Chapter 4: Cardiac SPECT and PET Instrumentation

INTRODUCTION

The changing needs of cardiologists and patients have led to an unprecedented evolution in nuclear cardiology instrumentation. Modern instrumentation has a wide range of collimation, attenuation correction (AC) options, and many of the newest systems no longer relying on the Anger gamma camera design. Solid-state detector technologies and new aperture designs are commercially available and in widespread use. Hybrid SPECT and PET systems now have transmission imaging options for AC using x-ray CT, radionuclide, or novel fluorescence x-ray sources.

The changes in instrumentation have been driven by revolutionary changes in the delivery of health care. In particular, there has been a shift from office-based nuclear cardiology services to hospital-based imaging. According to MedAxiom, respondents reported a dramatic shift in providers from private practices to integrated practices. In 2008, only 11% of MedAxiom respondents reported being in an integrated group (e.g., integrated into a hospital environment). By 2012, almost 60% of respondents reported practicing within an integrated practice.¹ The integration of cardiovascular imaging into the hospital setting has significantly altered the kinds of instrumentation available to the cardiologist. This access has provided clinicians the capability for routine AC, neuronal imaging, absolute blood flood, sarcoid imaging, amyloid imaging, metabolic imaging (glucose and fatty acid tracers) and other advanced molecular imaging techniques. This chapter will describe the instrumentation that is commonly used in nuclear cardiology and explain some of the important advances in instrumentation that can improve image quality and reduce radiation exposure.

SPECT INSTRUMENTATION

Anger Camera

Hal Anger, with his team at the University of California, Berkeley had worked with the rectilinear scanners and pin-hole camera designs. In 1957, this group changed the design to allow for a uniform magnification and resolution across the field of view with increased system sensitivity. The first "Anger" scintillator camera consisted of a 4-in sodium iodine crystal optically coupled to 7 photomultiplier tubes (PMTs).^2,3

Gamma camera design has evolved significantly since 1957 with improvements in resolution, sensitivity, and energy discrimination, however the conceptual design of the Anger camera is remarkably unchanged. The "Anger" gamma camera consists of (see Fig. 4-1):

• Focusing, multi-hole collimator: The focusing collimator is placed in front of the other camera components. The image is formed by excluding photons not traveling along a particular path, for example, perpendicular to the camera face or holes focusing on a point or line.

• Scintillation crystal: A material that will luminesce with optical photons when excited by ionizing radiation.

• PMT array: Electronics for capturing the photons produced by the scintillator crystal and converting those photons into an electronic pulse.

• Analog-to-digital conversion hardware: A digitization board converts the analog pulse-height information into a position and energy for each photon event.