To investigate how the radiation dose level affects the detection of microcalcifications (MCs) in cone beam breast CT (CBCT), simulated MCs were embedded in simulated breast tissue and imaged with an experimental CBCT system. The system employs a 30 x 40 cm2 a-Si/CsI based flat panel detector with a pixel size of 194 microns. Three 5 x 5 clusters of simulated calcifications (212-224, 250-280, and 300-355 μm) were embedded in a stack of 11 cm diameter lunch meat and positioned at the center of each slice of lunch meat. 300 projection images over 360 degrees were acquired in the non-binning mode at various dose levels (4.2, 6, 12, 18, and 24 mGy) three times, and were reconstructed with the Feldkamp algorithm. After that, 767 x 767 x 9 volume data were extracted from the fifteen reconstructed images for each size group, resulting in 45 CBCT MC phantom images. An observer experiment was performed by counting the number of visible MCs for each MC phantom image. The phantom images were displayed on a review workstation with a 1600 x 1200 CRT monitor and reviewed by six readers independently. The order of the images was randomized for each reader. The ratios of the visible MCs were averaged over all readers and plotted as a function of the dose level. The CNR was calculated for each MC size and each doe level as well. The results showed that the performance of the reconstructed images acquired with 4.2 mGy was similar to the images acquired with 6 mGy, and the images acquired with 18 mGy performed similarly to those acquired with 24 mGy.
Purpose: To compare two detector systems - one based on the charge-coupled device (CCD) and image amplifier, the
other based on a-Si/CsI flat panel, for cone beam computed-tomography (CT) imaging of small animals.
A high resolution, high framing rate detector system for the cone beam CT imaging of small animals was developed. The
system consists of a 2048×3072×12 bit CCD optically coupled to an image amplifier and an x-ray phosphor screen. The
CCD has an intrinsic pixel size of 12 μm but the effective pixel size can be adjusted through the magnification
adjustment of the optical coupling systems. The system is used in conjunction with an x-ray source and a rotating stage
for holding and rotating the scanned object in the cone beam CT imaging experiments. The advantages of the system
include but are not limited to the ability to adjust the effective pixel size and to achieve extremely high spatial resolution
and temporal resolution. However, the need to use optical coupling compromises the detective quanta efficiency (DQE)
of the system. In this paper, the imaging characteristics of the system were presented and compared with those of an a-
Si/CsI flat-panel detector system.