to maintain the contrast to noise ratio cnr the noise
The variation in noise and contrast to noise ratio are displayed in . The blue line is the baseline generated by taking the average of noise over a week. The baseline for CNR and noise was set to 34.5 and 64.5, respectively. The accepted deviation was set to 10% for both CNR and noise, based on the Varian linac study() and PIPSpro manual. The green area is within acceptable parameters range; yellow area indicates caution level, and pink area indicates rejection areas, respectively. It can be noted that the noise and CNR lies in the acceptable range over the period four months.
image noise, signal to noise ratio and contrast to noise ratio
The QC-3 phantom can be used to perform the following tests: relative modulation transfer function (RMTF), spatial resolution, signal to noise ratio, and contrast to noise ratio (CNR). The use of QC-3 phantom to determine the quality assurance of the electric portal imaging device (EPID) using the software PIPSpro, which provides the frequencies at 50%, 40% and 30% (f50, f40 and f30) of the maximum RMTF, has been extensively studied in literature.(,) We have used the software to study the consistency of noise and CNR in the MVCT images acquired using TomoTherapy.
Quantitative image quality was determined by measuring signal intensity (HU), IN, signal to noise ratio (SNR) and contrast to noise ratio (CNR) using established criteria , at the left ventricle and LMA on the axial images using a Vitrea work station (Vital Images, version 5.2). Then equal size regions of interest (ROI = 30 mm 3 ) were taken in the contrast filled left ventricle and left ventricular wall. IN was calculated from the standard deviation of Hounsfield density values (HU) within the ROI in the left ventricle. SNR was defined as the ratio of mean signal intensity (HU) divided by IN. CNR was defined as the difference between the mean density (HU) of the left ventricle and left ventricular wall divided by IN. ,,, An ROI was then placed in the LMA and perivascular tissue adjacent to the LMA to determine SNR and CNR of the LMA , and .