Insurance companies may grouse at paying for X-ray and MRI bills, but a recent study links medical imaging to shorter hospital stays. The study, done at Massachusetts General in Boston, reports that hospital costs climbed 55% from 1996 to 2002. In that same period, imaging costs rose slightly less, 51%, despite a doubling in the number of CT and MRI scans performed annually. In fact, the study concluded that every $385 of imaging costs over a set value equated to a one-day shorter stay.

Some of those shorter hospital stays stem from procedures made possible by better imaging. Take coronary angioplasty, for instance. It's minimally invasive surgery that opens clogged arteries. The study says this image-guided therapy costs thousands less than one alternative, open heart bypass surgery. And because angioplasty is less invasive, it shortens recoveries, so more patients want it, especially those unwilling to undergo the risk and pain of bypass surgery. So interest is high in medical imaging and the study hints why: clearer pictures lead to more accurate diagnoses, and more effective treatments. Here are a few developments pushing the trends.

Ultrasound in arteries

Relatively low-resolution MRIs can locate an artery but can't reveal its interior detail — usually an area of medical interest. And traditional gray-scale intravascular ultrasound is not widely used, “Because grayscale images are difficult to interpret,” says Volcano Corporation scientist Dr. Anuja Nair at the Cleveland Clinic Foundation. “We developed algorithms that produce color-coded images from ultrasound data that provide information on tissue conditions,” she says. “For instance, when plaque is present, the system identifies what it's made of, its thickness, and location of necrosis, calcium, and lipid.”

Volcano Corp.'s engineering team developed the catheter-based system that positions an ultrasound transducer in the artery. It transmits sound at wavelengths of 40 to 75 micron or 20 to 45 MHz. An automatic pull-back machine extracts the sensor through the artery at about 0.5 mm/sec while collecting data. This allows later flythrough examinations of the entire artery.

The color-coded description of arteries developed by Nair and Dr. Geoff Vince at the Cleveland Clinic Foundation consists of four types of tissues observed in diseased conditions. For example, fibrous and fibro-fatty tissues are both stable materials. Cardiologists want to know where they are present and in what quantity. “A third condition, a necrotic core, is mainly cholesterol, micro-calcification, and dead cells — a sort of goo. Its presence is an indicator of unstable plaques,” says Nair. “And lastly, arteries may contain dense calcium. It is important to know what's in the artery because a cardiologist would not want to place a balloon or stent where it might cause a disruption to calcified plaque. Accurate information on plaque composition would help select appropriate therapies for patients. Hence the need for accurate images that can aid in diagnosis,” she says.

Cardiologists use the intravascular ultrasound for stent deployment and angioplasty. “It is the only way to see inside an artery. Previously, anything to do with artery composition was an educated guess. But our accuracies hit 90% and above for all four plaque tissue types,” says Nair.

3D images from 504 sensors

Transesophageal echocardiography (TEE) is a relatively common form of ultrasound cardiac imaging. The technique entails inserting a probe down a patient's throat and behind the heart to capture ultrasound heart images. These can reveal the condition of the heart chambers, valves, major blood vessels, and heart tissue. Although safe and fast, TEE systems only generate 2D images. This makes it impractical for guiding treatment devices. Clinicians rely on fluoroscopy (X-ray movies) to frequently and carefully reposition the TEE probe during treatments. But X-ray imaging exposes patients to radiation and requires that doctors and nurses wear bulky lead-shielding garments for up to seven hours at a time.

Biomedical engineers at Duke University's Pratt School of Engineering have created another type of ultrasound for cardiac surgeons — a 3D imaging probe. Inserted into the esophagus to get close to the heart, the probe creates 3D images of the entire heart in the time it takes current ultrasound technology to display a single heart cross-section, say researchers. The probe reportedly has potential to evaluate heart conditions and guide therapeutic treatment devices. The Duke probe can also be used to image the esophagus, rectum, colon, and prostate.

