Attenuation Correction In Single Photon Emission Computed Tomography Research Articles

DuDoCFNet: Dual-Domain Coarse-to-Fine Progressive Network for Simultaneous Denoising, Limited-View Reconstruction, and Attenuation Correction of Cardiac SPECT.

Single-Photon Emission Computed Tomography (SPECT) is widely applied for the diagnosis of coronary artery diseases. Low-dose (LD) SPECT aims to minimize radiation exposure but leads to increased image noise. Limited-view (LV) SPECT, such as the latest GE MyoSPECT ES system, enables accelerated scanning and reduces hardware expenses but degrades reconstruction accuracy. Additionally, Computed Tomography (CT) is commonly used to derive attenuation maps (μ-maps) for attenuation correction (AC) of cardiac SPECT, but it will introduce additional radiation exposure and SPECT-CT misalignments. Although various methods have been developed to solely focus on LD denoising, LV reconstruction, or CT-free AC in SPECT, the solution for simultaneously addressing these tasks remains challenging and under-explored. Furthermore, it is essential to explore the potential of fusing cross-domain and cross-modality information across these interrelated tasks to further enhance the accuracy of each task. Thus, we propose a Dual-Domain Coarse-to-Fine Progressive Network (DuDoCFNet), a multi-task learning method for simultaneous LD denoising, LV reconstruction, and CT-free μ-map generation of cardiac SPECT. Paired dual-domain networks in DuDoCFNet are cascaded using a multi-layer fusion mechanism for cross-domain and cross-modality feature fusion. Two-stage progressive learning strategies are applied in both projection and image domains to achieve coarse-to-fine estimations of SPECT projections and CT-derived μ-maps. Our experiments demonstrate DuDoCFNet's superior accuracy in estimating projections, generating μ-maps, and AC reconstructions compared to existing single- or multi-task learning methods, under various iterations and LD levels. The source code of this work is available at https://github.com/XiongchaoChen/DuDoCFNet-MultiTask.

Attenuation and scatter correction in I-123 FP-CIT SPECT do not affect the clinical diagnosis of dopaminergic system neurodegeneration.

The purpose of this study was to assess the influence of different reconstruction factors in N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-I-123 iodophenyl)nortropane (I-123 FP-CIT) single-photon emission computed tomography (SPECT) images for the diagnosis of dopaminergic system neurodegeneration (DSND).Seventy-three patients (38 females, 35 males) suspected of DSND were included in this study. The patients were divided into 3 groups on the basis of their final clinical diagnoses; patients with Parkinson disease (group 1, n = 36), patients with other DSND (group 2, n = 19), patients without DSND (group 3, n = 18). FP-CIT accumulation in the striata was evaluated visually and semiquantitatively. SPECT images were classified visually as normal or abnormal based on the previous report. For semiquantitative analysis, we used DaTView software (Aze Corporation), and specific binding ratios (SBR) and asymmetry indices (AI) were calculated. Visual and semiquantitative evaluations for different reconstruction factors were compared among the 3 groups.In the visual evaluation, there were no differences among DSND diagnostic capabilities of attenuation and scatter correction by computed tomography attenuation correction scatter correction, computed tomography attenuation correction, Chang attenuation correction, and non-attenuation and -scatter correction. In the semiquantitative evaluation, receiver operating characteristic analysis of SBR and AI for clinical DSND diagnostic ability (group 1+2 vs 3) showed no significant difference among the reconstruction factors by multiple comparisons.Although the values of SBR and AI were changed and image quality could be improved when attenuation correction and/or scatter correction were applied, the clinical impact of these reconstruction factors for the diagnosis of DSND was negligible.

