Beam Reconstruction Research Articles

Reliability of cone beam computed tomography in scalar localization of the electrode array: a radio histological study

Postoperative imaging plays a growing role in clinical studies concerning prognostic factors in cochlear implantation. Indeed, intracochlear position of the cochlear implant has recently been identified as a contributor in functional outcomes and radiological tools must be accurate enough to determine the final placement of the electrode array. The aim of our study was to validate cone beam computed tomography as a reliable technique for scalar localization of the electrode array. We performed therefore a temporal bone study on ten specimens that were implanted with a perimodiolar implant prototype. Cone beam reconstructions were performed and images were analyzed by two physicians both experienced in cochlear implant imaging, who determined the scalar localization of the implant. Temporal bones then underwent histological control to document this scalar localization and hypothetical intracochlear lesions. In four cases, a dislocation from scala tympani to scala vestibuli was suspected on cone beam reconstructions of the ascending part of the basal turn. In three of these four specimens, dislocation in pars ascendens was confirmed histologically. In the remaining temporal bone, histological analysis revealed an elevation with rupture of the basilar membrane. Histological assessment revealed spiral ligament tearing in another bone. We conclude that cone beam is a reliable tool to assess scalar localization of the selectrode array and may be used in future clinical studies.

X-ray wavefront characterization of a Fresnel zone plate using a two-dimensional grating interferometer

The x-ray wavefront downstream of a Fresnel zone plate (FZP) was characterized using a two-dimensional grating interferometer. Transverse wavefront slope maps, measured using a raster phase-stepping scan, allowed accurate phase reconstruction of the x-ray beam. Wavefront measurements revealed that the wavefront error is very sensitive to the input beam entering the FZP. A small stack of one-dimensional compound refractive lenses was used to introduce astigmatism in the probing x-ray beam to investigate the contribution of the incoming beam in contrast to the optical aberrations. Experimental data were shown to be consistent with theoretical calculations.

Relating Noise to Image Quality Indicators in CT Examinations With Tube Current Modulation

Modern CT systems use surrogates of noise-noise index (NI) and quality reference effective tube current-time product (Q)-to infer the quality of images acquired using tube current modulation. This study aimed to determine the relationship between actual noise and these surrogates for two CT scanners from two different manufacturers. Two phantoms (adult and 1-year-old child) were imaged on two CT scanners (64 and 128 MDCT) using a clinical range of NI (6-22) and Q (30-300 mA). Each scan was performed twice, and noise was measured in the mediastinum, lung, and abdomen using an image subtraction technique. The effect on noise from changing other imaging parameters, such as beam collimation, pitch, peak kilovoltage, slice thickness, FOV, reconstruction kernel or algorithm, and patient age category (adult or pediatric), was investigated. On the 64-MDCT scanner, noise increased linearly along with NI, with the slope affected by changing the anatomy of interest, peak kilovoltage, reconstruction algorithm, and convolution kernel. The noise-NI relationship was independent of phantom size, slice thickness, pitch, FOV, and beam width. On the 128-MDCT scanner, noise decreased nonlinearly along with increasing Q, slice thickness, and peak tube voltage. The noise-Q relationship also depended on anatomy of interest, phantom size, age selection, and reconstruction algorithm but was independent of pitch, FOV, and detector configuration. We established how noise changes with changing image quality indicators across a clinically relevant range of imaging parameters. This work can aid in optimizing protocols by targeting specific noise levels for different types of CT examinations.

State reconstruction of a multimode twin beam using photodetection

Robust and reliable method for reconstructing quasi-distributions of integrated intensities of twin beams generated in spontaneous parametric down-conversion and entangled in photon numbers is suggested. It utilizes the first and second photocount moments and minimizes the declination from experimental photocount histograms. Qualitatively different forms of quasi-distributions for quantum and classical states are suggested in the method. The transition from quantum to classical states caused by an increased detection noise is discussed. Momentum criterion for non-classicality of twin beams is suggested.

