# Gamma Camera Spatial Resolution

The laboratory report presents the different data gathered and results discussion in the Gamma Camera Spatial Resolution experiment. The experiment measures the Intrinsic and Extrinsic Resolution of the Gamma Camera. It incorporates the use of the Hander Equation in order to accurately describe intrinsic resolution. The system and collimator resolution is also compared at differing source-to-collimator distances. The collimator resolution, in turn is compared to the Anger equation. Methodology Intrinsic Spatial Resolution • Set the bay phantom at a space of 5 hole diameters from the source as shown in Figure 1.

• Determine the source activity, count rate, matrix size, zoom, pixel size, and total count at a definite scan time as indicated through the manual or as gathered through the experiment. Spatial Resolution vs. Hander Equation • Use the customs SIEMENS software to determine the statistical quantities µ and ? over a drawn ROI in the smallest resolvable bar width. Extrinsic Spatial Resolution • Place the LEHR collimator on the detector and position a line source under the collimator at varying distances of 0, 2, 5, 10, 15, 20 and 25 cm. The detector should follow the specifications as described in Figure 2.

• Determine the source activity, count rate, matrix size, zoom, pixel size, and total count at a definite scan time as indicated through the manual or as gathered through the experiment. • Use the custom SIEMENS software to measure Rs. Record the FHWM value. • Set 0 = S (1) (approximate) for the experiment. Results and Discussion The following results were gathered through performing the experiment as stated in the methodology: Spatial Resolution vs. Hander Equation The ellipse ROI has an average of 883. 79 counts per pixel with a standard deviation of 56. 94 as observed in the figure..

It is observed that the use of the Hander equation produces more accurate results, which is in fact close to 35, only deviating by about 0. 006. According to Hander, the scatter and aperture corrections should be applied to the model, along with the use of statistical mean and variance, in order to produce a more accurate result (Hander, 2000). The small difference is applicable for acceptance testing; however, as the pixel size increases, the difference in the accuracy of the said method increases. For this experiment, the Hander equation produced a difference of 0. 01. Graphing the System Resolution vs.

the Distance of the Collimator and the Source, the following graph is obtained. Although a cubic function represents the graph better than a linear one in terms of correlation, the linear model is also a good approximation of the model. Thus the model should be taken as linear, with a slight deviation to the left of the graph. The graph shows that as the source-collimator distance increases, the system resolution proportionally increases. It can be observed that the pixel size has been reduced, thus, a finer quality of the image is achieved. It is also seen that the scan time vis-a-vis total count has decreased.

This means that the total counts per minute has decreased in the extrinsic spatial resolution as compared to the intrinsic spatial resolution. The use of big pixels produces a pixilated image while the use of small pixels produce a finer, higher quality image. A good image can be produced at 10 pixels/FWHM. Graphing the Collimator Resolution vs. the Distance of the Collimator and the Source, the following graph is obtained. It shows a very good linear relationship, with a correlation of 1. Thus, the collimator resolution is proportional to the source-collimator distance.

It can be observed that there is a large %error for the Anger Collimator Resolution and the derived Collimator Resolution. It can also be inferred that as the distance of the collimator from the source increases, the difference decreases at a fast, decreasing rate. Since Ri is constant, it can also be inferred that Rs varies the difference in the Rc. It is thus conclusive that Rs increases in accuracy as the distance from the source increases. References Hander, T. , et al. An improved method for rapid objective measurement of gamma camera resolution. Texas: Department of Radiology, 2000. Print.

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