Greg Clement, Ph.D., Core PI
Cycle II 2010-1015
The field of image guided therapy (IGT) has progressed dramatically in recent years both in the number of IGT sites as well as the range of procedures available. CT- and MR-guided procedures were previously confined primarily to brain, spine, and joint surgery but now are increasingly being utilized for the thorax, abdomen, and pelvis. Meanwhile, changes in health-care practice continue the trend from open surgery toward minimally invasive or non-invasive therapeutic techniques. Although this progress in clinical IGT offers the prospective of more robust, safe, and rapid interventions, it also presents enormous technical challenges for medical imaging. To safely treat smaller volumes and more geometrically complex pathology, we must improve spatial and temporal imaging resolution. Also, a need exists to process images in novel ways to provide accurate and valuable information for treatments.
The Imaging Core is presented with the central task of resolving technical issues that impede the breadth and volume of IGT procedures due to the inability to acquire and display accurate treatment information. Imaging challenges center on motion-induced degradation of image spatial resolution and low image contrast in many anatomic regions. Motion artifacts such as those caused by respiratory or cardiovascular motion lead to lower spatial resolution imaging in those regions. Conversely, motion correction techniques are generally temporally inefficient due to physiologically-synchronized scanning. While efficiency compromises may be acceptable for diagnostic imaging, the critical decision-making required during intervention requires timely and robust answers. In addition, resolution of relatively small changes in image contrast, such as those due to tissue heating or to the uptake of oxygen by tissue, is currently difficult due to motion-artifact masking. The major tasks we aim to address in the next phase of the work of the Imaging Core, which all center on moving anatomy are: (1) MR temperature mapping in moving organs, (2) tracked high-resolution MR imaging about (or surrounding) catheters and endoscopes, and (3) ultrasound mapping of tissue perfusion.
The Imaging Core’s overall goals are to substantially improve existing IGT applications and to enable new applications. Imaging in the presence of moving tissue is perhaps the greatest challenge to nearly all areas of IGT and is, thus, the Core’s central concentration. Resolution of relatively small changes in image contrast, such as those due to tissue heating, blood perfusion, or the uptake of oxygen by tissue, is highly difficult due to motion-artifact masking. We will seek to overcome these challenges in the proposed work of the Imaging Core. The proposed set of projects will meet the following objectives:
Specific Aim 1: Temperature Mapping in Moving Organs. To develop an approach for monitoring temperature changes in moving organs during ablation procedures with sufficient temporal resolution to resolve breathing motion (2 frames per second or more), with sufficient tem-perature resolution to generate useful temperature maps (2 degrees C or less), and with 3D coverage (3 slices or more).
Specific Aim 2: Tracked High-resolution MR imaging of Catheters and Endoscopes. We will employ MRI imaging with prospective motion compensation to perform high-resolution MRI imaging of physiologically-moving tissues in the abdomen and heart. The basis for this work is the use of motion-tracking devices to provide a measure of the motion (translation, rotation) of the tissue of interest. Motional information will be used to synchronize acquisition and to correct the imaging parameters in each pass of the imaging sequence for motion that has occurred between successive passes. Using these techniques, we expect to obtain high-resolution images in clinically acceptable (e.g. 15 second breath-hold) imaging times. We will focus on T1- and T2-weighted contrast MRI pulse sequences, thus providing the central tools required for intra-procedural visualization of soft tissues surrounding a catheter or endoscope, as it is being navigated within the heart or the abdomen.
Specific Aim 3: Ultrasound Mapping of Tissue Perfusion for IGT. We will investigate the use of 3D contrast-enhanced US perfusion mapping for real-time targeting and guidance in IGT. Specifically, we will seek (1) To obtain real-time volumetric perfusion maps in a rabbit tumor model for targeting, and (2) To develop automated algorithms that both display and quantify volumetric perfusion data before and after ablative therapy as a means of monitoring and maybe even controlling the treatment. We will benchmark the potential of the contrast-enhanced US perfusion method against existing MR-guidance methods.
- Jing Y., Tao M., Clement G.T. Evaluation of a Wave-vector-frequency-domain Method for Nonlinear Wave Propagation. J Acoust Soc Am. 2011 Jan;129(1):32-46. PMID: 21302985.
- Yuan J., Madore B., Panych L.P. Fat-water Selective Excitation in Balanced Steady-state Free Precession using Short Spatial-spectral RF Pulses. J Magn Reson. 2011 Feb;208(2):219-24. PMID: 21134770. PMCID: PMC3034310.
- Hoge W.S., Tan H., Kraft R.A. Robust EPI Nyquist ghost elimination via spatial and temporal encoding. Magn Reson Med. 2010 Dec;64(6):1781-91. PMID: 20665898. PMCID: PMC3038256.
NCIGT Cycle I 2005-2010
A principal goal of the Imaging Core within the National Center for Image-Guided Therapy in Cycle I was to develop freely available libraries of functions to support enhanced imaging in IGT. The Core disseminated a toolbox of enhanced imaging libraries to the broader IGT community and to provide expertise in its use to support IGT applications. They are three separate but compatible libraries containing:
- functions to support real-time data acquisition, reconstruction and scanner control
- functions to support enhanced imaging including the principal parallel imaging methods, temporal sampling methods such as UNFOLD and other fast imaging approaches
- functions to enable 2D RF selective excitation for reduced field-of-view imaging.
In addition to the development of these libraries, the Core has worked to apply them synergistically in a series of IGT applications such as thermal monitoring during focused ultrasound treatments and the tracking of devices during IGT procedures.
Research projects involving the Imaging Core from Cycle I included: