Digital tomosynthesis is a type of limited angle tomography that allows 3D information to be reconstructed
from a set of x-ray projection images taken at various angles using an x-ray tube, a mechanical arm to rotate the tube
about the object, and a digital detector. Tomosynthesis reconstruction requires the precise location of the detector with
respect to each x-ray source, forcing all current clinical tomosynthesis systems to use a physically coupled source and
detector so the geometry is always known and is always the same. This limits the imaging geometries and its large size
is impractical for mobile or field operations. To counter this, we have developed a free form tomosynthesis with a
decoupled, free-moving source and detector that uses a novel optical method for accurate and real-time geometry
calibration to allow for manual, hand-held tomosynthesis and even CT imaging.
We accomplish this by using a camera, attached to the source, to track the motion of the source relative to the
detector. Attached to the detector is an optical pattern and the image captured by the camera is then used to determine
the relative camera/pattern position and orientation by analyzing the pattern distortion and calculating the source
positions for each projection, necessary for 3D reconstruction. This allows for portable imaging in the field and also as
an inexpensive upgrade to existing 2D systems, such as in developing countries, to provide 3D image data. Here we
report the first feasibility demonstrations of free form digital tomosynthesis systems using the method.
Microbeam radiation therapy (MRT) uses an array of high-dose, narrow (~100 μm) beams separated by a
fraction of a millimeter to treat various radio-resistant, deep-seated tumors. MRT has been shown to spare normal tissue
up to 1000 Gy of entrance dose while still being highly tumoricidal. Current methods of tumor localization for our MRT
treatments require MRI and X-ray imaging with subject motion and image registration that contribute to the
measurement error. The purpose of this study is to develop a novel form of imaging to quickly and accurately assist in
high resolution target positioning for MRT treatments using X-ray fluorescence (XRF). The key to this method is using
the microbeam to both treat and image. High Z contrast media is injected into the phantom or blood pool of the subject
prior to imaging. Using a collimated spectrum analyzer, the region of interest is scanned through the MRT beam and the
fluorescence signal is recorded for each slice. The signal can be processed to show vascular differences in the tissue and
isolate tumor regions. Using the radiation therapy source as the imaging source, repositioning and registration errors are
eliminated. A phantom study showed that a spatial resolution of a fraction of microbeam width can be achieved by
precision translation of the mouse stage. Preliminary results from an animal study showed accurate iodine profusion,
confirmed by CT. The proposed image guidance method, using XRF to locate and ablate tumors, can be used as a fast
and accurate MRT treatment planning system.
Micro-beam radiation therapy (MRT) uses parallel planes of high dose narrow (10-100 um in width) radiation beams separated by a fraction of a millimeter to treat cancerous tumors. This experimental therapy method based on synchrotron radiation has been shown to spare normal tissue at up to 1000Gy of entrance dose while still being effective in tumor eradication and extending the lifetime of tumor-bearing small animal models. Motion during the treatment can result in significant movement of micro beam positions resulting in broader beam width and lower peak to valley dose ratio (PVDR), and thus can reduce the effectiveness of the MRT. Recently we have developed the first bench-top image guided MRT system for small animal treatment using a high powered carbon nanotube (CNT) x-ray source array. The CNT field emission x-ray source can be electronically synchronized to an external triggering signal to enable physiologically gated firing of x-ray radiation to minimize motion blurring. Here we report the results of phantom study of respiratory gated MRT. A simulation of mouse breathing was performed using a servo motor. Preliminary results show that without gating the micro beam full width at tenth maximum (FWTM) can increase by 70% and PVDR can decrease up to 50%. But with proper gating, both the beam width and PVDR changes can be negligible. Future experiments will involve irradiation of mouse models and comparing histology stains between the controls and the gated irradiation.
Chest tomosynthesis is an imaging modality that provides 3D sectional information of a patients thoracic cavity
using limited angle x-ray projections. Studies show that tomosynthesis can improve the detection of subtle
lung nodules comparing to conventional radiography at a lower radiation dose than CT. In the conventional
design, the projection images are collected by mechanically moving a single x-ray source to different viewing
angles. We investigated the feasibility of stationary chest tomosynthesis using the distributed CNT x-ray source
array technology, which can generate a scanning x-ray beam without any mechanical motion. A proof-of-concept
system was constructed using a short linear source array and a at panel detector. The performance of the source
including the flux was evaluated in the context of chest imaging. The bench-top system was characterized and
images of a chest phantom were acquired and reconstructed. The preliminary results demonstrate the feasibility
of stationary chest tomosynthesis using the CNT x-ray source array technology.