Shuai Leng PhD, Presenter: Nothing to Disclose

Kristin D. Zhao MA, Abstract Co-Author: Research support, Socorex Isba SA

Sanjeev Kakar MD, Abstract Co-Author: Nothing to Disclose

Lifeng Yu PhD, Abstract Co-Author: Nothing to Disclose

Cynthia H. McCollough PhD, Abstract Co-Author: Research grant, Siemens AG

To investigate and compare two skin dose estimation methods for a 4D CT technique that used to assess dynamic wrist instability.

Two methods were investigated to assess skin dose in the 4DCT scans: 1) a previously developed size specific skin dose estimation method based upon volume CT dose index (CTDIvol) and 2) physical measurement on an anthropomorphic phantom. For method 1), skin dose was estimated using an expoential relationship between skin dose and patient size at a given CTDIvol: skin dose = 2.31 x exp(-0.016x(lateral+AP)) x CTDIvol, in which lateral and anterior-posterior (AP) width was measured in centimeter and CTDIvol was recorded from the scanner console. For method 2), an anthropomorphic wrist phantom, 7 cm and 4.5 cm measured in the lateral and AP dimensions, was scanned on a 128 slice dual source CT scanner (Definition Flash, Siemens Healthcare, Forchheim, Germany). A 4DCT scan, the same as that used in patient study to assess dynamic wrist instability, was conducted with canning parameters of 120 kVp, 100 mAs per rotation, 0.28 second rotation and 128x0.6 mm beam collimation. There was no table translation during the total 2 sec data acquisition time (one cycle of wrist motion), similar as perfusion technique. A 0.6cc ion chamber was placed at the surface of the wrist to measure skin doses. Measurements were conducted at two different locations: top and lateral side of the wrist. And measurements were repeated three times at each location. Peak and averaged skin dose was obtained.

The recorded CTDIvol was 36.4 mGy and estimated skin dose was 69.3 mGy based on the equation in method 1). Using method 2), peak skin dose was measured as 81.4 mGy at the top of the wrist phantom, and averaged skin dose of 76.1 mGy. The difference of averaged doses estimated using the two methods was 9%.

Skin dose from the 4DCT imaging techqiue was well below any potential skin effect (threshold of 2000 mGy). The size specific dose estimation method provided a close estimation compared with the physical phantom measurement. Skin dose estimated from this study could be applied to a wide range of patients as wrist size difference is small among patients.

With the estimated skin dose, 4DCT imaging technique can be used as an effective tool for detecting dynamic wrist injuries without concerning potential skin effect.

Leng, S, Zhao, K, Kakar, S, Yu, L, McCollough, C, Skin Dose Estimation in a 4D CT Imaging Technique That Used to Assess Dynamic Wrist Instability.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034500.html