Evaluation of arterial phase images with 90vp in multiphase abdominal CT scan

Abstract

Introduction: CT scan of abdomen is usually performed in 120-140 kVp and such high ranges of kilovoltage in all phases will increases the radiation dose many fold. The purpose of the study was to qualitatively and quantitatively assess image quality with low kVp in arterial phase of examination of multiphasic abdominal CT study.

Methods: A prospective cross-sectional study was done in 206 participants of age 18 to 88 years who were undergoing multiphase CT studies of the abdomen in Neusoft 16 detector MDCT. After performing non contrast scan, arterial phase study of limited region of abdomen (diaphragm to infrarenal margins) was obtained with 90 kVp. The portovenous phase scan with standard protocol was obtained (120kVp). All other scanning parameters were kept same for two phases. Images were rated on 5 point scale (1-worst, 2-Suboptimal, 3-adequate,4-very good,5-excellent) based on visualization of boundaries, anatomical details of the organs and visualization of noise and artifact by two radiologists. Patient weight, abdominal circumference (AC), height and BMI were recorded and correlated with the image quality score. Statistical analysis was done with Wilcoxon’s signed ranks test k test and descriptive analysis.

Results: Overall the image quality of portovenous phase was significantly better (p<0.005) than low kVp arterial phase. Image quality score correlated best with abdominal circumference in standard dose technique (r=0.54) and patient weight in reduced dose technique (r=0.44). Arterial phase scanning had acceptable image quality score for patient weight of <60 kg, AC <80cm and BMI<25 kg/m2. The CTDIvol was 7.71 with reduced kVp protocol and 20.02 with standard resulting significant reduction in radiation dose of about 61%

Conclusions: The image quality of arterial phase images with 90kVp tube potential is acceptable in thin and average built patients. Hence reduction in radiation dose is possible if arterial phase scanning is done with reduced kVp except in patients with large anthropometric parameters.