Effect of Slice Thickness Variation on Spatial Resolution of CT-Scan Device Images at the Bali Mandara Hospital Radiology Installation

Aims: Slice thickness variation analysis on spatial resolution on CT-scan images by determining CNR and SNR values, by making ROI on object and background images. ROI size of objects and backgrounds can be observed with several criteria based on the provisions of the ACR program, so that optimization of CT-Scan image quality can be achieved.

Place and Duration of Study: The Radiology Installation in Bali Mandara Hospital, between 23 March to 20 May 2022.

Methodology: Data collection begins with preparing the equipment used, namely CT-Scan, head holder, phantom, and computer. After that, the head holder is placed in the middle of the gantry and then the phantom is placed with the guidance of the laser beam (alignment system). Set the axial beam on the vertical line of section 1 and then set the coronal beam on the horizontal line of section 2. After that, setting the type of examination using the adult head protocol and setting the scan parameters to 80 kV, 100 mAs, and slice thicknesses 1, 2, 3, 4, 6, and 8 mm. After the preparation is done then the next exposure to the phantom. Then the research data in the form of phantom images will be seen as a whole to program on the computer monitor. Measurements were made 5 times for each slice thickness. Next is to analyze the CNR of digital phantom image data on a computer. So that it can be determined object ROI, background ROI, object mean, background mean, and standard deviation of the background.

Results: The results showed that the thicker the Slice Thickness, the higher the CNR and SNR values. The highest CNR value occurred in air medium (13.70) and the lowest occurred in Nylon (0.86). Likewise, the highest SNR value occurred in air medium (13.84) and the lowest in Nylon (0.99). The highest CNR and SNR values ​​occurred in air medium and the lowest occurred in Nylon.

Conclusion: Slice Thickness variations affect the spatial resolution of CT-Scan images as indicated by the CNR and SNR values however, the CNR and SNR values ​​are still above 1.0 for adult head examination and above 0.7 for children's head examination. So that the quality of CT-Scan images at Bali Mandara Hospital is still very good.