Accurate tissue area measurements with considerably reduced radiation dose achieved by patient-specific CT scan parameters.

ABSTRACT

A low-dose technique was compared with a standard diagnostic technique for measuring areas of adipose and muscle tissue and CT numbers for muscles in a body composition application. The low-dose technique was intended to keep the expected deviation in the measured area of adipose and muscle tissue to <1% of the total tissue area. The largest diameter of the patient determined the parameters for the low-dose technique. 17 patients - chosen to cover a wide range of diameters (31-47 cm) for both abdomen and thighs - were examined using both techniques. Tissue areas were compared, as were CT numbers for muscle tissue. Image noise was quantified by standard deviation measurements. The area deviation was <1%, except in the smallest subjects, in whom it was <2%. The integral radiation dose of the low-dose technique was reduced to 2-3% for diameters of 31-35 cm and to 7.5-50% for diameters of 36-47 cm as compared with the integral dose by the standard diagnostic technique. The CT numbers of muscle tissue remained unchanged with reduced radiation dose. Image noise was on average 20.9 HU (Hounsfield units) for subjects with diameters of 31-35 cm and 11.2 HU for subjects with diameters in the range of 36-47 cm. In conclusion, for body composition studies with CT, scan protocols can be adjusted so that the integral dose is lowered to 2-60% of the standard diagnostic technique at our centre without adversely altering area measurements of adipose and muscle tissue and without altering CT numbers of muscle tissue.