The construction of computer tomographic phantoms and their application in radiology and radiation protection

Abstract

In order to assess human organ doses for risk estimates under natural and man made radiation exposure conditions, human phantoms have to be used. As an improvement to the mathematical anthropomorphic phantoms, a new family of phantoms is proposed, constructed from computer tomographic (CT) data. A technique is developed which allows any physical phantom to be converted into computer files to be used for several applications. The new human phantoms present advantages towards the location and shape of the organs, in particular the hard bone and bone marrow. The CT phantoms were used to construct three dimensional images of high resolution; some examples are given and their potential is discussed. The use of CT phantoms is also demonstrated to assess accurately the proportion of bone marrow in the skeleton. Finally, the use of CT phantoms for Monte Carlo (MC) calculations of doses resulting from various photon exposures in radiology and radiation protection is discussed.

Development of a Japanese Adult Female Voxel Phantom

“…However, soft tissues cannot be segmented by a single grey value threshold, because there are no significant differences between densities of most soft tissues. Therefore, image processing techniques [2][3][4]13,14,18,22) are used to segment soft tissues. After segmentations, region-specific identification numbers are assigned to voxels belonging to each organ region in order to identify the segmented regions.…”

“…The mass fractions of hard bone and bone marrow in voxels of the bone tissue were quantified using the previous segmentation techniques. [2][3][4]13,14,18,22) The mass of bone marrow of JF was adjusted to the average 21) of Japanese adult female. Thus, voxels with grey values below 800 were regarded as bone marrow only, voxels with grey values between 800 and 2040 were regarded as a mixture of bone marrow and hard bone, and voxels with grey values higher than 2040 were regarded as hard bone only.…”

“…The organ masses of these phantoms were calculated by multiplying the volume of each organ composed of voxel aggregates by each organ density. [2][3][4]6,18) There are small differences (<5%) between the masses of brain, lower large intestine, skin, and stomach of JF and Japanese averages. On the other hand, most organs of JF are smaller than those of Japanese adult female by more 10%.…”

“…[2][3][4][5][6][7] The first voxel phantoms (BABY and CHILD) for a radiation protection purpose were developed at Gesellschaft für Strahlen und Umweltforschung (GSF). 2,3) Golem 4) and NORMAN 5) were computational phantoms of Caucasian adult male based on the CT and MRI images, respectively. Donna, Helga, and Irene were derived from the CT images of Caucasian adult female.…”

Patient‐specific CT dosimetry calculation: a feasibility study

“…Tomographic phantoms developed from actual patient data provide a more detailed and realistic representation of the human anatomy. Zankl et al ( 30 ) published the first pediatric tomographic computational phantoms derived from CT scans of an infant and a 7‐year‐old child. Organ dose normalized to entrance air kerma for head and chest axial CT scans were calculated.…”