Optimizing pinhole and parallel hole collimation for scintimammography with compact pixellated detectors

Abstract

Abstract-The relative advantages of pinhole and parallel hole collimators for scintimammography with compact, pixellated gamma detectors were investigated using analytic models of resolution and sensitivity. Collimator design was studied as follows. A desired object resolution was specified for a pixellated detector with a given crystal size and intrinsic spatial resolution and for a given object-to-collimator distance. Using analytic formulas, pinhole and parallel hole collimator parameters were calculated that satisfy this object resolution with optimal geometric sensitivity. Analyses were performed for 15 cm x 20 cm field of view detectors with crystal elements 1.0, 2.0 and 3.0 mm on a side and 140 keV incident photons. The sensitivity for a given object resolution was greater for pinhole collimation at smaller distances, a s expected. The object distance at which the pinhole and parallel hole sensitivity curves cross each other is important. The crossover distances increased with larger crystal size for a constant object resolution and increased as the desired object resolution decreases for a constant crystal size. For example, for 4 mm object resolution these distances were 5.5 cm, 6.5 cm and 8 cm for the 1 mm, 2 mm and 3 mm crystal detectors, respectively. The results suggest a strategy of parallel hole collimation for whole breast imaging and pinhole collimation for imaging focal uptake. This could be accomplished with a dual detector system with a different collimator type on each head or a single head system equipped with two collimators and a rapid switching mechanism. Multipinhole collimators have the potential to increase sensitivity yet maintain high image resolution. An experimental SPECT phantom study with a four-pinhole collimator was acquired with a pixellated detector. The iterative maximum-likelihood expectationmaximization (MLEM) reconstruction of a hot sphere in a warm cylinder showed the potential of multipinhole collimation to improve sensitivity for tomographic pinhole scintimammography.

Slit-Slat and Multi-Slit-Slat Collimator Design and Experimentally Acquired Phantom Images From a Rotating Prototype

“…The values of $\overline{g_{ss}}$, as calculated in (10), and $\overline{g_{pb}}$, as calculated using the methods in [14], are shown for different values of isotropic resolution (4, 5 and 10 mm) at the center of the object using an intrinsic resolution R i = 3.5 mm and c = 10 mm as a function of D in Fig. 7 for transaxial detector sizes of 40 cm and 54 cm.…”

“…The value of t is chosen to be sufficiently large to keep septal penetration reasonably small [14]. However, large values of t reduce geometric efficiency through the packing-fraction factor, d /( d + t ).…”

“…The maximum value of $\overline{g_{pb}}$ was obtained using the methods in [14], which also maximizes sensitivity under the constraints of a desired, fixed resolution at the center and limited septal penetration, with the additional constraint that t ≥ 0.1 mm for mechanical stability; this same constraint is applied to slit-slat collimation.…”

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

“…The new CuBe collimator (Collimator #2) measures 6 mm thick with 0.3×0.3 mm 2 openings and 0.05 mm septa. Collimator dimensions were determined with the formulae of Keller [37] and Smith et al [38] The efficiency and spatial resolution of the new compact gamma camera were measured with a single capillary phantom with an inner diameter of 0.3 mm containing an activity of 0.37 MBq in 8 cm length. The capillary phantom was imaged for 10 min at a distance 4 mm, 17 mm, 32 mm, 47 mm and 62 mm from the detector.…”

Design and evaluation of a breast specific collimator using response surface methodology and Monte Carlo simulations

“…Thus, design optimization of collimators for various cameras and scanning procedures has been a challenge for many years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”