Automatic cumulative sums contour detection of FBP-reconstructed multi-object nuclear medicine images

The problem of determining the contours of objects in nuclear medicine images has been studied extensively in the past, however most of the analysis has focused on a single object as opposed to multiple objects. The aim of this work is to develop an automated method for determining the contour of multiple objects in positron emission tomography (PET) and single photon emission computed tomography (SPECT) filtered backprojection (FBP) reconstructed images. These contours can be used for computing body edges for attenuation correction in PET and SPECT, as well as for eliminating streak artifacts outside the objects, which could be useful in compressive sensing reconstruction. Contour detection has been accomplished by applying a modified cumulative sums (CUSUM) scheme in the sinogram. Our approach automatically detects all objects in the image, without requiring a priori knowledge of the number of distinct objects in the reconstructed image. This method has been tested in simulated phantoms, such as an image-quality (IQ) phantom and two digital multi-object phantoms, as well as a real NEMA phantom and a clinical thoracic study. For this purpose, a GE Discovery PET scanner was employed. The detected contours achieved root mean square accuracy of 1.14 pixels, 1.69 pixels and 3.28 pixels and a Hausdorff distance of 3.13, 3.12 and 4.50 pixels, for the simulated image-quality phantom PET study, the real NEMA phantom and the clinical thoracic study, respectively. These results correspond to a significant improvement over recent results obtained in similar studies. Furthermore, we obtained an optimal sub-pattern assignment (OSPA) localization error of 0.94 and 1.48, for the two-objects and three-objects simulated phantoms, respectively. Our method performs efficiently for sets of convex objects and hence it provides a robust tool for automatic contour determination with precise results.

Improvements in Segmentation Using Scatter and Photopeak Window Data for Attenuation Correction in Myocardial SPECT

Background: The method of Segmentation with Scatter and Photopeak window data in Attenuation Correction (SSPAC) recognizes the outlines of the body around chest and lungs using scatter window data after which an attenuation correction (μ) map can be constructed.We have developed a new extraction method, adding a masking process to SSPAC, because the extraction of outlines was otherwise incomplete. Methods and Results: The masking process extracted right and left lung fields from chest images.The quality of the masking process was confirmed by the results from a low count phantom.In a case study, automatic extraction by SSPAC had a 44% success rate for low count (stress condition) myocardial single-photon emission computed tomography (SPECT) images, but reached a success rate of 99% with the addition of the new masking process.Outline truncation and low counts can cause unsuccessful SSPAC. Conclusions: Our method for masking will contribute to a widespread use of SSPAC by improving the success rate in contouring.

Investigation of attenuation correction in SPECT using textural features, Monte Carlo simulations, and computational anthropomorphic models.

To present and evaluate a new methodology to investigate the effect of attenuation correction (AC) in single-photon emission computed tomography (SPECT) using textural features analysis, Monte Carlo techniques, and a computational anthropomorphic model. The GATE Monte Carlo toolkit was used to simulate SPECT experiments using the XCAT computational anthropomorphic model, filled with a realistic biodistribution of (99m)Tc-N-DBODC. The simulated gamma camera was the Siemens ECAM Dual-Head, equipped with a parallel hole lead collimator, with an image resolution of 3.54 × 3.54 mm(2). Thirty-six equispaced camera positions, spanning a full 360° arc, were simulated. Projections were calculated after applying a ± 20% energy window or after eliminating all scattered photons. The activity of the radioisotope was reconstructed using the MLEM algorithm. Photon attenuation was accounted for by calculating the radiological pathlength in a perpendicular line from the center of each voxel to the gamma camera. Twenty-two textural features were calculated on each slice, with and without AC, using 16 and 64 gray levels. A mask was used to identify only those pixels that belonged to each organ. Twelve of the 22 features showed almost no dependence on AC, irrespective of the organ involved. In both the heart and the liver, the mean and SD were the features most affected by AC. In the liver, six features were affected by AC only on some slices. Depending on the slice, skewness decreased by 22-34% with AC, kurtosis by 35-50%, long-run emphasis mean by 71-91%, and long-run emphasis range by 62-95%. In contrast, gray-level non-uniformity mean increased by 78-218% compared with the value without AC and run percentage mean by 51-159%. These results were not affected by the number of gray levels (16 vs. 64) or the data used for reconstruction: with the energy window or without scattered photons. The mean and SD were the main features affected by AC. In the heart, no other feature was affected. In the liver, other features were affected, but the effect was slice dependent. The number of gray levels did not affect the results.