Temporal evolution of administered activity in cardiac gated SPECT and patients’ effective dose: analysis of an historical series

Myocardial perfusion imaging contributes >20% of the average medical radiation exposure to the population in the USA. Imaging protocols able to achieve a radiation exposure ≤9mSv in 50% of the studies by 2014 have been recommended. The aim of this study was to analyse the temporal evolution of administered activities in patients scheduled for dual-day (99m)Tc tracer gated single photon emission computed tomography (SPECT) and to compare different dose administration protocols in terms of patients' effective dose. Patients evaluated from 1 July 2002 to 31 January 2012 were allocated according to the protocol adopted: group 1: fixed activity according to diagnostic reference level: 740MBq up to 80kg (adapted for weight <60kg); 900MBq 80-100kg, 1,110MBq >100kg, standard filtered back-projection (FBP) reconstruction; group 2: weight-adjusted activity: 8MBq/kg up to 1,110MBq, standard FBP reconstruction; and group 3: 4MBq/kg, UltraSPECT wide beam reconstruction (WBR) reconstruction. A dual-head Anger camera (GE Helix) was used. A total of 9,060 patients were allocated to different groups: 4,751 in group 1, 2,844 in group 2 and 1,465 in group 3. The stress + rest administered activity was 1,617 ± 180 in group 1, 1,136 ± 260 in group 2 and 682 ± 164MBq in group 3 (all p < 0.001). Patients' effective dose was 13.7 ± 3 in group 1, 9.5 ± 2.8 in group 2 and 5.7 ± 1.6mSv in group 3 (all p < 0.001). The 50th percentile was 12.6 in group 1, 9.1 in group 2 and 5.3mSv in group 3. The effective dose received by the dedicated cardiologists was 2.1, 1.5 and 1.0μSv/exam in group 1, group 2 and group 3 periods, respectively (all p < 0.001). A significant reduction over time in the administered activity for gated SPECT was achieved; accordingly, a significant reduction in patients' exposure was obtained. A simple weight-adjusted strategy with 8MBq/kg immediately fulfils the recommendations to limit exposure. In selected group 3 patients, a stress-only strategy allows for studies with <3mSv exposure. Thus, at least the adoption of a new reconstruction algorithm is strongly encouraged, and suggested tracer activities for cardiac gated SPECT are to be revised.

Very low-activity stress/high-activity rest, single-day myocardial perfusion SPECT with a conventional sodium iodide camera and wide beam reconstruction processing

BackgroundA stress (S)/rest (R) 1-day Tc-99m sestamibi protocol is logistically advantageous and facilitates stress-only imaging. However, with conventional 370 MBq (10 mCi) S activity and subsequent 1,110-1,295 MBq (30-35 mCi) R activity there is a risk of S-to-R “shine-through” and underestimation of defect reversibility. New software methods cope with lower counting statistics and should allow for both a reduced S activity and also less likelihood of S-to-R “shine-through.” Methods102 prospective patients [49 men, 53 women; mean weight 178 ± 41 lbs (range 98-265 lbs); chest 41.5″ ± 4.0″ (range 32″-52″)] received 192.4 + 18.5 MBq (5.2 ± 0.5 mCi) Tc-99m sestamibi S (25 exercise, 77 regadenoson) activity followed in 30-40 minutes by “full-time” (12 minutes) two-headed NaI camera S SPECT. Immediately thereafter, a 16-minute S SPECT acquisition was also performed in 37/102 patients. Then at 60-80 minute post-S all patients received 1328.3 + 129.5 MBq (35.9 ± 3.5 mCi) Tc-99m sestamibi, and “half-time” (7.5 minutes) R SPECT was acquired. All tomograms were processed with wide beam reconstruction (WBR, UltraSPECT Ltd.) software. A time-adjusted R/S myocardial count density ratio (MCDR) was calculated using automated software. S SPECT quality was visually graded (poor, fair, good, excellent) based upon myocardial definition, cavity contrast, RV visualization, and noise. For comparison, the S/R MCDR was calculated in 581 consecutive patients undergoing a conventional 370 MBq R/1110 MBq S (10 mCi R/30 mCi S) protocol. ResultsS SPECT was normal in 44 patients (43%). Image quality was good-excellent in 93 (91%) patients with 12-minute S SPECT. Also in 37 (98%) patients with 16-minute S SPECT, quality was good-excellent. In patients with >42″ chests 12-minute S SPECT quality worsened with increasing chest circumference, manifested by myocardial “blurring.” Image quality improved by ≥1 grade in the 12/37 patients (32%) also undergoing 16-minute S SPECT. The time- and decay-corrected 12-minute mean R/S MCDR was 5.78, a ratio adequate to minimize S-to-R shine-through, as verified in phantom experiments, and significantly better than a 3.79 S/R ratio achieved in the 581 patients undergoing a conventional R/S protocol. ConclusionsAn approximately 185 MBq (5 mCi S) Tc-99m SPECT processed with WBR provides adequate image quality. For larger patients prolonging image acquisition to 16 minutes is beneficial. For patients with normal S SPECT, a S-only protocol is feasible, affording them a very low (approximately 1.4 mSv) radiation dose. If subsequent R SPECT is necessary, it can be performed with approximately 1,332 MBq (36 mCi) with minimal S-R “shine-through.”

