nonlinear, in this study a new method of linearization called ‘Piece Wise Linearization’ (PWL) is introduced and to substantiate its validity for SPECT image reconstructions, a phantom study is performed. Material and Methods: A SPECT scan of a homemade heart phantom filled with 2 mCi 99mTc was acquired by dual head Siemens E.Cam gamma camera equipped with LEHR collimator. Row data of the scan were transferred in DICOM format to a pc computer for reconstruction of the images using MLEM iterative algorithm in Matlab software. Result: ATTENUATION map of the phantom m(x) were derived using PWL with linear optimization approach. Based on that, the ATTENUATION corrected SPECT image of the phantom were reconstructed and compared with non-corrected image, using MLEM iterative algorithm. Comparison of the corrected and non-corrected images confirmed with CT ATTENUATION CORRECTION method. Conclusion: ATTENUATION CORRECTION in SPECT image can be achieved successfully, using emission data and piecewise linearization with linear optimization approach. The corrected image of ¦(x) and ATTENUATION map m(x) of the heart phantom using this approach promise acceptable image quality for diagnostic clinical use.

Introduction: The advent of dual-modality PET/CT scanners has revolutionized clinical oncology by improving lesion localization and facilitating treatment planning for radiotherapy. In addition, the use of CT images for CT-based ATTENUATION CORRECTION (CTAC) decreases the overall scanning time and creates a noise-free ATTENUATION map (mmap). CTAC methods include scaling, segmentation, hybrid scaling/segmentation, bilinear and dual energy methods. All CTAC methods require the transformation of CT Hounsfield units (HU) to linear ATTENUATION coefficients (LAC) at 511 keV. The aim of this study is to compare the results of implementing different methods of energy mapping in PET/CT scanners.Materials and Methods: This study was conducted in 2 phases, the first phase in a phantom and the second one on patient data. To perform the first phase, a cylindrical phantom with different concentrations of K2HPO4 inserts was CT scanned and energy mapping methods were implemented on it. For performing the second phase, different energy mapping methods were implemented on several clinical studies and compared to the transmission (TX) image derived using Ga-68 radionuclide source acquired on the GE Discovery LS PET/CT scanner.Results: An ROI analysis was performed on different positions of the resultant µmaps and the average mvalue of each ROI was compared to the reference value. The results of the µmaps obtained for 511 keV compared to the theoretical values showed that in the phantom for low concentrations of K2HPO4 all these methods produce 511 keV ATTENUATION maps with small relative difference compared to gold standard. The relative difference for scaling, segmentation, hybrid, bilinear and dual energy methods was 4.92, 3.21, 4.43, 2.24 and 2.29%, respectively. Although for high concentration of K2HPO4 the three methods; hybrid scaling/segmentation, bilinear and dual energy produced the lowest relative difference of 10.91, 10.88 and 5%, respectively. For patients it was found that for soft tissues all the mentioned energy mapping methods produce acceptable ATTENUATION map at 511 keV. The relative difference of scaling, segmentation, hybrid, and bilinear methods compared to TX method was 6.95, 4.51, 7, and 6.45% respectively. For bony tissues, the quantitative analysis showed that scaling and segmentation method produce high relative difference of 26 and 23.2%, respectively and the relative difference of hybrid and bilinear in comparison to TX method was 10.7 and 20%, respectively.Discussion and Conclusion: Based on the result obtained from these two studies it can be concluded that for soft tissues all energy mapping methods yield acceptable results while for bony tissues all the mentioned methods except the scaling and segmentation yield acceptable results.