Robust, fully automatic delineation of the head contour by stereotactical normalization for attenuation correction according to Chang in dopamine transporter scintigraphy.

Chang's method, the most widely used attenuation correction (AC) in brain single-photon emission computed tomography (SPECT), requires delineation of the outer contour of the head. Manual and automatic threshold-based methods are prone to errors due to variability of tracer uptake in the scalp. The present study proposes a new method for fully automated delineation of the head based on stereotactical normalization. The method was validated for SPECT with I-123-ioflupane. The new method was compared to threshold-based delineation in 62 unselected patients who had received I-123-ioflupane SPECT at one of 3 centres. The impact on diagnostic power was tested for semi-quantitative analysis and visual reading of the SPECT images (six independent readers). The two delineation methods produced highly consistent semi-quantitative results. This was confirmed by receiver operating characteristic analyses in which the putamen specific-to-background ratio achieved highest area under the curve with negligible effect of the delineation method: 0.935 versus 0.938 for stereotactical normalization and threshold-based delineation, respectively. Visual interpretation of DVR images was also not affected by the delineation method. Delineation of the head contour by stereotactical normalization appears useful for Chang AC in I-123-ioflupane SPECT. It is robust and does not require user interaction. •Chang attenuation correction in brain SPECT requires delineation of the head contour. •Manual and threshold-based methods are prone to errors. •The study proposes a fully-automated method for delineation based on stereotactical normalization. •The method is shown to work reliably in I-123-ioflupane SPECT. •It might improve the workflow of I-123-ioflupane SPECT in everyday patient care.

A comparison of MR-based attenuation correction in PET versus SPECT

Attenuation correction (AC) is a critical step in the reconstruction of quantitatively accurate positron emission tomography (PET) and single photon emission computed tomography (SPECT) images. Several groups have proposed magnetic resonance (MR)-based AC algorithms for application in hybrid PET/MR systems. However, none of these approaches have been tested on SPECT data. Since SPECT/MR systems are under active development, it is important to ascertain whether MR-based AC algorithms validated for PET can be applied to SPECT. To investigate this issue, two imaging experiments were performed: one with an anthropomorphic chest phantom and one with two groups of canines. Both groups of canines were imaged from neck to abdomen, one with PET/CT and MR (n = 4) and the other with SPECT/CT and MR (n = 4), while the phantom was imaged with all modalities. The quality of the nuclear medicine reconstructions using MR-based attenuation maps was compared between PET and SPECT on global and local scales. In addition, the sensitivity of these reconstructions to variations in the attenuation map was ascertained. On both scales, it was found that the SPECT reconstructions were of higher fidelity than the PET reconstructions. Further, they were less sensitive to changes to the MR-based attenuation map. Thus, MR-based AC algorithms that have been designed for PET/MR can be expected to demonstrate improved performance when used for SPECT/MR.

Clinical and prognostic value of X-ray based attenuation correction in post-stress myocardial perfusion SPECT

Objective The purpose of the study was to validate the X-ray-based attenuation correction technique applied to post-stress myocardial perfusion single photon emission computed tomography (SPECT). Materials and methods Fifty-six patients with clinically suspected ischemic heart disease and no history of myocardial infarction or coronary revascularization were studied. All patients underwent a myocardial perfusion SPECT after exercise (38) or pharmacological stress (18). Mean clinical follow-up time was 18.6 months. Studies were assessed after reconstruction using the filtered back projection technique and after application of the X-ray-based attenuation correction technique, and the results obtained were related to the final clinical diagnosis. Results Eleven uncorrected studies were normal, while 45 studies showed perfusion defects. After attenuation correction, absence of significant perfusion defects was observed in 24 cases (42.9 % of all cases), and ischemic heart disease was finally ruled out in 22 cases. A greater study normalization rate was seen in men (p =0.048; odds ratio =2,923), but this fact was not shown to be significantly correlated to the following variables: pre-test probability of ischemic heart disease, body mass index greater than 30, presence of cardiovascular risk factors or otherwise, and age. Conclusions Application of the X-ray-based attenuation correction technique would have allowed for obviating the conduct of a resting perfusion study in 42.9 % of patients without apparently changing the diagnostic safety of the test. This fact was seen more frequently in men. This method seems to be both safe and time- and cost-effective.

