CT Imaging

X-ray CT solutions for high spatial and temporal resolution!

Dose increases with the fourth power of resolution and SAI protocols often necessitate multiple scans on a single animal. The combination of these two factors emphasizes the necessity of careful dose monitoring.

Identifying the sensitivity of specific organs to radiation is difficult. At present, adherence to the ALARA “As Low As Reasonably Achievable” principle seems to be the only acceptable strategy. One reasonable proposal is a limitation to typically 100 mSv per examination. As pre-clinical imaging moves forward it is essential to make dose assessment an integral part of every protocol, since animals deserve the same care and protection as humans.



In collaboration with the Institute of Medical Physics (www.imp.uni-erlangen.de) and the QRM GmbH (www.qrm.de) we designed a set of phantoms based on guidelines for clinical CT. The phantoms were scaled down from the diameter of an average human trunk (32 cm) to that of a fat mouse or lean rat (32 mm). Parameters measured were CT values, noise, homogeneity, contrast scale factor, spatial resolution and scan time. Noise was defined as the standard deviation for a 10 mm ROI in a 32 mm water phantom. Spatial resolution was evaluated by both visual inspection and by modulation transfer function (MTF). The assessment also included dose measurements for each acquisition. The phantoms were tested on four different commercial micro-CT models with two protocols: high speed and high image quality.



The proposed phantoms allow micro-CT scanners to be evaluated in an analogous manner to clinical CT. Particular attention was given to the measurement of noise, spatial resolution and dose assessment. Quantitative evaluation on different scanners yielded significant differences with respect to dose efficiency as indicated by the figures of merit.

CT images of phantoms with 32 mm diameter for noise (a), spatial resolution (b,c), slice sensitivity profile (d), low-contrast detectability (e) and contrast scale factor measurements (f). (Phantom by our partner QRM, Möhrendorf, Germany, www.qrm.de).