Physics

Dose Tracking

Our group has been developing dose tracking systems (DTS) that enable precise patient dose distribution measurements for dynamic procedures including those with ROI and MAF techniques. DTS, now a product of Toshiba, won first prize as the Best New Radiology Software for 2014 in a contest sponsored by the well-known trade group AuntMinnie.com.

Dose Tracking System display with the previous version of a patient graphic showing the skin dose distribution in real time during a cardiac catheterization procedure being performed on a 68 year old female patient.

https://www.youtube.com/watch?v=nTwB10l0avA

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High Resolution Imaging and Detectors

During endovascular interventions it is necessary to have the best possible real-time image guidance especially at critical stages of the intervention but only over the region of interest of the pathology being treated. For this reason we have been developing high resolution dynamic detectors that far exceed the capabilities of current imagers. Prototypes of these Micro-Angiographic Fluoroscopy (MAF) detector systems have received laudatory acceptance by clinicians. It is expected that soon these new capabilities will become the new standard of care first in neurovascular interventions and later in pediatrics, cardiology and other applications

Movie 1: https://www.youtube.com/watch?v=fY-OpedS1H0

Movie 2: https://www.youtube.com/watch?v=dT6-tReQCcg

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  • Microangiographic fluoroscope shows coiling of an aneurysm 
  • Fluoroscopic snapshot using a microangiographic fluoroscope shows individual coils and accurate catheter positioning with respect to the coil mass

Region of Interest Imaging

As image guided interventional procedures continue to replace invasive surgical procedures and longer patient x-ray exposure times are required, there is an urgent need to reduce patient dose without jeopardizing outcomes. We have pioneered ROI techniques to achieve this goal by preserving the best image within the ROI while reducing dose peripheral to the ROI. With recent digital imaging developments we have been able to further improve real-time ROI imaging using differential temporal filtering to reduce noise especially outside the ROI and we have even combined ROI dose reduction and high resolution MAF imaging for biplane image guidance.

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Metrics for Image and Detector Quality Evaluation

When developing new imaging systems, objective evaluation criteria are essential. We are pioneers in generalizing existing linear systems metrics by considering whole systems rather than just detectors resulting in generalized system metrics of GMTF and GDQE. We have also developed a practical gauge of noise in the Instrumentation Noise Equivalent Exposure (INEE) and a new practical way of measuring system MTF just from the noise response. A new family of metrics, Relative Object Detectability (ROD) with a comprehensive set of generalized G-RODs, is our most recent contribution to enable practical comparisons of different systems for specific imaging tasks.

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  • Measured modulation transfer function for: a 300 μm thick CsI(Tl) phosphor, calculated K-fluorescence re-absorption and analytical fit for the CsI MTF

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  • Measured normalized noise power spectra for a high resolution detector at various exposures.

 

Scatter Reduction

An age-old problem in radiographic imaging is contrast and signal to noise ratio (SNR) reduction due to Compton scattering, the most probable interaction of medical x-rays with soft tissue. We pioneered a scanning beam scatter reduction method for rapid sequence imaging and applied ROI attenuation as well; however, the most common method for scatter reduction, the convenient-to-install grid, creates grid-line structured artifacts that appear as structured noise even if it oscillates during an exposure. These structures become more significant for higher resolution detectors and so we have been developing methods to divide out the grid noise patterns.

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  • Example of grid artifacts in a x-ray detector (left) a) and correction
Micro-Computed Tomography

Micro–Computed Tomography is based on Cone Beam Computed Tomography which is a imaging modality used in hospital CT scans or angiography units, but on a small scale with increased resolution. Theses systems are used for non destructive 3D microscopy. We build our own system where we employed our own x-ray detectors. The system at TSVRC has resolution of 8 microns and uses a control software and reconstruction developed by our staff. The system has been used for endovascular devices integrity study, bone structure, tumor imaging, etc. 

