There’s a revolution in medical imaging. The technology is moving into areas that were unheard of not long ago, driven by rapid advances in DSPs, FPGAs, analog front ends (AFEs), and a host of other analog and mixed-signal semiconductor ICs. Also assisting are developments in image processing software and algorithms that are enabling complex 3D and 4D imaging formats.
Scanning techniques such as ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), X-rays, positron-emission tomography (PET), and radiology are changing the way medicine is being practiced. In a recent survey conducted by Dartmouth University and Stanford University, leading general medical internists ranked MRI and CT scanning technologies as the most valuable recent medical innovations.
Imaging systems, which can cost a million dollars or more and take up a lot of space, are evolving into less expensive products that can fit onto a cart that can be used in a doctor’s office, at a patient’s bedside, or in a local clinic. Portable handheld and laptop-computer-based imaging systems also are beginning to appear on the market. They can be tailored to fit a patient’s size, weight, age, and other unique characteristics as well.
For example, a reclining-chair MRI is now possible for arms and legs thanks to a development out of the University of California at Davis (Fig. 1). This setup takes the anxiety out of most patients who are apprehensive about entering the classic “tunnel” MRI scan, which can cause claustrophobia. Moreover, the system is designed to provide maximum imaging quality and power while the patient is relaxed. The scanner is manufactured by CNI Medical Systems which has been purchased by GE Healthcare.
A booming worldwide aging population and the need for cost-effective gear are pushing the development of smaller, more accurate, and faster-acting imaging diagnostic equipment (see “Imaging From The Medical Community’s Perspective”). Semiconductor IC technology, with its relentless drive to be smaller, faster, and cheaper, is answering the call.
It’s All In The Silicon
According to Veronica Marques, communications manager for the Texas Instruments (TI) Medical Business Unit, semiconductor IC technology has been at the forefront of improving the performance of medical imaging systems. She cites three distinct trends: the need for higher-resolution imagery for better diagnostics, faster data throughputs for quicker diagnostics and minimal patient discomfort, and the use of innovative techniques to produce smaller scanners that dissipate less power for more cost-effective solutions.
Scanner performance improvements combined with system innovations have made scanning procedures not only quicker to perform, but also a lot safer for the patient. CTs and MRIs have reduced radiation dosage levels by as much as 75%.
Tremendous progress has been achieved in integrating multi-channel low-noise amplifiers, voltage-to-current amplifiers, and multi-channel analog-to-digital converters (ADCs) into single AFE ICs. TI’s AFE58xx AFEs for ultrasound scanners are 40% smaller and dissipate 50% less power than earlier-generation parts, yet they also provide twice the performance (Fig. 2).
The Analog Devices AD9279 also reduces system complexity, power consumption, and footprint for high-end, mid-range, and portable ultrasound systems. The fourth-generation, low-power, eight-channel receiver integrates data-conversion circuitry with low-noise, time-gain, control-mode performance while providing high-dynamic-range I/Q demodulators that reduce the power and area for implementing continuous-wave (CW) Doppler processing.
“This fourth-generation part introduced in 2007 addresses the need for ultrasound scanners for a given small package size,” says Scott Pavlik, strategic marketing manager for Analog Devices’ Health Segment. “It provides the highest available output-referred large-signal signal-to-noise ratio (SNR) of up to 67 dB, enabling improved sensitivity in diagnostic scanning while reducing printed-circuit board (PCB) space by up to 40%.”
Some companies like Microsemi, which recently acquired Actel, employ FPGAs for multi-channel ultrasound imaging. The SmartFusion family of flash-memory-based FPGAs use proprietary algorithms as the basis for 4D ultrasound imaging. Furthermore, the company says flash-based memory is not as susceptible to errors caused by radiation as SRAM-based memory FPGAs.