Purpose: At Magnetic Resonance Imaging (MRI), ARTIFACTs arising from metal implants are an obstacle to obtaining optimal images. This study aimed to evaluate the impact of View-Angle Tilting (VAT) and Slice Encoding for Metal ARTIFACT CORRECTION (SEMAC) techniques for the ARTIFACT reduction of patients during knee MRI with metal implants. Materials and Methods: The MR images without any intervention of the knee from 20 patients with knee prostheses were used. The VAT and SEMAC metal ARTIFACT reduction techniques were applied to all the MR images. Volume and mass of the metal prosthesis were quantified using the MATLAB program and compared with the real measurements using nonparametric Wilcoxon tests in SPSS software. The qualitative analysis was performed by two blinded observers regarding the score of ARTIFACT size, distortions, image quality, and visualization of bone marrow and soft tissues adjacent to metal implants. In addition, Cohen’, s kappa values were used for inter-observer agreement. Results: The average volume of the platinum based on the conventional, VAT, and SEMAC methods was estimated at 14. 22 ±,0. 43, 14. 05 ±,0. 4, and 13. 3 ±,0. 45 cm3, respectively. The statistical analysis showed no significant difference (P > 0. 05) between the mean value of the platinum volume for the SEMAC method and the real measurement (13. 6 ±,0. 33 cm3). Furthermore, regarding the conventional, VAT, and SEMAC sequences, the mean mass of the platinum was obtained at 305. 02 ±,9. 22, 301. 37 ±,8. 58, and 285. 28 ±,9. 65 g, respectively, with the P-Value of 0. 005, 0. 009, and 0. 268, compared to the real measurements (286. 81±, 8. 75 g). Notably, the blinded readers demonstrated that the SEMAC method was remarkably superior quality compared with VAT and conventional acquisitions (P-Value< 0. 05). Conclusion: The knee prosthesis metal ARTIFACT was reduced using the VAT and SEMAC techniques, in a way that, the reduction was significant by the SEMAC method. In addition, concerning the qualitative observer analysis, the application of the SEMAC technique provides improved visualization of tissue structures adjacent to metal implants.

Introduction: Nowadays, Imaging of the myocardial perfusion (MPI) using the single photon emission tomography (SPET) in the diagnosis of coronary artery disease, especially myocardial ischemia, is of great importance. In contrast to the coronary artery angiography, MPI is non-invasive, less expensive and more physiological. Unfortunately, this image is affected by the some ARTIFACTs. These ARTIFACTs lead to decrease image diagnostic accuracy and increase false positive cases. One of the most important effective ARTIFACTs is due to ATTENUATION. These ATTENUATION ARTIFACTs are caused by the left breast tissue in women, diaphragm in men and the chest wall in both sexes. Because of the inherent non- uniform ATTENUATION map in the thorax region, this problem is very complex. Methods: The aim of this study is to correct ATTENUATION ARTIFACT with a simple method that is available and very easy to use. In this study we used transmission scanning by 99mTc in the sequential views and an ATTENUATION map was created.After ATTENUATION CORRECTION of the original images with ATTENUATION map, non corrected and corrected images were compared with angiography results to apply ATTENUATION CORRECTION based on functional findings. Results: Results show that new ARTIFACTs are created and experiences of physicians in the impression of the images is critical. Finally, the sensitivity of images increased from 86.20% to 96.42%, the specificity decreased from 85.71% to 54.54% and the diagnostic accuracy decreased from 86% to 78%. Conclusion: ATTENUATION CORRECTION can produce new ARTIFACTs, which can influence the way scans are interpreted. It seems that ATTENUATION CORRECTION of the images, need special experience. Lack of enough experience in ATTENUATION CORRECTION techniques, can comprise the diagnostic accuracy of images.

