Slit-Slat and Multislit-Slat Collimator Design and Experimentally Acquired Phantom Images from a Rotating Prototype.
We have previously found and validated expressions for slit-slat (SS) geometric efficiency and resolution. These expressions have suggested that SS may be a good choice for imaging mid-size objects or objects that are long axially since (i) the geometric efficiency increases near the slit as h(-1) (instead of h(-2) for pinhole (PIN) and either decreases near the collimator for fan-beam (FB) or remains constant for parallel-beam (PB)), where h is the distance from a point to the slit plane; (ii) the transverse resolution is comparable to that of PIN, which is better than that of FB and PB for small objects; (iii) the axial resolution is worse than that of PIN since there is no axial magnification; (iv) there is a large axial FOV, unlike PIN, which is likely to be useful when imaging mid-size or long objects; and (v) there is no need for 3D orbits (e.g., helical) since each slice is complete (like PB and FB).We have developed a rotating prototype SS collimator that is capable of single-slit or multi-slit acquisition of data. The focal length (FL) is shorter than that of a typical PIN since increasing the FL requires taller slats to maintain resolution; taller slats reduce geometric efficiency. A lead rectangular box was used to provide support and shielding around the slit-slat collimator. Lead slats, spaced with Rohacell foam, were mounted in an assembly with 3 mm pitch.We have performed preliminary characterization with point sources and acquired micro hot- and cold-rod phantoms and a Deluxe Jaszczak phantom. The projections have been reconstructed using an MLEM algorithm and show good resolution.Comparisons indicate that SS is more sensitive than PB and FB for the same resolution for smaller-diameter objects. The advantage of SS over PB and FB increases as the desired resolution improves. SS can also be used in configurations that yield projections that have non-isotropic resolution; it is possible for SS to achieve transverse resolutions that are unreachable by PB, since PB does not magnify, and by FB, since its magnification factor for small objects is much smaller than that of SS. Experimental results show that the resolution of the reconstructed phantoms is consistent with theoretical expectations.
Metzler
Scott D
SD
Department of Radiology at The University of Pennsylvania, Philadelphia, PA 19104 USA.
Accorsi
Roberto
R
Ayan
Ahmet S
AS
Jaszczak
Ronald J
RJ
J Nucl Med. 1984 Sep;25(9):1013-8
6332182
Phys Med Biol. 2009 Mar 21;54(6):1469-82
19218734
IEEE Trans Med Imaging. 1982;1(1):63-8
18238259
J Nucl Med. 2006 Nov;47(11):1884-90
17079823
J Nucl Med. 1974 Feb;15(2):59-64
4810590
IEEE Trans Nucl Sci. 2009 Jan 1;56(3):694-703
20204152
Med Phys. 2005 Jul;32(7):2236-44
16121578
IEEE Trans Med Imaging. 2005 Mar;24(3):361-70
15754986
IEEE Trans Med Imaging. 2008 May;27(5):709-22
18450543
Phys Med Biol. 2008 Feb 21;53(4):953-66
18263951
J Nucl Med. 2005 Nov;46(11):1872-80
16269602
IEEE Trans Med Imaging. 1988;7(4):291-7
18230481