Novel sensing and image reconstruction approaches for molecular X-ray emission tomography (#4343)
S. Tzoumas1, D. Vernekohl1, L. Xing1
1 Stanford University School of Medicine, Department of Radiation Oncology, Palo Alto, California, United States of America
X-ray luminescence computed tomography (XLCT) and X-ray fluorescence computed tomography (XFCT) are emerging high-resolution molecular imaging technologies that use X-rays as an excitation source to stimulate the secondary emission of photons from nanoparticles, which are used as molecular agents. XLCT images X-ray-excitable nanophosphors which, upon excitation, emit near-infrared (NIR) photons. The diffuse photons exiting the sample are subsequently detected using an EM-CCD camera. Conversely, in XFCT, the X-ray excitation of nanoparticles with high atomic number stimulates a secondary X-ray emission, also termed X-ray fluorescence. The secondary X-ray emission is detected using energy resolving detectors for the separation of the X-ray fluorescence from the X-ray scattered signal. XFCT and XLCT offer a substantial enhancement in molecular imaging sensitivity as compared to conventional X-ray imaging and offer higher resolution than commonly used molecular imaging modalities. Nevertheless, both methods suffer from high image acquisition times, since tomographic imaging is typically achieved by scanning a pencil-beam of X-rays across the imaged object at discrete translation and rotation steps, similar to the first-generation X-ray transmission CT. We present recent progress in the development of X-ray emission tomography through the employment of novel sensing and image reconstruction approaches that reduce significantly the image acquisition time and improve image quality and sensitivity.
Keywords: X-ray, molecular imaging, XFCT, XLCT
Selective plane x-ray induced luminescence (#4352)
P. J. La Riviere1
1 University of Chicago, Department of Radiology, Chicago, Illinois, United States of America
X-ray induced luminescence (XIL) is a hybrid X-ray/optical imaging modality that employs nanophosphors that luminescence in response to X-ray irradiation. It has traditionally been explored either in a first-generation tomographic geometry, where individual lines are irradiated and photons collected with a non-imaging geometry or in a full-illumination geometry, where the whole object is illuminated and imaging detectors capture the diffuse surface radiance. The first case can achieve high resolution but is relatively slow. The second case is essentially equivalent to diffuse optical tomography and suffers from the same ill-posedness of that modality as well as a need to acquire such images from many different angles. We consider a compromise approach called selective plane XIL (SPXIL) in which collimated x-rays illuminate a single plane through the object. The surface radiance is captured by a camera orthogonal to the illumination plane. This substantially improves the ill-posed reconstruction problem and allows reconstruction of nanoparticle distributions at depth by solving 2D linear equations that reduce to deconvolution in the case of homogeneous optical properties. We will discuss imaging models, experimental results, and considerations of depth, resolution, and sensitivity.
Keywords: x-ray luminescence, radiotherapy
Cherenkov imaging for real-time verification and monitoring of external beam radiotherapy (#4349)
P. Bruza1, J. M. Andreozzi1, D. J. Gladstone2, 3, L. A. Jarvis2, 3, J. Rottmann4, B. W. Pogue1, 2
1 Dartmouth College, Thayer School of Engineering, Hanover, New Hampshire, United States of America
Cherenkov radiation, resulting from megavoltage radiation beam delivery during external beam radiotherapy, has been shown to be detectable from patient’s skin and from water phantoms. Cherenkov imaging was enabled by developing a gated, intensified detection system, and by implementing on-line X-ray noise filtering algorithms. Captured real-time videos of visible Cherenkov light emission from patient’s skin can provide information of the beam shape and local 2D surface dose. An overlay of detected Cherenkov emission on patient’s 3D surface mesh can be used to monitor intra- and interfraction stability and conformity of radiation beams. A pre-treatment verification using Cherenkov emission was demonstrated on a range of radiotherapy devices. By imaging a side of a water tank, a projected 2D view of the beam can be captured at video frame rates, providing information of depth-dose distribution and cross-beam profiles. When combined with cine portal imaging, a dynamic 3D dose distribution in water phantom can be reconstructed for IMRT or VMAT plan verification. This imaging may serve for routine visualization of treatment delivery, as well as for verification of highly conformal treatment plans prior to application to the patients.
Keywords: Cherenkov imaging, Radiotherapy, Dosimetry, VMAT, LINAC, Dose Volume, Image Intensifier
Broadband X-ray Fluorescence Emission Tomography (#4350)
J. George2, E. M. Zannoni3, M. Wilson3, 1, L. - J. Meng2, 3
1 Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, United Kingdom of Great Britain and Northern Ireland
In this presentation, we will discuss our recent effort in developing a broadband X-ray fluorescence emission tomography (XFET) imaging system for guiding and monitoring the delivery of nanoparticle-mediated X-ray induced photodynamic therapy (X-PDT) and for visualizing metal (ions), such as platinum, gadolinium and hafnium, artificially introduced in living organism as contrast or therapeutic agents.
The basic approach that we employed is essentially a stimulated emission tomography, in which we use SPECT-inspired collimation apertures coupled to high-resolution X-ray imaging spectrometers. Our latest prototype XFCT system utilizes a newly developed ultrahigh spectral resolution CdTe detector for fluorescence X-rays of energy 5 keV~100 keV. In this study, we will focus on the feasibility of using this system to monitor the delivery of nanoparticle-mediated X-ray induced photodynamic therapy (X-PDT), but it would readily benefit a wide variety of other imaging applications as well.
X-ray induced PDT (X-PDT), a collimated external X-ray beam is used to irradiate the target region filled with nanoparticles to induce local therapeutic effect through photosensitization, thermal ablation or other effects. During the X-PDT delivery process, the interactions between the externally delivered X-rays and metal atoms encapsulated in PDT agents could generate fluorescence X-rays. Detecting these X-ray signals could allow us to build up a precise 3D distribution of the specific metal in the target area and help to confirm the exact delivery of the therapeutic agents. this work, we focus on PDT agents containing high-Z metal elements, such as Au, Hf, La, and potentially Pt and Gd. The choice of high-Z elements would greatly increase the selective absorption of the excitation X-rays. These elements would also emit higher-energy fluorescence X-rays (68.8 keV for Au K-a), 43 keV for Gd K-a, 33.4 keV for La-K-a, and 55.8 keV for Hf K-a) that could penetrate a substantial thickness in tissue, which makes it possible for using XFET imaging to monitor the therapeutic delivery in deep tissue.
In this presentation, we will experimentally evaluate both spectral and imaging performance of multiple CdTe detector modules installed around the Xradia Bio MicroCT (MicroXCT-400) as a partial-ring broadband XFET system. We will carry out detailed studies to access spectroscopy capability of the detector for detecting and identifying XF photons, as well as the tomographic imaging performance of an experimentally simulated full-ring XFET system based on the HEXITEC detector modules.
Keywords: XFCT, X-ray induced and nano-particle mediated therapy