GATED SPECT :GATED SPECT BY: ALBERTO ARIAS


OBJECTIVES :OBJECTIVES Learn what Gated SECT is Understand how Gated SPECT works Learn some of the differences between GSPECT and standard SPECT


DEFINITION :DEFINITION Gated SPECT is an acquisition technique where the patients ECG (electrocardiogram gating) is used to guide the acquisition This procedure is capable of producing excellent tomographic images of the myocardium reflective of regional perfusion in addition to LV functional parameters, which taken together, provide enhanced physiologic assessment of the heart


DEFINITION (cont.) :DEFINITION (cont.) In other words SPECT can be used to obtain quantitative information about myocardial perfusion, thickness, and contractility of the myocardium during various parts of the cardiac cycle It also allows the calculation of left ventricular ejection fraction, stroke volume, and cardiac output


HOW IT WORKS :HOW IT WORKS The acquisition computer is used to define the number of frames (bin) in which the RR interval (inter-beat interval) are to be divided, usually 8 frames but 16 frames can also be utilized The patient ECG is connected to the computer, and the RR intervals over 30-60 sec are collected and usually displayed graphically as a histogram


HOW IT WORKS (cont.) :HOW IT WORKS (cont.) A 10-20% window is selected around the mean RR interval, which means that all data from cardiac cycles within this window will be accepted The data from RR intervals outside the limits of the window will be not be accepted and thus be rejected


HOW IT WORKS (cont.) :HOW IT WORKS (cont.) When the acquisition is started, the computer waits for the first R waves to check if the RR interval is within the established limits. If the RR interval is within the defined limits, the data is accepted, if not the data is rejected The data from the first 1/8 of the cardiac cycle are stored in frame 1) the data from second 1/8 is stored in bin 2 and it continues like this for the rest of the cardiac cycle


HOW IT WORKS (cont.) :HOW IT WORKS (cont.) When the predefined acquisition time or angle is reached, the camera moves 3 degrees to the next angle, waits for the R signal, receives the signal and starts the collecting the information This procedure repeated over 180 degrees


COMPARISON BETWEEN REGULAR SPECT and GSPECT :COMPARISON BETWEEN REGULAR SPECT and GSPECT Standard SPECT In a regular SPECT study , for example a 180 degree-60 steps-30 sec / step setup, one 30 sec projection image is obtained from each step So just 60 image projections are done


COMPARISON BETWEEN REGULAR SPECT and GSPECT :COMPARISON BETWEEN REGULAR SPECT and GSPECT GSPECT 8 projection images are obtained at each step Each image represents what the heart looked like in that 1/8 of a fraction of the cardiac cycle Each image is obtained over about just 4 sec A complete gated SPECT acquisition thus consists of 8 files each representing a fraction (eighth) of the cardiac cycle, each file is processed with a backprojection algorithm to generate 8 tomographic sets of data These data sets are then rearranged to a dynamic study


REQUIREMENTS for a GSPECT STUDY :REQUIREMENTS for a GSPECT STUDY Acquisition software Software for reconstruction Lots of disk space A reasonable fast computer For the quality of gated SPECT study to be good an ECG signal with well defined positive R wave and regular cardiac rhythm are required Premature beats with short or long RR intervals, will fall outside the defined window and will prolong the acquisition


CONCLUSION :CONCLUSION Gated SPECT is an acquisition technique where the patients ECG is used to guide the acquisition It is used for studying the heart It takes a picture for every eighth of the cardiac cycle


QUESTIONS :QUESTIONS What is GSPECT? Gated SPECT is an acquisition technique where the patients ECG is used to guide the acquisition 2) In how many frames are the RR intervals divided? Usually 8 frames 3) Is it done over a 180 degrees or 360 degrees? 180 degrees


QUESTIONS (cont.) :QUESTIONS (cont.) 4) How long does it take for each image to be obtained? 4 secs 5) What windows are usually used? 10% or 20%


REFERENCES :REFERENCES http://www.medwave.cl/congresos/mednuclear2004/1/1.act www.wikipedia.org www.csmc.edu/5849.html