TU‐A‐BRB‐10: Ultrasonic Imaging of Dose to Water from a 1.5 MeV Electron Beam

Purpose: To use an ultrasonic sensor array to obtain thermal images produced by absorbed ‐dose distributions in a water phantom. Method and Materials: An array of 128 PVDF ultrasonic transducers arranged in a circle with radius 177.8 mm is used to image the heating of water in a phantom irradiated by a vertical, 1.5 ‐MeV electron beam capable of delivering dose rates ranging from Gy/min to kGy/min. Fan ‐beam sampling and reconstruction are managed by a double ‐multiplexer system that selects one transducer to emit a short pulse and scans the corresponding transducers across the tank to receive the propagated pulse. Time ‐of ‐flight measurements between transmitter/receiver pairs are then converted to temperature and passed to a filtered back projection algorithm to reconstruct the desired thermal distributions. Since dose from the beam is deposited mostly within the top cm layer of water, the array is located just below the water surface. A small, 4 ‐cm diameter Al mask is placed just above the water surface to aperture the beam. Results: Preliminary measurements involving therapy ‐level radiation were obscured by system noise, but higher doses, of order 1000 Gy/min, produced detectable images within seconds. Conclusion: Imaging of absorbed dose to water has been achieved for the first time, although at dose rates that are considerably above therapy level. Planned improvements in signal processing are expected to bring the detection limit into the therapy regime. Other uses of the array, e.g. triangulation of thermoacoustic disturbances caused by pulsed radiation sources, are also being investigated.

Scatter correction in cone‐beam CT via a half beam blocker technique allowing simultaneous acquisition of scatter and image information

