Mannudeep Kalra MD, PRESENTER: Nothing to Disclose

Abstract: HTML Purpose: Automatic tube current modulation (ATCM) is a technique that modulates CT tube current to maintain pre-selected image quality(noise index). Lower noise index (NI) means better image quality but higher radiation dose. This study was performed to determine the impact of patient weight on image noise and diagnostic acceptability of abdominal-pelvis CT examinations obtained with various NI using ATCM. Methods and Materials: 120 patients (age=19-87 years, mean age=61 years, M:F=67:83) underwent abdominal-pelvis CT with 16-slice multidetector row CT scanner (GE Lightspeed 4.X) using ATCM technique at NI of 10 (n=20), 10.5 (n=21), 11 (n=25), 11.5 (n=34) and 12 (n=20). The remaining scanning parameters ncluded: 0.5s gantry rotation time, 140 kVp, 0.938:1 pitch, 1.25x16 detector collimation, 18.75mm table speed/rotation, 5mm reconstructed slice thickness. Subject weight was recorded and CTDIw values were noted from the CT console. Two subspecialty radiologists evaluated the studies for abnormalities, presence of artifacts and graded the image quality for noise, diagnostic acceptability at diaphragmatic aspect of liver, porta hepatis, right kidney hilum, iliac crest and acetabulum using 5-point scale (1=unacceptable; 3=acceptable; 5=excellent). Statistical analysis was performed to determine whether patient weight impacts image noise and diagnostic acceptability of studies acquired with different NI and whether it should be used for selecting image quality using ATCM. Results: 101 lesions detected in study cohort comprised of 28 liver masses, 14 renal calculi, 14 adrenal masses, 12 uterine adnexal masses, 11 bowel masses, 8 gall stones, 7 pancreatic masses and 3 patients with splenic leisions. In 19 subjects, CT did not reveal any abnormality. At NI of 11 and above, increased beam hardening artifacts were noted at superior aspect of liver and increased image noise was seen, more often in subjects with weight less than 80 kg. In such subjects, although no significant statistical difference was noted, lower NI of 10 resulted in more satisfactory image noise and diagnostic acceptability than higher NI (p>0.05). Paradoxically, in subjects above 80 kg, greater NI(up to 12) were found to be acceptable. Conclusion: ATCM technique for abdominal-pelvic CT warrants lower NI and greater radiation exposure to yield a satisfactory image noise and diagnostic acceptability (with less artifacts) in low weight subjects. Conversely, higher NI(with less radiation exposure) can yield acceptable image quality in subjects weighing more than 80 kg.     (T.L.T. is an employee of GE Medical Systems.) Questions about this event email: mannudeep_k_kalra@yahoo.com

Kalra MD, M, Multidetector CT Scanning of Abdomen and Pelvis: A Study for Optimization of Automatic Tube Current Modulation Technique in 120 Subjects.  Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL. http://archive.rsna.org/2003/3107471.html