Study of noise propagation and the effects of insufficient numbers of projection angles and detector samplings for iterative reconstruction using planar-integral data

Defrise

IEEE Trans. Med. Imaging

2010

We have previously proposed a method to compare tomographic systems. It is assumed that each system acquires a tomographic scan of a certain tracer distribution in the same acquisition time. From this scan, each system is forced to reconstruct an image with a predefined spatial resolution. The system that can perform this task with the "most favorable" noise propagation is considered as the best system. The variance on pixel values or region-of-interest (ROI) values is used to assess the noise in the reconstructed image. In this paper, we extend this idea to compare the performance of parallel hole (PH) and rotating slat (RS) collimations. Two different analytical approaches were used to analyze the variance of the reconstructed pixel/ROI values. The first method is based on the filtered-backprojection (FBP) theory, and was applied to the central point of a uniform symmetrical phantom. It yields analytical expressions for the optimal collimator aperture and the corresponding variance of the reconstructed pixel values, but it can only be applied to highly symmetrical configurations. The second method is based on approximations for the Fisher information matrix. It provides numerical results, and it is more general and can be applied to nonsymmetrical objects and shift-variant tomographic systems. The collimations were compared for both planar imaging and volume imaging. The main results are as follows. 1) For cases where both methods are valid, they are in excellent agreement. 2a) The optimal collimator aperture varies linearly with the target resolution. 2b) For a fixed target resolution, the optimal collimator aperture depends on the collimator type and the imaging mode (planar or volume). 2c) The optimal aperture of PH is a factor of √2 larger than that of RS. 3a) The relative performance of the two collimators is determined by both the object size and the object-to-detector distance. 3b) Pixel variance and variances of ROIs with varying sizes yield very similar relative performance for RS versus PH.

Section: Discussionsupporting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Comparison Between Parallel Hole and Rotating Slat Collimation: Analytical Noise Propagation Models

Defrise

IEEE Trans. Med. Imaging

2010

“…This expression is similar to those presented in several other papers [3], [7]. The main differences between our approach and others' are that we compared PH and RS at a fixed target resolution, and that we used the optimized aperture for each collimator system.…”

Section: Discussionsupporting

confidence: 56%

Comparison between parallel hole and rotating slat collimation

Defrise

2008 IEEE Nuclear Science Symposium Conference Record

et al. 2008

In this study, we compared the performance of parallel hole (PH) and rotating slat (RS) collimations at equal spatial resolution. Based on mathematical calculations, we derived the linear relationship between the optimal collimator aperture and the target spatial resolution for each collimator, and calculated the gain in signal-to-noise ratio (RS over PH) for the central point of a homogeneous symmetrical phantom using these optimized collimator parameters. These results were supported by an efficient analytical Fisher information-based method. The collimations were compared for both planar imaging and volume imaging. The main results are: 1) For the same target resolution, the optimal system resolution depends on the collimator and the imaging mode (planar or volume). 2) RS has lower variance than PH when the object is smaller than the detector.

“…The two collimator systems were first optimized and then compared using their optimized geometries. The rankings of the two collimators were in agreement with [5]- [7], but the computed performance ratios for RS versus PH collimation were different, since the optimal collimator apertures were not used in those studies.…”

Section: Introductionmentioning

confidence: 66%

Parallel Hole and Rotating Slat Collimators: Comparative Study Using Digital Contrast Phantoms

2013

IEEE Trans. Nucl. Sci.

Abstract-The parallel hole (PH) collimator is the most commonly used collimator in single photon emission computed tomography (SPECT) imaging. A well-known limitation of the PH collimator is its low geometric efficiency. For better geometric efficiency without compromising the resolution, a rotating slat (RS) collimator is a potential alternative. In our previous work, a linear relation between the image resolution and the optimal collimator aperture was derived for both the PH and the RS collimator systems, and the two collimator systems were compared with the optimized geometries using different uniform phantoms. In this study, the PH and the RS collimator system were further compared using digital contrast phantoms. Three figures of merit (FOMs) were calculated for comparison, i.e., the contrast-to-noise ratio (CNR) in a pixel of interest, the CNR in a region of interest, and the signal-to-noise ratio (SNR) of a channelized Hotelling observer (CHO). All the FOMs were calculated analytically using an efficient approximation method.The comparison was done in both planar imaging and volume imaging. The size of the digitized phantom was varied, resulting in a detector area coverage from 2.5% to 40%. The main results are: (1) With the optimal collimator apertures, the gains (RS over PH) in all FOMs show the same trends in the system comparison. (2) The performance of the two collimators is similar for cold spot imaging with the largest phantom given in this study, while RS outperforms PH for all the other cases. (3) For system optimization, the optimal collimator apertures depend on the FOM to be optimized, however the ratio of the apertures (PH/RS) is always around √ 2, a value that we derived analytically in our previous work.