X-ray scatter incurred to detectors degrades the quality of cone-beam computed tomography (CBCT) and represents a problem in volumetric image guided and adaptive radiation therapy. Several methods using a beam blocker for the estimation and subtraction of scatter have been proposed. However, due to missing information resulting from the obstruction of the blocker, such methods require dual scanning or dynamically moving blocker to obtain a complete volumetric image. Here, we propose a half beam blocker-based approach, in conjunction with a total variation (TV) regularized Feldkamp-Davis-Kress (FDK) algorithm, to correct scatter-induced artifacts by simultaneously acquiring image and scatter information from a single-rotation CBCT scan. A half beam blocker, comprising lead strips, is used to simultaneously acquire image data on one side of the projection data and scatter data on the other half side. One-dimensional cubic B-Spline interpolation/extrapolation is applied to derive patient specific scatter information by using the scatter distributions on strips. The estimated scatter is subtracted from the projection image acquired at the opposite view. With scatter-corrected projections where this subtraction is completed, the FDK algorithm based on a cosine weighting function is performed to reconstruct CBCT volume. To suppress the noise in the reconstructed CBCT images produced by geometric errors between two opposed projections and interpolated scatter information, total variation regularization is applied by a minimization using a steepest gradient descent optimization method. The experimental studies using Catphan504 and anthropomorphic phantoms were carried out to evaluate the performance of the proposed scheme. The scatter-induced shading artifacts were markedly suppressed in CBCT using the proposed scheme. Compared with CBCT without a blocker, the nonuniformity value was reduced from 39.3% to 3.1%. The root mean square error relative to values inside the regions of interest selected from a benchmark scatter free image was reduced from 50 to 11.3. The TV regularization also led to a better contrast-to-noise ratio. An asymmetric half beam blocker-based FDK acquisition and reconstruction technique has been established. The proposed scheme enables simultaneous detection of patient specific scatter and complete volumetric CBCT reconstruction without additional requirements such as prior images, dual scans, or moving strips.

Nonlinear light-matter interaction with femtosecond high-angle Bessel beams

We show that high-angle Bessel beams may significantly reduce nonlinear pulse distortions due, for example, to nonlinear Kerr effects (self-phase-modulation and self-focusing) yet enhance ionization and plasma generation. Holographic reconstruction of Bessel beams in water show intensity clamping at increased intensities and evidence of nontrivial plasma dynamics as the input energy is increased. The solvated electron density increases significantly and the cavitation-induced bubbles are ejected from the focal region indicating a significant excess plasma heating in the Bessel-pulse wake.

Simulation and experimental confirmation on the reconstruction of Bessel beams

The reconstruction property of the Bessel beam plays a significant role in the application of multi-plane micro-manipulation. We analyze the principle of the generation and the reconstruction of Bessel beam according to the Hankel wave theory; we also discuss the reconstructions of circular and square obstacles on-axial and off-axial of system in detail respectively. The generation of Bessel by axicon and the self-reconstruction property of Bessel beam after different kinds of obstacles are simulated by optical design software ZEMAX. Experimental result is used to confirm the simulation model, and it accords with the simulation very well. Therefore, we obtain a conclusion that the software ZEMAX can quickly and intuitively simulate the reconstruction of Bessel beam generated by axicon with high veracity.

Influence of acquisition parameters on MV‐CBCT image quality

The production of high quality pretreatment images plays an increasing role in image‐guided radiotherapy (IGRT) and adaptive radiation therapy (ART). Megavoltage cone‐beam computed tomography (MV‐CBCT) is the simplest solution of all the commercially available volumetric imaging systems for localization. It also suffers the most from relatively poor contrast due to the energy range of the imaging photons. Several avenues can be investigated to improve MV‐CBCT image quality while maintaining an acceptable patient exposure: beam generation, detector technology, reconstruction parameters, and acquisition parameters. This article presents a study of the effects of the acquisition scan length and number of projections of a Siemens Artiste MV‐CBCT system on image quality within the range provided by the manufacturer. It also discusses other aspects not related to image quality one should consider when selecting an acquisition protocol. Noise and uniformity were measured on the image of a cylindrical water phantom. Spatial resolution was measured using the same phantom half filled with water to provide a sharp water/air interface to derive the modulation transfer function (MTF). Contrast‐to‐noise ratio (CNR) was measured on a pelvis‐shaped phantom with four inserts of different electron densities relative to water (1.043, 1.117, 1.513, and 0.459). Uniformity was independent of acquisition protocol. Noise decreased from 1.96% to 1.64% when the total number of projections was increased from 100 to 600 for a total exposure of 13.5 MU. The CNR showed a∓5% dependence on the number of projections and 10% dependence on the scan length. However, these variations were not statistically significant. The spatial resolution was unaffected by the arc length or the sampling rate. Acquisition parameters have little to no effect on the image quality of the MV‐CBCT system within the range of parameters available on the system. Considerations other than image quality, such as memory storage, acquisition speed, and individual projection image quality, speak in favor of the use of a coarse sampling rate on the short scan.PACS numbers: 87.57.C‐; 87.57.nf