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Micro-CT sections of explanted aneurysms treated with 2 types of Asymmetric Stent taken at 3 positions, as indicated in the schematic. Brighter dots are the nitinol struts of the stents, white arrows indicate the soft tissue, and dotted arrows indicate the holder.

X-ray Fluoroscopy

X-ray fluoroscopy is an medical imaging modality used to obtain real-time moving images. The image acquisition rate is high to allow real time visualization of internal organ motion or two guide an intervention where an interventionalist observes the motion and the position of a device in a patient. Due to extensive use the x-ray exposure is low to avoid dose and could lead to noisy images. Our group has been involved in novel approaches to improve the image quality while decreasing the dose. This involved development of new hardware, imagers and software, some of which are implemented on clinical units.

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Alignment of the Asymmetric Vascular  Stent with regard to the aneurysm neck using Fluoroscopy. The white arrows indicate the four platinum markers. On left column we show the images acquired using a high resolution detector (MAF) and on the right column those acquired with the standard x-ray imager. In the top row the stent is un-deployed, in the bottom row images the stent is deployed

Cone Beam Computed Tomography

Cone beam computed tomography (CBCT) is a medical imaging technique similar to computed tomography. The X-rays are divergent, forming a cone incident on a detector. The entire system is placed on a C-arm which can rotate around the patient. CBCT has become routine procedure in treatment planning and diagnosis cardiovascular disease. Our group uses such imaging modality on a regular basis. We have focused mostly in implementation of region of interest detectors which could be used to give high resolution volumes in a particular area. We also work on new reconstruction algorithms and acquisition to optimize the image quality while decreasing the dose delivered to the patient.

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Cone Beam CT of an Elastase Aneurysm Model, Bone rendering is blue and arteries are in red.

Angiography

Angiography is a medical imaging technique used to visualize the blood vessels lumen. This is done by injecting a radio-opaque contrast agent, such as Iodine, into the blood vessel via a catheter and imaging using X-ray imaging. This is a diagnosis technique which uses larger  x-ray exposures for a very short period of time. We have been working with the Toshiba engineers to improve the quality of the images y improving hardware, imaging devices and software. In addition novel analysis methods were developed to estimate physiological blood flow based only on angiography.

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B. Digital subtraction angiography (DSA) images acquired with the standard x-ray image intensifier demonstrate no residual filling of the aneurysm. 

C. Microangiographic fluoroscope Digital subtraction angiography (DSA) of a coiled aneurysm

Dose Measurements and Quality Assurance

X-ray based medical imaging is a complex process which involves x-ray production, interaction of the radiation with mater, radiation detection, image formation and post processing. To reduce effects of ionization on live tissue while maintaining high image quality, medical physicists dedicate a lot of effort to optimize such x-ray systems. A part of the research in our group is focused on the development of standard radiographic phantoms and analysis methods. We developed standard phantoms equivalent to human anatomy which were used successfully to improve imaging and detectors.

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Fluoroscopic evaluation of various contrast features using different views through an head equivalent views

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  • Radiographic evaluation of various contrast metrics using different views through an head equivalent views

 

Research Focus

Stephen Rudin, Ph.D., Daniel Bedanrek Ph.D., and Ciprian Ionita Ph.D. head the imaging physics group at the Toshiba Stroke and Vascular Research Center.

Most recently, this group developed a micro-angiographic fluoroscopy (MAF) system that can show detail at the site of neurological intervention two to three times more clearly than imaging equipment now in use. The team has now translated the system to the clinical suites and is working to determine the full range of clinical benefits offered by the MAF’s unique features.

Researchers at the center are also currently working to adapt new CMOS flat panel technology to the MAF system to enable both improved resolution and larger fields of view. When integrated commercially, the system will be inherently more flexible than any equipment currently on the market and should set a new standard of patient care.

The group also is a focus of the nationally accredited UB Medical Physics Graduate Program of which Dr. Rudin is the Director. More information can be found at the indicated link on this page.

http://www.smbs.buffalo.edu/medphysics/index.shtml