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Reconstruction of Dynamic Renal Tomographic Data Acquired by Slow Rotation

Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California; Radiology Department, University of Utah, Salt Lake City, Utah; and Vancouver Hospital and Health Sciences Centre, Vancouver, British Columbia, Canada

View larger version (42K): [in a new window]   FIGURE 1. Comparison of true time–activity curves and curves obtained from reconstructions of left and right kidneys (LK and RK, respectively) (A) and backgrounds (LB and RB, respectively) (B). (A and B) Kidney and background time–activity curves were obtained using only detector 1 (Fig. 3A). (C and D) Time–activity curves of LK and background obtained with >1 detector. Number 1, 2, or 3 indicates which detector was used in reconstruction. Only every third time point is shown when symbols are used.

View larger version (37K): [in a new window]   FIGURE 2. (A) Phantom used in computer simulations. Bright small ellipses correspond to simulated kidneys. Large ellipse representing body outline is divided into left body background (LB) and right body background (RB), which have different intensity levels (shown as different shades). Rectangles encompass ROIs used for time–activity curve extractions. (B) Image of left kidney (LK) in canine study superimposed on attenuation map approximately 4 min after injection. Rectangular regions correspond to ROIs used for extraction of time–activity curves of LK (small 3-pixel ROI) and background (large 50-pixel ROI). Dog was positioned off-center during experiment.

View larger version (23K): [in a new window]   FIGURE 3. Diagram of acquisition protocols used in computer simulations (A) and experimental canine 99mTc-MAG3 renal study (A) and experimental patient 99mTc-MAG3 renal study (B). (A) In first phase of acquisition, 3-detector camera rotated from I to II in clockwise direction and acquired 60 projections for 8 s each over 180°. Camera was then returned to starting position (I) and, during second phase, it rotated in clockwise direction and acquired 60 projections for 16 s each over 180°. (B) For patient protocol, camera in first phase of acquisition rotated 90° clockwise and acquired 64 projections (from I to II). During second phase, it rotated back (from II to I) in counterclockwise direction and acquired 64 additional projections. Duration of all projections in patient study was 10 s. Number of dots indicates detector number.

View larger version (54K): [in a new window]   FIGURE 4. Summed images of planar studies for canine study (A) and for patient study (B). Black lines on images correspond approximately to slices that were reconstructed using SPECT.

View larger version (23K): [in a new window]   FIGURE 5. Time–activity curves obtained in canine study for LK. (A) Comparisons of reconstructions made with 1, 2, and 3 detectors. (B) Curves of LK derived from reconstructions made with 3-head camera with different values of parameter S. (C) Background curves reconstructed using data from 3 detectors (123) and with parameter S = 3; 3 curves correspond to 3 different ROIs. Only every third time point is shown when symbols are used.

View larger version (43K): [in a new window]   FIGURE 6. Reconstructed factors and factor coefficients of patient study. (A and D) Background. (B) Activity in kidney cortex. (C) Activity in kidney pelvis. (E) Time–activity curve (TAC) of RK, which is combination of A through D. Gap in data corresponds to time needed for detector configuration (Fig. 3B) to reset between phase 1 and phase 2 of acquisition.

View larger version (11K): [in a new window]   FIGURE 7. Example of ambiguity of reconstruction from 1-detector system. (A) Two objects (1 and 2) and detector head taking projection at time t. Objects overlap in this projection. Time–activity curves of these objects (B) result in set of projections identical to those that correspond to time–activity curves in C. Thus, reconstruction from such projections is ambiguous.