Rigorous Proofs For Cone-Beam Reconstruction

Cone beam reconstruction is a three-dimensional tomographic reconstruction technique with the potential capability of producing images with temporal contrast, and three-dimensional spatial resolution.In this paper we present a rigorous proof of the novel three-dimensional inversion formula developed by B. Smith and derive strict tipper bound« for the error

High-quality 3D correction of ring and radiant artifacts in flat panel detector-based cone beam volume CT imaging

The use of an x-ray flat panel detector is increasingly becoming popular in 3D cone beam volume CT machines. Due to the deficient semiconductor array manufacturing process, the cone beam projection data are often corrupted by different types of abnormalities, which cause severe ring and radiant artifacts in a cone beam reconstruction image, and as a result, the diagnostic image quality is degraded. In this paper, a novel technique is presented for the correction of error in the 2D cone beam projections due to abnormalities often observed in 2D x-ray flat panel detectors. Template images are derived from the responses of the detector pixels using their statistical properties and then an effective non-causal derivative-based detection algorithm in 2D space is presented for the detection of defective and mis-calibrated detector elements separately. An image inpainting-based 3D correction scheme is proposed for the estimation of responses of defective detector elements, and the responses of the mis-calibrated detector elements are corrected using the normalization technique. For real-time implementation, a simplification of the proposed off-line method is also suggested. Finally, the proposed algorithms are tested using different real cone beam volume CT images and the experimental results demonstrate that the proposed methods can effectively remove ring and radiant artifacts from cone beam volume CT images compared to other reported techniques in the literature.

SU-E-T-752: Energy Spectrum and Fluence Reconstruction of High Energy Photon Beams Based on Analytical Double-Source Model

Purpose: To improve the accuracy on unfolding photon energy spectra and fluence for dose calculation, by use of measured percentage depth dose and off-axis ratio, an analytical double-source model considered both photon beam and electron contamination was constructed, an improvement of Schiff formula and finite-size pencil beam (FSPB) model. Methods: For energy spectrum reconstruction, several regression algorithms were used to obtain the optimum solution. It was also compared with the mono-source model that ignored the electron contamination. For energy fluence reconstruction, the double-source FSPB was developed by considering the energy spectra of photon beam and electron contamination, and was also reconstructed by above algorithms. Results: A representative testing sample, the AAPM 55# report as an 18MVˈs AECL Therac-20 medical linac, was used. The comparison between the double-source model and mono-source model in energy spectrum reconstruction found that there was a great improvement in accuracy; the mean error of double-source model was about 0.015% while the mono-source modelˈs was about 0.1%. We found that there are two peaks at 2 and 3 MeV in the photon energy spectra and the peak of the electron energy was in the low energy. We also found that if ignoring the electron contamination, the peak of the photon energy spectra could drift to the lower energy, and the mean error became great. We also obtained the accurate energy fluence, only about 0.01% mean error in the field. Conclusions: This study has revealed the great improvement of Schiff formula and FSPB model on energy spectrum and fluence of photon beam and electron contamination by reconstruction method, an analytical double-source model. Our finding will help know more about detail of medical linac, and improve the dose accuracy in dose calculation of radiotherapy by use of this reconstructed information. Supported by the National Natural Science Foundation under grant No.30900386 and the Anhui Provincial Natural Science Foundation under grantNo. 090413095 and 11040606Q55.

