Original ArticleSegmental and global left ventricular function assessment using gated SPECT with a semiconductor Cadmium Zinc Telluride (CZT) camera: Phantom study and clinical validation vs cardiac magnetic resonance
Introduction
Over the last decade, advances in microelectronics and improvements in crystal growth have led to the increased use of Cadmium Zinc Telluride (CZT) materials in nuclear medicine. These new materials are capable of using direct photon conversion and provide high image quality.1 Other attractive features include increased sensitivity, high energy, high spatial resolution, and the ability to be used in compact systems. This novel generation of detectors has led to new solid-state camera designs that overcome the limitations of conventional Anger systems.2,3 Commercially available CZT systems have improved sensitivity and spatial resolution compared with conventional Anger cameras.4
Myocardial perfusion imaging is a widely accepted method for the management of patients with known or suspected coronary artery disease.5,6 Procedures that use ionizing radiation should be performed in accordance with the As Low As Reasonably Achievable (ALARA) concept. A major aim in nuclear cardiology is to reduce both patient radiation exposure7 and imaging time without reducing image quality. This favors the rapid development of new ultrafast cameras in daily clinical routines.8, 9, 10 CZT camera technology enables a significant reduction in both radiation exposure and acquisition time without loss of image quality.11
The measurement of the thickness and brightness of thin structures is limited by the spatial resolution of conventional gamma cameras. The partial volume effect results in an underestimation of activity concentration for small objects,12 i.e., when the object size is smaller than approximately twice the full-width half-maximum (FWHM) of the point spread function. A change in object size, as observed during myocardial contraction, results in changes in the apparent count density and is identified by a systolic increase in brightness. This method based on count density is widely used for assessing regional myocardial function with gated Single-Photon Emission Computed Tomography (SPECT), but the exact quantification of the wall thickening remains limited.13
An underestimation of myocardial wall thickening using CZT SPECT compared to magnetic resonance imaging has been recently reported.14 However, it remains unclear whether the improved spatial resolution provided by CZT SPECT significantly impacts the assessment of systolic count increase.
The aim of this study was to evaluate the impact of a new CZT camera on the assessment of both the regional wall thickening using the count increase method and the global left ventricular (LV) function.
Section snippets
Phantom Study
A phantom study was performed to investigate the relationship between counts and object size under various conditions. The phantom consisted of two eccentric polyvinyl chloride cylinders which simulated a myocardial wall with variable thickness. These cylinders were filled with a saline solution of Tc-99m (148 MBq/L) to simulate the same range of clinical activity. Two different shapes were designed: hypertrophic phantom (cavity diameter 50 mm) and dilated phantom (cavity diameter 80 mm), which
Phantom Study
The effective spatial resolution, assessed as the FWHM using a Tc-99m linear source, was greater with the CZT camera (FWHM = 6 mm) than with the Anger system (FWHM = 14 mm). Although the radioactive concentration was homogeneous within all parts of the phantom, the relative counts measured using both the CZT and Anger cameras were significantly influenced by the partial volume effect.
As shown in Figure 2, there was a significant linear correlation (R2 > 0.99) between the measured relative
Discussion
In this study, the evaluation of the global LV function by CZT camera yielded similar EDV, ESV, and LVEF results compared to CMR. In both the phantom and patients, the increase in spatial resolution provided by the CZT camera had a negative impact on the assessment of myocardial wall thickening, especially in hypertrophic conditions.
In a similar phantom study using a conventional Anger camera, Fukuchi et al18 showed that the relative count increase was correlated to object sizes for thicknesses
Conclusion
Compared to the Anger camera, the CZT camera provided accurate measurements of global LV function and improved myocardial wall thickening in patients with a normal or thinned ventricular wall. However, the increased spatial resolution may lead to an underestimation of regional myocardial wall thickening under hypertrophic conditions. WM analysis was not influenced by motion magnitude and may be a better tool for assessing segmental LV function in daily practice. Further studies are needed to
New Knowledge Gained
CZT camera users should be aware that segmental myocardial function assessment using WM is not influenced by the motion magnitude, unlike wall thickening that is significantly influenced by true systolic thickening with reference to cardiac MR.
Regional wall thickening evaluated by the count increase method is underestimated in hypertrophic segments, as a consequence of an improved spatial resolution.
Acknowledgments
We are grateful to Dr Sylvie Petit, MD, the technologist team at Lille and Caen, and Sebastien Hapdey, PhD, for their advice and technical assistance.
Disclosures
None.
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