SPECT

What Is SPECT?

        SPECT is short for single photon emission computed tomography. As its name suggests (single photon emission) gamma rays are the sources of the information rather than X-ray emission in the conventional CT scan.

Image Acquisition

        Nuclear medicine images can be acquired in digital format using a SPECT scanner. The distribution of radionudide in the patient’s body corresponds to the analog image. An analog image is one that has a continuous distribution of density representing the continuous distribution of radionuclide amassed in a particular organ. The gamma ray counts coming from the patient’s body are digitized and stored in the computer in an array or image matrix. Typical matrix sizes used in SPECT imaging are 256x256, 128x128, 128x64 or 64x64. The third dimension in the array corresponds to the number of transaxial, coronal or sagittal slices used to represent the organ being imaged.

 Data filtering

        Once the data has been transformed to the frequency domain, it is then filtered in order to smooth out the statistical noise. There are many different filters available to filter the data and they all have slightly different characteristics. For instance, some will smooth very heavily so that there are not any sharp edges, and hence will degrade the final image resolution other filters will maintain a high resolution while only smoothing slightly .

Introduction

        Emission Computed Tomography is a technique where by multi cross sectional images of tissue function can be produced , thus removing the effect of overlying and underlying activity. The technique of ECT is generally considered as two separate modalities. SINGLE PHOTON Emission Computed Tomography involves the use single gamma ray emitted per nuclear disintegration. Positron Emission Tomography makes use of radio isotopes such as gallium-68, when two gamma rays each of 511KeV, are emitted simultaneously where a positron from a nuclear disintegration annihilates in tissue. SPECT, the acronym of Single Photon Emission Computed Tomography is a nuclear medicine technique that uses radiopharmaceuticals, a rotating camera and a computer to produce images which allow us to visualize functional information about a patient’s specific organ or body system.

Positron Emission Tomography (Pet)

        The distribution of activity in slices of organs can be obtained in a more accurate way using PET. In the simplest PET camera two modified sophisticated cameras called Anger cameras are placed on opposite sides of the patient. This increases the collection angle and reduces the collection times which are the limitations of SPECT .In PET, radiopharmaceuticals are labeled with positron emitting isotopes. A positron combines rather quickly with an electron. As a result the two gamma quanta are emitted almost in opposite directions .In PET scanners, rings of gamma ray of gamma ray detectors surrounding the patient are used. Each detector interacts electronically with the other detectors in the field of view. When a photon arrives within a short time frame, it is clear that a pair of quanta was generated and that these were created somewhere along the path between the detectors. Conventional PET tomography makes use of standard filtered back projection techniques used in computed tomography and SPECT.

Abstract

        SPECT, the acronym for Single Photon Emission Computed Tomography, is a nuclear medicine imaging modality, giving information about a patient’s specific organ or body system. The patient is injected with a radiopharmaceutical, which will emit Gamma rays.

Conclusion

        It is reasonable to speculate about a constant by perhaps a slower rate of increase of clinical applications of SPECT. It is safe to conclude that SPECT has reached the stage where it will be a valuable and also an unavoidable asset to the medical world.