Evaluasi Nilai Noise Sebelum Dan Sesudah Kalibrasi Sebagai Salah Satu Wujud Kinerja Pesawat CT-Scan

Abstract

The noise has to be measured daily because it directly degrades image quality, which in
turn it is dificult to define between normal and pathological tissues on a-CT image. This
research’s aim was performed to examine noise differences between before and after
calibrating of the CT-scanner system, and also to study the chance of noise deviated values day-
by-day during 20 days of the two different periods of measurement.
A callibrated head water phantom was scanned before and after equipment callibrations,
using the head scanning parameter, and device measurement at ROI 228.2 mm2 to obtain the
noise data. Descriptive statistics was employed to present related information, and the T-test
paired-sample was the statistical tool to test the null hypothese (Ho) with level of significance
(α) 0.05.
The results showed most of noise values between before and after equipment calibrations
fall arround the base line or within two standard deviation (2SD). In before callibration of the
noise, the base line noise value is 4.76 HU whereas the upper limit and the lower limmit of the
noise values are 5.34 HU and 4.18 HU (respectively) with a-1.16 HU difference. In after
callibration of the noise, the base line noise value is 4.35 HU whereas the upper limit and the
lower limmit of the noise values are 5.29 HU and 3.41 HU with a-1.87 HU difference. However,
there are two out of fourty noise values (± 5%) that fall outside of the 2SD limmit if a number
falls outside of 2SD from the base line in the same direction (i.e., all high or all low) more than
four days in a row, it is a shift that could be due to a machine malfunction and should be
investigated before the outer control limit is exceeded. Statistical analyses with paired- sample
T-test showed p-value (0.005) < 0.05. By this meaning that, the noise between before and after
CT-Scanner callibrations are different in their values additonally most of the noise values after
callibration seem to be low compared with that of the values before callibrations.
Keywords: CT scan, evaluation, noise.