Advances in pinhole and multi-pinhole collimators for single photon emission computed tomography imaging

Abstract

The collimator in single photon emission computed tomography (SPECT), is an important part of the imaging chain. One of the most important collimators that used in research, preclinical study, small animal, and organ imaging is the pinhole collimator. Pinhole collimator can improve the tradeoff between sensitivity and resolution in comparison with conventional parallel-hole collimator and facilities diagnosis. However, a major problem with pinhole collimator is a small field of view (FOV). Multi-pinhole collimator has been investigated in order to increase the sensitivity and FOV with a preserved spatial resolution. The geometry of pinhole and multi-pinhole collimators is a critical factor in the image quality and plays a key role in SPECT imaging. The issue of the material and geometry for pinhole and multi-pinhole collimators have been a controversial and much disputed subject within the field of SPECT imaging. On the other hand, recent developments in collimator optimization have heightened the need for appropriate reconstruction algorithms for pinhole SPECT imaging. Therefore, iterative reconstruction algorithms were introduced to minimize the undesirable effect on image quality. Current researches have focused on geometry and configuration of pinhole and multi-pinhole collimation rather than reconstruction algorithm. The lofthole and multi-lofthole collimator are samples of novel designs. The purpose of this paper is to provide a review on recent researches in the pinhole and multi-pinhole collimators for SPECT imaging.

Keywords: Image quality; multi-pinhole collimator; pinhole collimator; reconstruction algorithm; single photon emission computed tomography.

Figure 1

The images of ^99mTc-sestamibi from thyroide at 15 min in a patient with hyperparathyroidism acquired with (a) pinhole and (b) parallel-hole collimators

Figure 2

Two types of the pinhole collimators that routinely used in pinhole single photon emission computed tomography imaging: (a) Knife-edge collimator and (b) channel-edge pinhole collimator

Figure 3

The whole body scan images of ^99mTc-hydroxymethylene diphosphonate from a mouse were acquired with a pinhole collimator and reconstructed by (a) the filtered back projection method for single-orbit data and (b) three-dimensional ordered subsets expectation maximization method for two-orbit data

Figure 4

Schematic of (a) a pinhole collimator and (b) a lofthole collimator with a circular aperture and a rectangular entrance/exit opening. This type of collimator creates the rectangular projection on the detector

Figure 5

Projections from (a) a multi-pinhole collimator that do not fully coverage the detector, (b) multiplexing effect in a multi-pinhole collimator, and (c) projections created from a multi lofthole collimator without the multiplexing effect

Figure 6

A spheric object is imaged by (a) a pinhole collimator; a circular projection was created, (b) a skew slit collimator; an elliptical projection was created. A small cone angle in the axial direction could reduce the data insufficiency artifacts, (c) a multipinhole collimator, and (d) a multi skew slit collimator provide a desire transaxial resolution, detector area usage, and minimum multiplexing effect