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Methods, Apparatus, and Computer Readable Mediums for Performing Perfusion Studies
UIRF #: 04019; Inventors: Dr. G. Wang, Dr. Y. Wei, and Dr. J. Hsieh
Background:
Perfusion studies in the human body have rapidly become an effective method in the diagnosis and treatment of
such ailments as strokes, cancer, and heart diseases. One such method, CT perfusion, involves the injection of a
bolus constraint into a blood vessel within proximity of a targeted organ, and then quantifying the resulting data
as it travels into the organ. For example, in CT head profusion imaging collect such parameters as mean transit
time (MTT), cerebral blood volume (CBV), and cerebral blood flow (CBF). However, the greatest limitation in
CT perfusion imaging is the patient risk of exposure to high dosages of X-rays during scanning. Furthermore,
efforts to reduce the dosages have decreased the signal to noise ratios and in turn resulted in poor image quality.
Researchers at the University of Iowa have achieved alternative scanning methods that successfully reduce the
dosage level without reducing image quality.
Technological Description:
The widely accepted method of X-ray dose reduction in CT perfusion is to reduce the X-ray tube current. The
drawback is that this increases the resulting noise level of the measured projection data. Research at the
University of Iowa has led to the development of a method that uses a controllable apparatus to achieve a
fractional scanning protocol and prediction algorithms that address incomplete projection data issues. The
Partial Scan Protocols (PSP) works by maintaining high milliamperage setting while only collecting a fraction
of the typical 360-degree dataset. The missing portion of the data set is predicted, based on a priori knowledge
that as the bolus medium propagates through the body its concentration within a given organ decreases at a
predictable rate gradually over time. This is important because the differences between one fractional scan
from another is trivial. The missing portion is then estimated from the known projection of the same geometry
using a Projection Interpolation Algorithm. However, there are instances where the interpolation process can
introduce projection errors or bias. To overcome this, the PSP projection images can also be reconstructed
using an Image Prediction Algorithm (IPA) which uses a full scan image as its baseline, and then extrapolates
data based on this image to predict the missing portions from the PSP fractional scan. Both methods produce
high resolution perfusion images that are reconstructed at a fraction of the nominal radiation dose.
Technological Advantages:
HIGH SIGNAL TO NOISE RATIO: Typically reducing the milliamperage level reduces the X-ray dosage.
This in turn increases the data noise and degrades the perfusion image. By reducing the fractional scan, the
milliamperage is allowed to remain at high levels without lowering the signal to noise ratio.
LOW X-RAY DOSAGE: As with all CT modalities there is a risk of cancer due to high levels of radiation
exposure. The technology is an example of methods being implemented to reduce this risk.
Patent:
Methods, Apparatus, and Computer Readable Mediums for Performing Perfusion Studies;
www.google.com/patents/US6934353
Publications:
Hsieh J, Wei YC, Wang G: Fractional Scan Algorithms for Low-Dose CT Perfusion. Medical Physics
31:1254-1257, 2004
This and other relevant papers can be downloaded at: http://www.imaging.sbes.vt.edu/publications