The efficiency of breast density assessment using interactive intensity thresholding applied to intensity uniformity corrected
T1-weighted MR images is investigated for 20 healthy women who attended the UK multi-centre study of MRI screening for
breast cancer. Mammographic density is estimated on the medial-lateral oblique X-ray mammograms using CUMULUS. MR
density assessment is performed using both high and low-resolution T1-weighted images. The left and the right breast
regions anterior to the pectoral muscle were segmented on these images using active contouring. For each region, intensity
uniformities were corrected using proton density images and a user selected uniformity factor. An interactively selected
threshold is applied to the corrected images to detect fibrogulandular tissue. The breast density is calculated as the ratio of the
classified fibroglandular tissue to the segmented breast volume.
There is no systematic difference, good consistency and a high correlation between the left and the right breast densities
estimated from X-ray mammograms and the high and low-resolution MR images. The correlation is the highest and the
consistency is the best for the low-resolution MR measurements (r=0.976, MeanAbsoluteDifference = 2.12%). Mean breast
densities calculated over the left and the right breasts on high and low-resolution MR images are highly correlated with
mammographic density (r=0.923 and 0.903, respectively) but are approximately 50% lower.
Interactive intensity thresholding of T1-weighted MR images provides an easy, reproducible and reliable way to assess breast
density. High and low-resolution measurements are both highly correlated with the mammographic density but the latter
requires less processing and acquisition time.
Since the discovery of X rays radiotherapy has had the same aim - to deliver a precisely measured dose of radiation to a defined tumour volume with minimal damage to surrounding healthy tissue. Recent developments in radiotherapy such as intensity modulated radiotherapy (IMRT) can generate complex shapes of dose distributions. Until recently it has not been possible to verify that the delivered dose matches the planned dose. However, one often wants to know the real three-dimensional dose distribution. Three-dimensional radiation dosimeters have been developed since the early 1980s. Most chemical formulations involve a radiosensitive species immobilised in space by gelling agent. Magnetic Resonance Imaging (MRI) and optical techniques have been the most successful gel scanning techniques so far. Optical techniques rely on gels changing colour once irradiated. Parallel beam optical tomography has been developed at the University of Surrey since the late 1990s. The apparatus involves light emitting diode light source collimated to a wide (12cm) parallel beam. The beam is attenuated or scattered (depending on the chemical formulation) as it passes through the gel. Focusing optics projects the beam onto a CCD chip. The dosimeter sits on a rotation stage. The tomography scan involves continuously rotating the dosimeter and taking CCD images. Once the dosimeter has been rotated over 180 degrees the images are processed by filtered back projection. The work presented discusses the optics of the apparatus in more detail.