Biomedical-engineering professor and ultrasound specialist Stephen Smith said a move to 3D imaging is the next logical step. “ The real-time 3D transesophageal probe has all the benefits of 2D TEE probe without the drawbacks,” says Smith. “It generates sharp, high-contrast images of the whole heart, and helps position heart catheters and other devices at the same time.”

Biomedical engineering graduate student Chris Pua developed the probe. His team used the outer casing of a commercially available 2D probe to house their 3D model, so the casing was previously tested and approved for use. The 3D probe is tipped with a dime-sized array of 504 ultrasound sensors. Each is as wide as a few human hairs.

“Three-D imaging requires more sensors than 2D imaging but maintaining the size of TEE probes was critical so each sensor is only as wide as a few human hairs,” says Pua. The probe generates ultrasound at 5 MHz. With 504 sensors, it has greater sensitivity and a sharper image, says Smith. And because the image is large enough to encompass the entire heart, fewer “pictures” are needed. This may shorten patient time in clinics, he adds.

Spotting plaque with lasers

A laser-based fiber-optics system differentiates between dangerous and less harmful forms of atherosclerotic plaque in test patients. In addition, the minimally invasive technique distinguished brain tumors from normal tissue. The system, developed by engineers and surgeons at Cedars-Sinai Medical Center in Los Angeles and the University of Southern California, uses a technique called time-resolved laser-induced fluorescence spectroscopy. It lets surgeons use a fiber-optic probe connected to a laser to access the required locations in the body. When the probe shines its laser on tissue, researchers can record the spectrum of light the tissue radiates or “fluoresces” in response.

The emission from the tissue provides information on its chemical composition. “This information, for example, tells whether plaque is dangerously inflamed, consisting of foam cells rich in lipids, or if it's less dangerous due to a collagen-rich composition,” says researcher Laura Marcu. “For brain surgery, it lets surgeons determine the boundaries of aggressive brain tumors in real-time during surgery,” she says. This sensitive optical system eliminates the need for many biopsies and makes it easier to distinguish between similar types of tissue.

Digital slides in high rez and fast

Digital microscopy is changing medical analysis and diagnosis. For example, rather than having physicians peer into microscopes to examine specimens, a computer guides the vision system as it collects images and puts them on-screen. Digital images can also be put online for colleagues across town or across the country. Aperio Technologies Inc., San Diego, (aperio.com) is one firm developing scanners and software for microscope slide imaging. Their ScanScope, for example, uses a line-scanning method that creates digital images of entire microscope slides at giga-pixel resolutions in minutes, as little as 5% of the time of other methods, but with superior image quality and half the cost, according to the company.

Line scanning captures adjacent image stripes in a constant-velocity scan to ensure that image stripes align without introducing image artifacts. In addition, rapid and ultra-precise focusing reveals the topology of tissue samples while they are moving.

The primary obstacle to streamlining the inspection and management of pathology slides has been the lack of a practical solution for digitizing entire glass microscope slides at diagnostic resolution. Digitizing an entire microscope slide at high resolution is a formidable technical challenge partly because the resolution of a digital slide must be comparable to that available through an optical microscope. Scanning at 50,000 ppi (0.5 µm per pixel) generates a 2.7-Gbyte file for a typical 15 × 15-mm area (30,000 × 30,000 pixels). Software compresses this image into a more manageable 100-Mbyte file. The method eliminates the frequent optical aberrations along the scanning axis.

An auto-focus function requires rapid move-and-settle, along with built in holding and braking, a feature in ceramic servo motors. The slide scanner commands the ceramic servo motors on the z-axis to make many small, high speed moves to precisely follow the contour of a tissue.

Traditional image tiling scanners cannot follow the contour of the tissue as accurately as a line-scanning system because focusing is limited to one focal position per image tile.

Additionally, the a servo motor provides smooth constant velocity at slow speed. The 3-axis motion platform consists of an X-Y stage for step and scan, using precision crossed-roller bearings, linear encoder position feedback and direct-drive ceramic servo motors from Nanomotion Inc., Ronkonkoma, NY, (nanomotion.com).