Angular-Dependent Axial-Shift Correction for Pinhole SPECT

Metzler, S.; Jaszczak, R.J.; Greer, K.L.; Bowsher, J.E.

doi:10.1109/tns.2006.887470

Cited by 9 publications

(7 citation statements)

References 14 publications

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“…Another method 11 was proposed that used a different optimization method to estimate six alignment parameters from two point sources and six detector views. Subsequently methods were developed for SPECT pinhole alignment, [12][13][14][15][16][17] often incorporating methods similar to those for cone-beam. Many of these methods utilize multiple pinhole projection views.…”

Section: Introductionmentioning

confidence: 99%

A line‐source method for aligning on‐board and other pinhole SPECT systems

2013

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Purpose: In order to achieve functional and molecular imaging as patients are in position for radiation therapy, a robotic multipinhole SPECT system is being developed. Alignment of the SPECT system-to the linear accelerator (LINAC) coordinate frame and to the coordinate frames of other on-board imaging systems such as cone-beam CT (CBCT)-is essential for target localization and image reconstruction. An alignment method that utilizes line sources and one pinhole projection is proposed and investigated to achieve this goal. Potentially, this method could also be applied to the calibration of the other pinhole SPECT systems. Methods: An alignment model consisting of multiple alignment parameters was developed which maps line sources in three-dimensional (3D) space to their two-dimensional (2D) projections on the SPECT detector. In a computer-simulation study, 3D coordinates of line-sources were defined in a reference room coordinate frame, such as the LINAC coordinate frame. Corresponding 2D line-source projections were generated by computer simulation that included SPECT blurring and noise effects. The Radon transform was utilized to detect angles (α) and offsets (ρ) of the line-source projections. Alignment parameters were then estimated by a nonlinear least squares method, based on the α and ρ values and the alignment model. Alignment performance was evaluated as a function of number of line sources, Radon transform accuracy, finite line-source width, intrinsic camera resolution, Poisson noise, and acquisition geometry. Experimental evaluations were performed using a physical linesource phantom and a pinhole-collimated gamma camera attached to a robot. Results: In computer-simulation studies, when there was no error in determining angles (α) and offsets (ρ) of the measured projections, six alignment parameters (three translational and three rotational) were estimated perfectly using three line sources. When angles (α) and offsets (ρ) were provided by the Radon transform, estimation accuracy was reduced. The estimation error was associated with rounding errors of Radon transform, finite line-source width, Poisson noise, number of line sources, intrinsic camera resolution, and detector acquisition geometry. Statistically, the estimation accuracy was significantly improved by using four line sources rather than three and by thinner linesource projections (obtained by better intrinsic detector resolution). With five line sources, median errors were 0.2 mm for the detector translations, 0.7 mm for the detector radius of rotation, and less than 0.5• for detector rotation, tilt, and twist. In experimental evaluations, average errors relative to a different, independent registration technique were about 1.8 mm for detector translations, 1.1 mm for the detector radius of rotation (ROR), 0.5• and 0.4• for detector rotation and tilt, respectively, and 1.2• for detector twist. Conclusions: Alignment parameters can be estimated using one pinhole projection of line sources. Alignment errors are largely associated with limite...

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Section: Introductionmentioning

confidence: 99%

A line‐source method for aligning on‐board and other pinhole SPECT systems

2013

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“…A review of recent reports shows that significant progress has been made in achieving these goals with custom-made or commercial systems incorporating various modes of SPECT imaging. Of particular interest is recent work on applications of multipinhole SPECT [1–17] and helical SPECT (HSPECT) [18–27]. …”

Section: Introductionmentioning

confidence: 99%

“…To solve the problem of axial blurring of circular-orbit pinhole SPECT, Metzler et al [18–22] reported the application of the helical orbit conventionally used in transmission computed tomography to imaging with SPECT. Sun et al [23] presented a helical SPECT scanner featuring solid-state cadmium zinc telluride (CZT) detectors.…”

Section: Introductionmentioning

confidence: 99%

A small-animal imaging system capable of multipinhole circular/helical SPECT and parallel-hole SPECT

Qian

Bradley

Majewski

et al. 2008

Nuclear Instruments and Methods in Physics Research Section A:

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We have designed and built a small animal single photon emission computed tomography (SPECT) imaging system equipped with parallel-hole and multipinhole collimators and capable of circular or helical SPECT. Copper-beryllium parallel-hole collimators suitable for imaging the ~35 keV photons from the decay of 125I have been built and installed to achieve useful spatial resolution over a range of object-detector distances and to reduce imaging time on our dual-detector array. To address the resolution limitations in the parallel-hole SPECT and the sensitivity and limited field of view of single-pinhole SPECT, we have incorporated multipinhole circular and helical SPECT in addition to expanding the parallel-hole SPECT capabilities. The pinhole SPECT system is based on a 110 mm diameter circular detector equipped with a pixellated NaI(Tl) scintillator array (1×1×5 mm3/pixel). The helical trajectory is accomplished by two stepping motors controlling the rotation of the detector-support gantry and displacement of the animal bed along the axis of rotation of the gantry. Results obtained in SPECT studies of various phantoms show an enlarged field of view, very good resolution and improved sensitivity using multipinhole circular or helical SPECT. Collimators with one, three and five 1 mm diameter pinholes have been implemented and compared in these tests. Our objective is to develop a system on which one may readily select a suitable mode of either parallel-hole SPECT or pinhole circular or helical SPECT for a variety of small animal imaging applications.

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“…It is likely that this disagreement was due to angular-dependent Manuscript axial mechanical shifts. In fact, [7] later showed that angular dependent axial mechanical shift correction improves the axial resolution. In our study, we used a smaller phantom with 9 hot disks with 1.6 mm thickness and 27 mm diameter that more closely mimics the size of a mouse.…”

Section: Introductionmentioning

confidence: 99%

“…In our study, we used a smaller phantom with 9 hot disks with 1.6 mm thickness and 27 mm diameter that more closely mimics the size of a mouse. In addition, we implemented angular-dependent axial mechanical shift correction, which has been shown previously [7], [8] to substantially improve axial resolution in this regime. The synchronized motion was achieved with a custom-designed electronic circuit.…”

Section: Introductionmentioning

confidence: 99%

Axial Resolution of Helical-Orbit Pinhole SPECT With Synchronized and Unsynchronized Motion

Ayan

Metzler

2008

IEEE Trans. Nucl. Sci.

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Pinhole SPECT imaging is widely used in small-animal imaging. Helical orbits provide better sampling and axial resolution compared to circular ones; however, the unsynchronized axial translation of the imaged object and the camera rotation may cause blurring in the image resulting in poorer resolution. In this study, we investigated the axial resolution for synchronized and unsynchronized motions with a small phantom (Ultra-Micro-Defrise) that closely mimics the size of a mouse. We applied angular-dependent axial mechanical shift corrections that substantially improved axial resolution in this regime. Further, we developed custom-designed electronic circuitry to achieve synchronization of the SPECT scanner and the imaged object. The results show that synchronized motion improves axial resolution especially when the angular step of the scanner's rotation is large.

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Angular-Dependent Axial-Shift Correction for Pinhole SPECT

Cited by 9 publications

References 14 publications

A line‐source method for aligning on‐board and other pinhole SPECT systems

A line‐source method for aligning on‐board and other pinhole SPECT systems

A small-animal imaging system capable of multipinhole circular/helical SPECT and parallel-hole SPECT

Axial Resolution of Helical-Orbit Pinhole SPECT With Synchronized and Unsynchronized Motion

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