SPECT(Single Photon Emission Tomography)

[abinayabaskaran]

             SPECT scanner is most rarely known among all.It is actually a  tomographic imaging technique used to create  a three dimensional representation of the distribution of an administered radio pharmaceutical by using gamma rays.

             It is named so as SPECT camera detect only radio nuclides that produce a cascaded emission of single photons.

             The scaning technique has its broad application in the field of  neuro imaging and myocardial perfusion imaging.Because, SPECT permits accurate localisation in 3D space, it can be used to provide information about localised function in internal organs, such as functional cardiac or brain imaging

              SPECT in myocardial perfusion imaging:

                 Myocardial perfusion imaging (MPI) is a form of functional cardiac imaging, used for the diagnosis of ischemic heart disease.

                 The underlying principle is that under conditions of stress, diseased myocardium receives less blood flow than normal myocardium.

                  MPI is one of several types of cardiac stress test.A cardiac specific radiopharmaceutical is administered, e.g., 99mTc-tetrofosmin (Myoview, GE healthcare)

                  Following this, the heart rate is raised to induce myocardial stress, either by exercise or pharmacologically with adenosine, dobutamine, or dipyridamole (aminophylline can be used to reverse the effects of dipyridamole).SPECT imaging performed after stress reveals the distribution of the radiopharmaceutical, and therefore the relative blood flow to the different regions of the myocardium

                 Diagnosis is made by comparing stress images to a further set of images obtained at rest.MPI has been demonstrated to have an overall accuracy of about 83% (sensitivity: 85%; specificity: 72%), and is comparable with (or better than) other non-invasive tests for ischemic heart disease.

                SPECT in functional brain imaging:

                   Usually, the gamma-emitting tracer used in functional brain imaging is Tc-HMPAO (hexamethylpropylene amine oxime). 99mTc is a metastable nuclear isomer that emits gamma rays that can be detected by a gamma camera.

                  Attaching it to HMPAO allows 99mTc to be taken up by brain tissue in a manner proportional to brain blood flow, in turn allowing cerebral blood flow to be assessed with the nuclear gamma camera.Because blood flow in the brain is tightly coupled to local brain metabolism and energy use, the  tracer to assess brain metabolism regionally, in an attempt to diagnose and differentiate the different causal pathologies of dementia

                  Meta-analysis of many reported studies suggests that SPECT with this tracer is about 74% sensitive at diagnosing Alzheimer’s disease vs. 81% sensitivity for clinical exam (cognitive testing, etc.).

                  More recent studies have shown the accuracy of SPECT in Alzheimer’s diagnosis may be as high as 88%. In meta analysis, SPECT was superior to clinical exam and clinical criteria (91% vs. 70%) in being able to differentiate Alzheimer’s disease from vascular dementias

                   SPECT is more widely available, because the radioisotope used is longer-lasting and far less expensive in SPECT, and the gamma scanning equipment is less expensive as well.

                                                                                                                                                                by

                                                                                                                                                            abinaya

[AJISH ALFRED]

good one ! suggest you to write an article on it and showcase it on this site

[abinayabaskaran]

Thank you.will do it soon

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