Implementation of a Tc-99m and Ce-139 scanning line source for attenuation correction in SPECT using a dual opposing detector scintillation camera.

Image degradation during single photon emission computed tomography (SPECT) due to attenuation and Compton scatter of photons can cause clinical image artifacts and will also result in inaccurate quantitative data. Therefore attenuation correction methods recently received wide interest. Transmission imaging can be performed to obtain the attenuation coefficients of a nonhomogeneous attenuating medium accurately. The aim of this study was firstly to evaluate the imaging characteristics of the scanning line source assembly. The results obtained with Tc-99m and Ce-139 were compared. Secondly the calculated attenuation coefficients were compared with known values from literature, using Tc-99m and Ce-139 as transmission sources. Lastly the method of acquiring simultaneous transmission and emission data was investigated. This study shows that an attenuation coefficient map can be obtained using a scanning line source for transmission imaging with a dual opposing detector camera. The imaging characteristics of Tc-99m and Ce-139 as transmission sources are similar. The resolution obtained with the Ce-139 line source was poorer than that obtained with the Tc-99m line source. A linear relationship was found between CT numbers and attenuation coefficients for transmission images using both Tc-99m and Ce-139 line sources. The attenuation coefficient value for water was underestimated by 1% using the Tc-99m transmission source and underestimated by 10% using Ce-139 as transmission source. This underestimation of attenuation coefficient values was also obtained in the human study. A myocardial perfusion study processed without and with attenuation correction clearly demonstrated the effect of the attenuation correction in the inferior myocardial region. The potential of using a scanning line source as transmission source with a dual opposing detector camera has been demonstrated in this study. The transmission source, Ce-139 was successfully introduced in this investigation for simultaneous acquisition of transmission and emission data.

Evaluation of attenuation corrections using Monte Carlo simulated lung SPECT

SPECT (single photon emission computed tomography) images are distorted by photon attenuation. The effect is complex in the thoracic region due to different tissue densities. This study compares the effect on the image homogeneity of two different methods of attenuation correction in lung SPECT; one pre-processing and one post-processing method. This study also investigates the impact of attenuation correction parameters such as lung contour, body contour, density of the lung tissue and effective attenuation coefficient. The Monte Carlo technique was used to simulate SPECT studies of a digital thorax phantom containing a homogeneous activity distribution in the lung. Homogeneity in reconstructed images was calculated as the coefficient of variation (CV). The isolated effect of the attenuation correction was assessed by normalizing pixel values from the attenuation corrected lung by pixel values from the lung with no attenuation effects. Results show that the CV decreased from 12.8% with no attenuation correction to 4.4% using the post-processing method and true densities in the thoracic region. The impact of variations in the definition of the body contour was found to be marginal while the corresponding effect of variations in the lung contour was substantial.

Toward accurate attenuation correction in SPECT without transmission measurements.