In modern PET/CT systems, the CT provides a fast and relatively noise-free ATTENUATION map and improving lesions localization and the possibility of accurate quantitative analysis. In cardiac imaging, there is a strong ATTENUATION gradient along the myocardial free wall, with muscle next to the air of the lung space and heart has movement and located in the place that move due to breathing cause misalignment increases in this area. If misalignments occur along these boundaries, the ATTENUATION CORRECTION factors are potentially inaccurate, causing as much as a 60% error in the PET tracer emission image in the critical regions of diagnostic interest. ARTIFACTs caused by misalignment are particularly disconcerting in cardiac imaging because they can present themselves as perfusion abnormalities or erroneous information on myocardial viability. In This paper the accuracy of some CT protocols such as gated, normal (a high-pitch helical CT), slow ct, low-temporalresolution helical CT, time-averaged CT (ACT), ultra low dose CT that normally used for ATTENUATIONCORRECTION in PET/CT were compared, moreover the image quality and dose that induced to patient from each protocols. Acquiring a slow CT improved registration between the transmission and emission. Potential for a heightened radiation dose delivered by the slow CT was compensated by doubling the default noise index and increasing the slice thickness to 5 mm. In the low-dose average cine CT, Further reduction in dose is possible by lowering the upper threshold of the auto-mA settings or modulation of the CT tube current based on anatomy. ACT protocols consist of multiple images acquired sequentially (also referred to as cine or axial) along the bed length over the span of one or more respiratory cycles. 2% average increase in ACT-PET rest reconstruction values compared the HCT-PET rest reconstruction values was slightly higher than the bias calculated. Contrary to the HCT protocol, the ACT protocol provides more flexibility in addressing ARTIFACTs such as varying the respiratory phases used to create the time-averaged CT to suppress respiratory ARTIFACTs. In addition, photon starvation can be addressed by optimizing the acquisition parameters, such as increasing the tube voltage and current in patients with high BMI values. Ultra-low-dose CT’s shorter duration and the lower radiation and revealed no severe shift of the myocardium between the CT-based transmission and the emission in the patients.

Introduction: Integration of single photon emission computed tomography (SPECT) and computed tomography (CT) scanners into SPECT/CT hybrid systems permit detection of coronary artery disease in myocardial perfusion imaging (MPI). Misregistration between CT and emission data can produce some errors in uptake value of SPECT images. The aim of this study was evaluate the influence of ATTENUATION CORRECTION (AC) versus non-ATTENUATION CORRECTION (NC) images and the effect of misregistration on all segments of SPECT images for quantitative and qualitative analysis. Methods: 99 patients (45 males, 54 females) underwent stress/rest myocardial perfusion imaging (MPI) using 99mTc-MIBI were used in this study. We also utilized cardiac insert and lung insert in cylinder phantom. Phantom studies were performed with and without defect. The misregistration of all patient data was measured and variation in misregistration of our population was recorded. The effect of ATTENUATION CORRECTION (AC) and non-ATTENUATION CORRECTION (NC) images were also evaluated in both phantom and patient data. The CT images were shifted by ± 1, ± 2, ± 3 pixels along X-, Y-and Z-axis (Left/right, dorsal/ventral, cephalic/caudal) for both phantom and patient studies. Differences between misalignment data and misregistration CORRECTION images were also measured. Results displayed with 20 segments polar map analysis and illustration in standard orientations for cardiac tomographic images. Results: In the patient population data, 1. 5% were perfectly registered, 17% and 73% misaligned under 1 pixel and more than 1 pixel, respectively. AC of SPECT images showed increased uptake value in normal phantom and false positives findings were disappeared versus to NC images. In patient data, statistically significant variation were shown for the most segments before and after AC (P-value<=0. 004) and also between AC of SPECT image and misregistration CORRECTION images (P-value<=0. 048). Along X-axis, in 3 pixel shift in right direction, the percent of relative difference in lateral wall were 11. 94% for mid anterolateral. Along Y-axis, the Ventral shift caused-15. 9% changes in basal inferolateral and along Z-axis-8. 59 % changes in apical anterolateral were also observed in caudal direction when 3 pixel shifts were used. Conclusion: This study showed that CT-based ATTENUATION CORRECTION of cardiac images in hybrid SPECT/CT is important to improve image quality. Misalignment in caudal, cephalad, ventral and right direction introduced significant variation even in 1 pixel shift. It is important to apply misregistration CORRECTION even in small misalignment routinely in clinical myocardial perfusion imaging.