Radiotracers for SPECT imaging: current scenario and future prospects

Abstract

Summary. Single photon emission computed tomography (SPECT) has been the cornerstone of nuclear medicine and today it is widely used to detect molecular changes in cardiovascular, neurological and oncological diseases. While SPECT has been available since the 1980s, advances in instrumentation hardware, software and the availability of new radiotracers that are creating a revival in SPECT imaging are reviewed in this paper.The biggest change in the last decade has been the fusion of CT with SPECT, which has improved attenuation correction and image quality. Advances in collimator design, replacement of sodium iodide crystals in the detectors with cadmium zinc telluride (CZT) detectors as well as advances in software and reconstruction algorithms have all helped to retain SPECT as a much needed and used technology.Today, a wide spectrum of radiotracers is available for use in cardiovascular, neurology and oncology applications. The development of several radiotracers for neurological disorders is briefly described in this review, including [123 I]FP-CIT (DaTSCAN™) available for Parkinson's disease. In cardiology, while technetium-99m labeled tetrofosmin and technetium-99m labeled sestamibi have been well known for myocardial perfusion imaging, we describe a recently completed multicenter clinical study on the use of [ 123 I]mIBG (AdreView™) for imaging in chronic heart failure patients. For oncology, while bone scanning has been prevalent, newer radiotracers that target cancer mechanisms are being developed. Technetium-99m labeled RGD peptides have been reported in the literature that can be used for imaging angiogenesis, while technetium-99m labeled duramycin has been used to image apoptosis.While PET/CT is considered to be the more advanced technology particularly for oncology applications, SPECT continues to be the modality of choice and the workhorse in many hospitals and nuclear medicine centers. The cost of SPECT instruments also makes them more attractive in developing countries where the cost of a scan is still prohibitive for many patients.

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“…This is easier to achieve if the radionuclide can be attached with the least possible modifications to the structure of the parent compound. For example, small molecular weight compounds are often radiolabelled with ‘organic’ radionuclides such as 18 F, 11 C or radioiodine [17,18] to give radiopharmaceuticals with similar or even identical chemical structures. Alternatively, molecules can be radiolabelled using radiometals which require a chelator, which is a specific type of metal-binding molecule that provides stable radiometal conjugates [19].…”

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“…5, 6). If fully developed, this approach could increase the proportion of successful ictal SPECTs [35,[37][38][39][40][41][42][43][44][45].…”