Advancing Medical Imaging with IDL

by Jon Snyder

Editor's Note: Read more about IDL 5.0 in Beagle Review, in a previous Software Alert column, or in our list of favorite software programs.

Non- and minimally invasive diagnostic techniques are giving physicians improved methods for assessing patient illness and determining optimal treatment plans. Computers powerful enough to process these large data sets are now cost-effective for radiologists, cardiologists, general practitioners, and others using ultrasonic, computed tomography (CT), or magnetic resonance imagery (MRI).

Software application developers now have powerful tools such as Research Systems' Interactive Data Language (IDL) to produce easy-to-use programs tailored for specific medical imaging conditions. The results are greater safety and accuracy in objective and subjective clinical observations as well as increased surgical success.

Ultrasound imaging has always been the safest way to investigate the human body. The cost of ultrasonic imaging is relatively low compared to CT and MR. In combination with other testing, a full assessment of a patient's progress and health can be made reasonably accurately, and without exposing the patient to radiation inherent with X rays and conventional CT scans.

Paritosh Dhawale of Technology Solutions Group, Ltd., has adapted ultrasonic imaging to provide 3-D visualization and quantification of atherosclerosis, a major cause of heart attacks. Dhawale's IDL application, called Ultrasound Quantitative Analysis Software, delivers more accurate estimates than X-ray imaging of the extent of atherosclerotic damage.

To analyze the atherosclerotic buildup, ultrasonic data is collected by a 1.2 mm-diameter transducer that is introduced into the artery and maneuvered to the point of blockage. Initially, the transducer provides a 2-D cross section of the arterial wall. 3-D data is produced by pulling the sensor through the atherosclerotic narrowing. The data is then processed and visualized in IDL, allowing physicians to assess the extent of arterial blockage and help determine whether angioplasty is required. To provide better insight, Dhawale's application simultaneously displays the image in multiple windows for side-by-side comparison.

One reason that intracoronary ultrasound analysis surpasses the accuracy of X-ray analysis is that it doesn't rely on a dye injected into the artery. Depending on the angle of observation, physicians sometimes have difficulty distinguishing arterial plaque from dye in X-ray images. With intracoronary analysis there is no dye to cloud the picture, and data is collected at the point of blockage, resulting in high-resolution, highly reliable images.

Although inserting a catheter into the artery is an invasive procedure, the associated risk is low and the data is gathered as quickly as possible. Cardiologists read collected data, initiate processing, and adjust image characteristics through a graphical user interface (GUI). Most importantly, the GUI makes the system available and useful to users with absolutely no programming experience.

Initially Dhawale was skeptical about using non-workstation platforms for data analysis and graphics. However, after running time tests of the application, Dhawale learned that a "P5 166's benchmarks were better than a standalone Sparc-10, which costs three times as much. Also, I find IDL code in Windows 95 to be stable, and the graphics performance is excellent."

Dhawale's package runs on Power Macintosh, Windows, and Unix computers, and is available in five levels of functionality to meet varying performance needs.

In many life-threatening situations, CT and MR imagery can give doctors a life-saving edge. Abdominal aortic aneurysms are distensions in the aortic artery that usually form near the point where it meets the iliac arteries. The bulge is painful, puts pressure on any nearby organs, and may rupture, which would eventually result in death. For treating such aneurysms, medical physicist Anne Martel of the Queen's Medical Centre in Nottingham, United Kingdom, developed an analysis tool for radiologists and surgeons that makes CT images useful for accurate aneurysm measurements. From such measurements a suitable graft is built to replace or patch the distended aorta.

The old method of analyzing abdominal aortic aneurysms involved selecting oblique slices through CT data and measuring the distance between two or three points on those slices. According to Martel, "This was very time-consuming. Inadequate, if the vessels were tortuous." In her application, the CT data is processed and enhanced with IDL. A general-purpose segmentation tool, implemented through the point-and-click GUI, allows the radiologist and surgeon to isolate the abdominal aorta within the 3-D images. Software-controlled functions like thresholding, region growing, and morphological operations are also performed through the GUI. The bone is masked and maximum intensity projection (MIP) images are created. This allows the doctor to see the aneurysm itself as well as selected bones, blood vessels, and surrounding organs. The physician can visually assess the extent of the aneurysm's effect and devise a plan for effectively reaching and repairing it.

The radiologist defines curved slices through the MIPs to display the entire aorta. Then a line is defined down the calculated center of the aorta and iliac arteries. After this line is established, it is possible to determine the distance between any two points and obtain precise measurements for building the graft. Since the graft is made to fit perfectly, high-risk patients spend less time under anesthesia because the surgeon has an effective strategy for repair. Surgeons benefit by knowing before the patient is on the operating table that the graft will solve the problem.

When Dr. Justin Smith of the First Hill Diagnostic Center in Seattle, Washington, wanted a better, easier way to look at MRI data to determine how far cancer had spread in a body, he found that none of the available methods were sufficient. He turned to Applied Research Technologies of Portland, Oregon, for help. Ken Gindroz, president of Applied Research Technologies; Dr. Smith; and a consultant from Research Systems planned and developed a software application called PRO-MRI. PRO-MRI is a GUI-controlled application built in IDL that applies pattern recognition methods to the high volume of multivariate data generated by MR imaging.

A crucial part of the system was the user interface design. "Most radiologists or bio-imaging scientists don't have the time or background to use currently available statistical application software," Gindroz said. Therefore, access to IDL's large data-set processing power needed to be exceptionally intuitive. Working with the physicians who were going to use the application, analysis options such as the ability to draw regions of interest by hand were incorporated and made easy to implement. To measure the progress of a cancer's metastasis, radiologists extract data for classification from a series of aligned MR images and compare the MR signature for each pixel or a group of pixels to the MR signature of known healthy and cancerous tissues. Results are presented as a color overlay to an image, or numerically for statistical validation. Images can be displayed with specific colors highlighting all the pixels or groups of pixels with similar values. By comparing the MR signature of a patient's primary tumor with suspicious lesions, cancer can be identified in other areas of the body.

Ultrasound, computed tomography, and magnetic resonance imaging each have important roles in diagnostic imaging. Many benefits are offered by more insightful, convenient, and cost-effective methods for understanding a patient's condition without further jeopardizing health with unnecessary surgery, injections, or exposure to harmful radiation. And with the data in a form that can be transmitted around the world in moments, physicians can share results and insights with ease.

IDL (Interactive Data Language) from Research Systems, Inc., is a fourth-generation programming language (4GL) used by scientists, researchers, engineers, and software developers to build data analysis and data visualization applications. IDL includes a rich suite of mathematics, statistics, graphics, image processing, mapping, and general data manipulation features in an integrated, high-performance package. Because IDL's 4GL simplifies programming and does not require the tedious edit-compile-link-debug cycle required by traditional languages, IDL lets users develop fully portable applications much faster than with C/C++ or Fortran.

IDL version 5.0 is available for the popular operating systems: Windows 3.1x, Windows 95, Windows NT, Macintosh, Power Macintosh, Unix (Sun, HP, SGI, Digital, and IBM), Linux, and Digital's OpenVMS. Windows, Macintosh, and Linux pricing starts at $1,500. Unix and OpenVMS pricing starts at $3,495. Research Systems, Inc., can be contacted by e-mail at info@rsinc.com, by phone at (303) 786-9900, or by mail at 2995 Wilderness Place, Boulder, CO, 80301.

Jon Snyder is a freelance technology writer based in Boulder, Colorado. He has published articles in Recording magazine and is a staff writer for Colorado Golf magazine. He currently works in the Marketing Department of Research Systems, Inc.

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