The pinhole: gateway to ultra-high-resolution three-dimensional radionuclide imaging

Abstract

Today the majority of clinical molecular imaging procedures are carried out with single-photon emitters and gamma cameras, in planar mode and single-photon emission computed tomography (SPECT) mode. Thanks to the development of advanced multi-pinhole collimation technologies, SPECT imaging of small experimental animals is rapidly gaining in popularity. Whereas resolutions in routine clinical SPECT are typically larger than 1 cm (corresponding to >1,000 microl), it has recently proved possible to obtain spatial resolutions of about 0.35 mm ( approximately 0.04 microl) in the mouse. Meanwhile, SPECT systems that promise an even better performance are under construction. The new systems are able to monitor functions in even smaller structures of the mouse than was possible with dedicated small animal positron emission tomography ( approximately 1 mm resolution, corresponding to 1 microl). This paper provides a brief history of image formation with pinholes and explains the principles of pinhole imaging and pinhole tomography and the basics of modern image reconstruction methods required for such systems. Some recently introduced ultra-high-resolution small animal SPECT instruments are discussed and new avenues for improving system performance are explored. This may lead to many completely new biomedical applications. We also demonstrate that clinical SPECT systems with focussing pinhole gamma cameras will be able to produce images with a resolution that may become superior to that of PET for major clinical applications. A design study of a cardiac pinhole SPECT system indicates that the heart can be imaged an order of magnitude faster or with much more detail than is possible with currently used parallel-hole SPECT (e.g. 3-4 mm instead of approximately 8 mm system resolution).

Will high-resolution/high-sensitivity SPECT ensure that PET is not the only survivor in nuclear medicine during the next decade?

“…Pinhole SPECT was primarily studied in the context of small animal imaging [8][9]. In the beginning, a single pinhole mounted on a commercial Anger camera was used [8].…”

“…In the beginning, a single pinhole mounted on a commercial Anger camera was used [8]. Systems with multiple pinhole with or without the multiplexing of the projections were quickly developed and finally non rotating systems with a large number of small pinholes came onto the market [9]. Such systems combined high resolution, high sensitivity and collection of the data needed for tomographic reconstruction, without the need to rotate the detectors.…”

“…Such systems combined high resolution, high sensitivity and collection of the data needed for tomographic reconstruction, without the need to rotate the detectors. This meant that dynamic studies became as easy in SPECT as they were in PET, and with an even better spatial resolution [9].…”

“…These VOI could be large enough [9] to allow exploration of the brain, the heart, the parathyroid, the thyroid, and some bone regions, such as the ankle, cervical spine, knee, shoulder and wrist, where high resolution and sensitivity are needed. These stationary systems would also allow, to the greater benefit of the patient, the use of the tracers now available and give radiochemists the opportunity to pursue research on both single-photon and positron emitting tracers.…”

Quantification of GABAA receptors in the rat brain with [123I]Iomazenil SPECT from factor analysis-denoised images

“…Labeled with 123 I or 125 I, it has been used as a tracer in human and non-human single-photon emission computed tomography (SPECT). SPECT in small animal research has gained popularity during the past few years as significant progress has been made in the field of small animal imaging instrumentation that has most notably resulted in improvement of its major drawback, limited spatial resolution [6,9,10]. Despite this technical development, several factors degrade SPECT images and limit the potential for quantitative estimations.…”