Improved image quality in pinhole SPECT by accurate modeling of the point spread function in low magnification systems. Issue 2 (14th January 2015)

• Record Type: Journal Article
• Authors: Pino, Francisco; Roé, Nuria; Aguiar, Pablo; Falcon, Carles; Ros, Domènec; Pavía, Javier
• Is Part Of: Medical physics. Volume 42:Issue 2(2015)
• Page Start: 703
• Page End: 714
• Publication Date: 2015-01-14
• Subjects: Gaussian distribution -- image reconstruction -- image resolution -- iterative methods -- medical image processing -- optical transfer function -- phantoms -- single photon emission computed tomography; Single photon emission computed tomography (SPECT) -- Spatial resolution -- Reconstruction -- Numerical approximation and analysis -- Distribution theory and Monte Carlo studies; Biological material, e.g. blood, urine; Haemocytometers -- Digital computing or data processing equipment or methods, specially adapted for specific applications -- Image data processing or generation, in general -- Scintigraphy -- Measuring radioactive content of objects, e.g. contamination (whole‐body counters G01T011/63); pinhole -- modeling PSF -- image quality -- SPECT -- quantification -- small animal; Image reconstruction -- Collimators -- Single photon emission computed tomography -- Image sensors -- Medical image noise -- Contrast sensitivity -- Cameras -- Image detection systems -- Spatial resolution; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4905157
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: Single photon emission computed tomography (SPECT) has become an important noninvasive imaging technique in small‐animal research. Due to the high resolution required in small‐animal SPECT systems, the spatially variant system response needs to be included in the reconstruction algorithm. Accurate modeling of the system response should result in a major improvement in the quality of reconstructed images. The aim of this study was to quantitatively assess the impact that an accurate modeling of spatially variant collimator/detector response has on image‐quality parameters, using a low magnification SPECT system equipped with a pinhole collimator and a small gamma camera. Methods: Three methods were used to model the point spread function (PSF). For the first, only the geometrical pinhole aperture was included in the PSF. For the second, the septal penetration through the pinhole collimator was added. In the third method, the measured intrinsic detector response was incorporated. Tomographic spatial resolution was evaluated and contrast, recovery coefficients, contrast‐to‐noise ratio, and noise were quantified using a custom‐built NEMA NU 4–2008 image‐quality phantom. Results: A high correlation was found between the experimental data corresponding to intrinsic detector response and the fitted values obtained by means of an asymmetric Gaussian distribution. For all PSF models, resolution improved as the distance from the point source to the center of the field of view increased and when the acquisition radius diminished. An improvement of resolution was observed after a minimum of five iterations when the PSF modeling included more corrections. Contrast, recovery coefficients, and contrast‐to‐noise ratio were better for the same level of noise in the image when more accurate models were included. Ring‐type artifacts were observed when the number of iterations exceeded 12. Conclusions: Accurate modeling of the PSF improves resolution, contrast, and recovery coefficients in the reconstructed images. To avoid the appearance of ring‐type artifacts, the number of iterations should be limited. In low magnification systems, the intrinsic detector PSF plays a major role in improvement of the image‐quality parameters.