SU‐E‐J‐182: Development of a Tomosynthesis Algorithm to Reduce Cone Beam Imaging Dose

Purpose: To develop a tomosynthesis cone beam reconstruction algorithm for LINAC cone beam CT with the goal to achieve a dose reduction better than 1/5 in current cone beam imaging protocols for patient positioning and portal beam verification while maintaining the required image quality for patient positioning and beam delivery verification. Methods: Tomosynthesis is the process of reconstructing tomographic images with fewer acquired projection images and additional synthetically generated projections to preserve image resolution and contrast. We developed a tomosynthesis cone beam reconstruction algorithm based on combining Feldkampˈ s cone beam reconstruction algorithm and an iterative maximum likelihood reconstruction algorithm. The Feldkamp method is used to reconstruct the first estimate of the tomographic data and the iterative maximum likelihood algorithm improves the resolution, contrast and considerably eliminates ghost images from the first estimate. Results: The algorithm tests show image reconstruction with the adequate image quality, contrast and resolution for patient positioning and beam delivery verification with a 1/8 dose delivered reduction using current cone beam imaging set‐up protocols. Imaging time is reduced with the same proportion allowing higher patient throughput. The algorithm has been tested using patient data for head and neck and brain treatment sites. On both treatment sites, portal beam and patient localization can be effectively performed within 3 mm accuracy using digitally reconstructed radiographs generated from the tomosynthesis reconstructed patient anatomical image. The reconstruction is executed on a desktop computer with 2GHz CPU and 4 Gb RAM in less than 5 minutes. Conclusions: We developed a tomosynthesis algorithm capable of reconstructing images with adequate resolution to perform beam delivery verification and patient positioning. This dose reduction will allow the daily use of cone beam CT in patients that require daily set‐up verification which currently is impractical because of dose and time constraints.

SU‐C‐301‐04: Development of Iterative Image Reconstruction Algorithm for TBCT System

Purpose: Tetrahedron Beam Computed Tomography (TBCT) circumvents some problems of cone beam CT (CBCT) but still shares the same approximate reconstruction artifact with FDK algorithm. Recently, iterative image reconstruction has been widely employed in diagnostic CT scanners in order to suppress noise and reduce imaging dose. In this study we developed an iterative TBCT image reconstruction algorithm which is able to mitigate the cone beam reconstruction artifact as well as reduce image noise. Methods: Simultaneous algebraic reconstruction technique (SART) image reconstruction algorithms were developed based on our TBCT benchtop geometry. The algorithms were tested using both numerical and physical phantoms. The projection matrix was calculated using a distance driven method. Noise levels in reconstructed images were quantified. The approximate image reconstruction artifact at larger cone angle was evaluated. Results: With the same numerical and real scanned projection data, SART algorithm produces similar spatial resolution as the FDK algorithm. The cone artifact was significantly reduced as compared with FDK algorithm. The noise levels were reduced 16–20% by the iterative algorithm at different regions of the images. Conclusions: Iterative reconstruction algorithm further improves the image quality of the TBCT system. TBCT system with SART image reconstruction algorithm potentially may be used as a mobile CT scanner for diagnostics.This work is partially supported by NIH grant 1R21CA130330‐01A1 and DOD Prostate Cancer Research Program W81XWH‐07‐0083.

A comparison of the image quality of full-time myocardial perfusion SPECT vs wide beam reconstruction half-time and half-dose SPECT