The current trend in attenuation correction for single photon emission computed tomography (SPECT) is to measure and reconstruct the attenuation coefficient map using a transmission scan, performed either sequentially or simultaneously with the emission scan. This approach requires dedicated hardware and increases the cost (and in some cases the scanning time) required to produce a clinical SPECT image. Furthermore, if short focal-length fan-beam collimators are used for transmission imaging, the projection data may be truncated, leading to errors in the attenuation coefficient map. Our goal is to obtain information about the attenuation distribution from only the measured emission data by exploiting the fact that only certain attenuation distributions are consistent with a given emission dataset. Ultimately this consistency information will either be used directly to compensate for attenuation or combined with the incomplete information from fan-beam transmission measurements to produce a more accurate attenuation coefficient map. In this manuscript the consistency conditions (which relate the measured SPECT data to the sinogram of the attenuation distribution) are used to find the uniform elliptical attenuation object which is most consistent with the measured emission data. This object is then used for attenuation correction during the reconstruction of the emission data. The method is tested using both simulated and experimentally acquired data from uniformly and nonuniformly attenuating objects. The results show that, for uniform elliptical attenuators, the consistency conditions of the SPECT data can be used to produce an accurate estimate of the attenuation map without performing any transmission measurements. The results also show that, in certain circumstances, the consistency conditions can prove useful for attenuation compensation with nonuniform attenuators.

State of the art in emission tomography equipment.

The current state of the art in single photon emission computed tomography (SPECT) and positron emission tomography (PET) equipment is based on developments over the last 35 years, including those items necessary to make the devices clinically useful. In SPECT, most of the development has involved rotating gamma cameras, since this device could also be used for conventional planar imaging. Recent advances involve the use of multiheaded SPECT cameras and have led to a substantial increase in image quality with these devices. Historically, attenuation correction in SPECT has been applied only to brain and abdominal studies. Currently, the application of nonuniform attenuation correction for cardiac studies, which typically requires acquisition of a transmission scan, has been investigated. Over the past 10 years, greater interest in the clinical application of PET has led to design changes in the equipment used for chemistry and scanning. Modern cyclotrons are typically smaller, self-shielded, and less complicated to run than older models. PET scanners can now image multiple planes over an extended axial field of view with approximately equal spatial resolution in all directions. Advancements in emission tomography have made these technologies more accessible for clinical application.

Attenuation correction in cardiac positron emission tomography and single-photon emission computed tomography.

Quantitation in cardiac positron emission tomography (PET) and single-photon emission computed tomography (SPECT) depends on being able to correct for several physical factors that tend to distort the data. One of the most important of these corrections is the correction for attenuation. For PET, cardiac attenuation correction is a reality, although certain problems remain to be solved. For SPECT, recent developments in gamma camera hardware and reconstruction methods have finally made it possible to attempt attenuation correction in a clinical setting. This article reviews the methods available to perform attenuation correction in both PET and SPECT, with emphasis on the commonality between the problems encountered and solutions proposed for each modality.

Non-uniform attenuation and scatter correction in SPECT

Using a large test object containing an asymmetrical distribution of Tc-99m activity and having nonuniform attenuation, techniques have been developed and evaluated to correct for attenuation and scatter in the object in conjunction with a filtered backprojection reconstruction algorithm. A weighted-backprojection approach whereby corrections are applied to each pixel from each angle of view was used to correct for attenuation. Using a germanium detector to sample the energy spectrum of emitted radiation, an optimal method was devised to subtract scatter counts from the photopeak counts of a scintillation camera before reconstruction. SPECT (single-photon-emission computed tomography) images of the test object were evaluated to validate the correction approaches. >

Implementation of simultaneous attenuation and detector response correction in SPECT

Simultaneous correction of nonuniform attenuation and detector response was implemented in single-photon-emission computed tomography (SPECT) image reconstruction. A ray-driven projector-backprojector that exactly models attenuation in the reconstructed image slice and the spatially variant detector response was developed and used in the iterative maximum-likelihood algorithm for the correction. A computer-generated heart-lung phantom was used in simulation studies to compare the simultaneous correction method with an intrinsic attenuation correction method using a smoothing filter, and intrinsic attenuation correction method using a deconvolution filter, and a modified Chang attenuation correction method using a nonuniform attenuation distribution. The results demonstrate that the present method provides more-accurate quantitation and superior image quality.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>