Radiation dose and image quality in K-edge subtraction computed tomography of lung in vivo.

K-edge subtraction computed tomography (KES-CT) allows simultaneous imaging of both structural features and regional distribution of contrast elements inside an organ. Using this technique, regional lung ventilation and blood volume distributions can be measured experimentally in vivo. In order for this imaging technology to be applicable in humans, it is crucial to minimize exposure to ionizing radiation with little compromise in image quality. The goal of this study was to assess the changes in signal-to-noise ratio (SNR) of KES-CT lung images as a function of radiation dose. The experiments were performed in anesthetized and ventilated rabbits using inhaled xenon gas in O2 at two concentrations: 20% and 70%. Radiation dose, defined as air kerma (Ka), was measured free-in-air and in a 16 cm polymethyl methacrylate phantom with a cylindrical ionization chamber. The dose free-in-air was varied from 2.7 mGy to 8.0 Gy. SNR in the images of xenon in air spaces was above the Rose criterion (SNR > 5) when Ka was over 400 mGy with 20% xenon, and over 40 mGy with 70% xenon. Although in human thorax attenuation is higher, based on these findings it is estimated that, by optimizing the imaging sequence and reconstruction algorithms, the radiation dose could be further reduced to clinically acceptable levels.

Imaging lobular breast carcinoma: comparison of synchrotron radiation DEI-CT technique with clinical CT, mammography and histology.

Different modalities for imaging cancer-bearing breast tissue samples are described and compared. The images include clinical mammograms and computed tomography (CT) images, CT images with partly coherent synchrotron radiation (SR), and CT and radiography images taken with SR using the diffraction enhanced imaging (DEI) method. The images are evaluated by a radiologist and compared with histopathological examination of the samples. Two cases of lobular carcinoma are studied in detail. The indications of cancer are very weak or invisible in the conventional images, but the morphological changes due to invasion of cancer become pronounced in the images taken by the DEI method. The strands penetrating adipose tissue are seen clearly in the DEI-CT images, and the histopathology confirms that some strands contain the so-called 'Indian file' formations of cancer cells. The radiation dose is carefully measured for each of the imaging modalities. The mean glandular dose (MGD) for 50% glandular breast tissue is about 1 mGy in conventional mammography and less than 0.25 mGy in projection DEI, while in the clinical CT imaging the MGD is very high, about 45 mGy. The entrance dose of 95 mGy in DEI-CT imaging gives rise to an MGD of 40 mGy, but the dose may be reduced by an order of magnitude, because the contrast is very large in most images.

Small-angle x-ray scattering studies of human breast tissue samples.

Small-angle x-ray scattering (SAXS) patterns are recorded from thin breast tissue samples containing healthy and cancerous regions. The SAXS patterns are compared with histo-pathological observations. The information available from SAXS is reviewed, and a model for scattering from collagen is presented. Scattering patterns of collagen at regions far from the tumours are essentially different from those at tumours. The axial period of collagen fibrils is 65.0 +/- 0.1 nm in healthy regions, and 0.3 nm larger in cancer-invaded regions. The average intensity of scattering from cancerous regions is an order of magnitude higher than the intensity from healthy regions. This is interpreted to arise from an increase of the specific surface area of the scatterers, which is due to a disruption of the molecular and supra-molecular structures in cancerous regions and invasion of new types of cells. The differences of the SAXS patterns are large and distinctive enough to suggest that these phenomena may be utilized in mammography.

SU-E-J-54: Bone Detection in MR Images and Absorbed Dose in a Material Behind Bones in Radiotherapy.

PURPOSE: To determine whether bones could be localized accurately by using MR images only in radiotherapy treatment planning. Furthermore, to measure absorbed dose in a material behind different parts of the bone, and to evaluate dose calculation error in a pseudo-CT image by assuming a single electron density for the bones. METHODS: A dedicated phantom was constructed using fresh deer bones and gelatine. The accuracy of the bone edge location and the bone diameter in MR images were evaluated by comparing those in the images with the actual measures. The absorbed dose behind the bones was measured by a matrix detector at 6 and 15 MV. Thedose calculation error in the bulk density pseudo-CT image was quantified by comparing the calculation results with those obtained in a standard CT image by superposition and Monte Carlo algorithms (TPSs: Xio 4.60 and Monaco 3.00, Elekta CMS Software). RESULTS: The examination of bone position revealed that the bones can be localized within a 1-mm-pixel-size in the MR images. The measured dose behind less than 2.5-cm-thick femur indicated that the absorbed dose behind the middle part of the bone is approximately one percentage unit (6 MV: 1.3%, 15 MV: 0.9%) smallerthan that of the physically narrower bone edge. The calculations illustrated that the bulk density pseudo-CT image used causes errors up to nearly 2% to the dose behind the middle part, but also, the edge of the femur. CONCLUSIONS: This research ascertains that the bone localization is not a restrictive issue for radiotherapy treatment planning by using MR imageonly. The work indicates also that the decrease in absorbed dose is not necessarily dependent on the diameter of the bone. Future research shouldinvestigate the generation of more complex pseudo-CT images and the dosecalculations by using these. Supported by Elekta.

USAXS and SAXS from cancer-bearing breast tissue samples.

USAXS and SAXS patterns from cancer-bearing human breast tissue samples were recorded at beamline ID02 of the ESRF using a Bonse-Hart camera and a pinhole camera. The samples were classified as being ductal carcinoma, grade II, and ductal carcinoma in situ, partly invasive. The samples included areas of healthy collagen, invaded collagen, necrotic ducts with calcifications, and adipose tissue. The scattering patterns were analyzed in different ways to separate the scattering contribution and the direct beam from the observed rocking curve (RC) of the analyzer. It was found that USAXS from all tissues was weak, and the effects on the analyzer RC were observed only in the low-intensity tails of the patterns. The intrinsic RC was convolved with different model functions for the impulse response of the sample, and the best fit with experiment was obtained by the Pearson VII function. Significantly different distributions for the Pearson exponent m were obtained in benign and malignant regions of the samples. For a comparison with analyzer-based imaging (ABI) or diffraction enhanced imaging (DEI) a "long-slit" integration of the patterns was performed, and this emphasized the scattering contribution in the tails of the rocking curve.