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A line-source method for aligning on-board and other pinhole SPECT systems
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10.1118/1.4828776
/content/aapm/journal/medphys/40/12/10.1118/1.4828776
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/12/10.1118/1.4828776

Figures

Image of FIG. 1.
FIG. 1.

Computer-aided design illustration of a robotic multipinhole SPECT system imaging a patient in position for radiation therapy. Also shown are a patient table and LINAC. The system involves a robotic arm (KUKA Robotics Corporation, Shelby Township, MI) which maneuvers a 49-pinhole-SPECT system about the patient. This multipinhole SPECT system would concentrate detector area on a limited region of interest, e.g., the radiation-therapy target, thereby improving SPECT sensitivity for that region of interest and potentially allowing relatively short scan times.

Image of FIG. 2.
FIG. 2.

Pinhole projection of a point . The coordinates are parallel to the coordinates, with the -axis and -axis pointing into the paper. The gray dot represents a point. The gray dot on the detector represents the pinhole projection of this point. The detector translations and are the detector shifts in the -axis and -axis directions from the xyz origin. The pinhole translations and are relative to the detector center, which intercepts the -axis. The detector radius of rotation and pinhole focal length − are along the -axis direction.

Image of FIG. 3.
FIG. 3.

(a) The gray broad line segment is a single pinhole projection of a line source. The superimposed narrow dark gray line is the estimated ridge of the line-source projection and is computed using (15) , where (α, ρ) corresponds to the maximum pixel value determined from the Radon transform of the line-source projection. The offset (ρ) is the perpendicular distance from the center of the projection image to the ridge of the line-source projection. The angle (α) is between the horizontal-axis and the offset-axis. (b) Radon transform of line-source projection in (a), where (α, ρ) is the angle and offset corresponding to the maximum pixel value of the Radon transform and is used to draw the red line in (a).

Image of FIG. 4.
FIG. 4.

(a) Computer simulated line-source phantom with five line sources. (b) Projection image of the line-source phantom with pseudo random sampling from corresponding Poisson distributions.

Image of FIG. 5.
FIG. 5.

(a) Line-source phantom with Tc-99m injected in five lines. (b) Single pinhole collimated SPECT detector with line-source phantom. (c) SPECT detector attached to robotic arm imaging line-source phantom.

Image of FIG. 6.
FIG. 6.

Errors in estimating six alignment parameters for Study B using three line sources, Study C using four line sources, and Study D using five line sources (from left to right). Each distribution is obtained from 400 noisy realizations. The number above each whisker is the number of outliers. The mean of each distribution is represented by an “x”. Errors in parameter estimation from noise-free projections are represented by a “+”.

Image of FIG. 7.
FIG. 7.

Box-and-whisker plots of alignment parameter error with different activity concentration of 1.85 MBq, 7.4 MBq, and 14.8 MBq per line (from left to right). Each distribution is obtained from 400 noisy realizations. The mean of each distribution is represented by an “x”. Errors in parameter estimation from noise-free projections are represented by a “+”.

Image of FIG. 8.
FIG. 8.

Box-and-whisker plots of alignment parameter error for seven parameters with activity concentration of 14.80 MBq per line and 3.5 mm intrinsic resolution. The number above each whisker is the number of outliers. Each distribution is obtained from 400 noisy realizations. The mean of each distribution is represented by an “x”. Errors in parameter estimation from noise-free projections are represented by a “+”.

Tables

Generic image for table
TABLE I.

Simulated line source geometry used in this paper as shown in Fig. 4(a) , specified using the coefficients (a,b,c,d) of Eqs. (1) and (2) .

Generic image for table
TABLE II.

Four experiments designed to evaluate the proposed alignment procedure.

Generic image for table
TABLE III.

Four different acquisition geometries. The top first row of each acquisition geometry is the true values of alignment parameters. The true values are those used to compute the 2D line-source projections. The start points are the initial values in the iterative parameter estimation.

Generic image for table
TABLE IV.

Physical line source geometry determined in the CT (XYZ) coordinate frame from the CT image, specified using the coefficients (a,b,c,d) of Eqs. (1) and (2) .

Generic image for table
TABLE V.

Three acquisition geometries for scanner-acquired projections of the physical line-source phantom. The top first row for each acquisition geometry is the true value as given by the robot tool coordinate frame. The second row gives initial values in the iterative parameter estimation.

Generic image for table
TABLE VI.

The 25% quartile (Q1), the median quartile (Q2), and the 75% quartile (Q3) values of the estimated alignment parameters of Study B, C, and D. The highest outlier values and the percent of outliers of each estimated alignment parameters of Study B, C, and D. -values are from two-tailed Wilcoxon rank sum test with 5% significance level. Numbers in bold are < 0.05.

Generic image for table
TABLE VII.

The 25% quartile (Q1), the median quartile (Q2), and the 75% quartile (Q3) values of the estimated alignment parameters of intrinsic detector resolution of 1.5 mm, 2.5 mm, and 3.5 mm. The highest outlier values and the percent of outliers of each estimated alignment parameters. The -values are from a two-tailed Wilcoxon rank sum test with 5% significance level. Numbers in bold are < 0.05.

Generic image for table
TABLE VIII.

The 25% quartile (Q1), the median quartile (Q2), and the 75% quartile (Q3) values of the estimated alignment parameters of five line sources with 1.85 MBq, 7.40 MBq, and 14.80 MBq per line with 3.5 mm intrinsic resolution. The highest outlier values and the percent of outliers of each estimated alignment parameters. -values are from two-tailed Wilcoxon rank sum test with 5% significance level. Numbers in bold are < 0.05.

Generic image for table
TABLE IX.

The error in alignment parameters estimated from five line-source projections with physical line-source phantom using robotic pinhole SPECT system.

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/content/aapm/journal/medphys/40/12/10.1118/1.4828776
2013-11-12
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: A line-source method for aligning on-board and other pinhole SPECT systems
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/12/10.1118/1.4828776
10.1118/1.4828776
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