ObjectivesWide Beam Reconstruction (WBR) (UltraSPECT, Ltd) uses resolution recovery and noise modeling to cope with decreased SPECT count statistics. Because WBR processing reconstructs half the usual SPECT count statistics, we postulate that image quality equivalent to a full-time acquisition can be achieved in either half the time or with half the radiopharmaceutical activity. MethodsIn 156 consecutive patients (pts) rest and 8-frame gated post-stress myocardial perfusion SPECT was performed following 333-444 and 1184-1480 MBq (9-12 and 32-40 mCi) Tc-99m sestamibi injections, respectively, with full-time (rest = 14 min; stress = 12.3 min) acquisitions processed with OSEM and also separate “half-time” acquisitions processed with WBR. A subsequent group of 160 consecutive pts matched in gender, weight, and chest circumference received “half-dose” rest and stress injections 214.6 ± 22.2 and 647.5 ± 92.5 MBq (5.8 ± 0.6 and 17.5 ± 2.5 mCi) with full-time SPECT acquisitions. Image quality (1 = poor to 5 = excellent) was judged by myocardial count density and uniformity, endocardial edge definition, perfusion defect delineation, right ventricular visualization, and background noise. ResultsMean image quality for rest, stress, and post-stress gated images were 3.6 ± 0.7, 3.8 ± 0.7, and 3.9 ± 1.0, respectively, for “full-time OSEM; 3.7 ± 0.8, 4.0 ± 0.7, and 4.8 ± 0.4 for “half-time” WBR; and 4.3 ± 0.8, 4.6 ± 0.6, and 4.7 ± 0.6 for “half-dose” WBR. “Half-time” and “half-dose” WBR image quality were both superior to standard full-time OSEM (P’s < .001). There was no significant difference between the summed stress and rest scores for “full-time” OSEM vs “half-time” WBR in 82 patients with perfusion defects. ConclusionsBoth “half-time” and “half-dose” WBR provide myocardial perfusion SPECT quality superior to full-time OSEM, with an associated decrease in scan acquisition time and patient radiation exposure, respectively.

环形障碍物后的无衍射光重建产生局域空心光束

环形障碍物后的无衍射光重建产生局域空心光束

环形障碍物后的无衍射光重建产生局域空心光束

环形障碍物后的无衍射光重建产生局域空心光束

Wide beam reconstruction for half-dose or half-time cardiac gated SPECT acquisitions: optimization of resources and reduction in radiation exposure

A new iterative reconstruction algorithm (WBR™) has been recently proposed for cardiac single photon emission computed tomography (SPECT). The WBR™ technology is designed to reduce noise, improving lesion identification without affecting the image resolution, allowing SPECT studies with reduced count statistic. This allows for either half-time (HT) or half-dose (HD) cardiac SPECT, with image quality and quantitative data comparable to standard-time (ST) or standard-dose (SD) SPECT. Few data exist on the comparison between conventional filtered backprojection (FBP) and this new algorithm in a clinical setting. The aim of this study was to compare the performance of FBP and WBR™. Phantoms studies were performed to compare spatial resolution and contrast recovery with FBP, ordered subset expectation maximization (OSEM) and WBR™. A group of 92 patients, with different cardiac pathology, scheduled for a stress-rest SPECT were studied: 52 patients (group A) were injected with a SD of tracer and underwent both ST and HT SPECT; 40 patients (group B) were injected with a half dose of tracer and underwent ST SPECT and immediately after an additional SPECT at double time/projection (DT), to compensate for the low count statistic. A 2-day (99m)Tc-sestamibi protocol was used in all patients. SD/ST and HD/DT SPECT were reconstructed with a conventional FBP; SD/HT and HD/ST SPECT were reconstructed with WBR™. The summed stress score (SSS) and summed rest score (SRS) were calculated; the left ventricular ejection fraction (LVEF) was automatically derived. In group A (SD), no significant differences were observed between ST FBP SPECT and HT WBR™ in SSS (11.1 and 11.7, respectively) and SRS (9.4 and 10.3, respectively, NS). LVEF on rest acquisitions was also comparable (50% on ST SPECT and 49% on HT SPECT, NS); LVEF on post-stress studies in HT SPECT (46%) was lower than ST SPECT (50%), although not statistically significant. In group B (HD), SSS (6.2 in ST and 5.3 in DT) and SRS (4.0 in ST and 3.3 in DT) were also comparable. No differences were documented between ST and DT in rest (47 and 48%, respectively) and stress (48 and 50%, respectively) LVEF. WBR™ performance and image quality were comparable to those of conventional FBP, allowing for either HT or HD studies. The former allows for an increased patient throughput and optimization of resources. The latter modalities would allow for a significant reduction in both patients' and operators' exposure. Further studies are needed to validate the clinical use of this method.