More recently, Samplify Systems made available the SAM2032, a 32-channel beam-forming receiver ASIC for ultrasound imaging (Fig. 3). The company says the SAM2032 is the first such device on the market. It consumes 50 mW/channel, which represents half the power dissipated by competing devices. A single SAM2032 can sample data at rates up to 50 MHz and can be daisy-chained for more channels. As of this writing, Samplify Systems’ ultrasound business has been purchased by a management team within the company and has formed a new company called Cephasonics Inc. The new company has acquired all Samplify Systems’ ultrasound-related technology and intellectual property (IP); IC, module and system products; and customers, distribution and partnership relationships.
Software Providing A Helping Hand
Even software algorithms are getting into the act via the use of image-processing algorithms. Samplify Systems offers the Prism CT compression algorithm implemented in its aforementioned SAM 2032 32-channel beam-forming ASIC. It provides better lossless and lossy compression of medical sensor signals than existing solutions, depending on how much cost savings are desired in the bill of materials (BOM).
According to Al Wegener, founder and chief technology officer of Samplify Systems and Electronic Design Contributing Editor, BOM cost savings for a CT, MRI, and digital X-Ray scanner employing the Prism algorithm in a lossy mode can be significant while generating clinically acceptable images (see “Next-Generation Ultrasound Will Rely On Real-Time Compression” at electronicdesign.com).
Lower but still significant BOM savings are also possible using lossless compression that provides even higher-quality images (see the table). Wegener points out that “lossless compression of medical sensor data becomes attractive when sensor signal compression can halve the sensor data rate.”
Developments out of the Mayo Clinic have led to an advanced image-processing algorithm that can give radiologists all of the information they need when performing perfusion CT scans, yet it results in 20 times less radiation dosage. A typical CT perfusion procedure lasts about half a minute and scans the same body tissue many times, with each scan at a low dosage level. Perfusion scanning involves the passage of fluids like iodine that act as contrast agents through the blood. The fluid concentration is used to calculate blood volume and flow to detect injuries to blood vessels or tumor responses to treatments.
Algorithm development for medical imaging is also being pursued in the lab. The Research Laboratory of Electronics for the Massachusetts Institute of Technology (MIT) has developed an algorithm that cuts MRI scanning time from 45 to 15 minutes. The algorithm uses images from the first scan to produce a subsequent image. The algorithm’s software looks for features that are common to all different scans, such as the basic anatomical structure of the bodily part being scanned, so it doesn’t repeat a previous but identical scan, saving time.
In a different venue, software may yet lend a bigger helping hand in medical imaging. Microsoft has assigned a project team to explore touchless technology to help surgeons in the application of medical imaging. The aim of the project is to explore the use of touchless interaction with surgical settings, allowing images to be viewed, controlled, and manipulated without contact, through the use of camera-based gesture recognition.
The technology would alleviate if not eliminate the need for surgeons to sterilize their environment when they normally come in contact with devices like keyboards, mice, and touch-screen surfaces, requiring them to “re-scrub” themselves. At the same time, surgeons wouldn’t have to depend on others for image manipulation.
More Slices For Clearer Images
Compared to about a decade ago, CT and MRI scanners have increased their “slice count” dramatically, leading to faster and clearer images. “Four slices then was a big deal. But now we have 320-slice machines that are boosting image quality, and the count keeps rising,” says Analog Devices’ Scott Pavlik.
Products like Analog Devices’ ADAS1128 current-to-digital converter address the low-power and low-cost needs of CT scanners with high slice counts and clearer images (Fig. 4). This is invaluable for doctors who can quickly and accurately diagnose cancers, cardiovascular diseases, and musculoskeletal disorders.
“This 24-bit data-acquisition chip provides an unparalleled increase in speed from 6 ksamples/s to 20 ksamples/s and supports more channels than other products, resulting in a 50% reduction in the cost of a CT scanner’s electronics compared to older designs,” explains Alain Guery, director of Analog Devices’ Health Segment.
With MRI imaging, non-magnetic devices must be used to obtain high-resolution images in the presence of a strong magnetic field produced by an MRI scanner. Texas Instruments had this in mind last year with its ADAS6253 high-resolution ADC when it made available a non-magnetic package option (Fig. 5).
The quad-channel 16-bit device, designed specifically for high-end medical imaging applications, samples at 100 Msamples/s and has an SNR of 84.6 dB full scale at 10 MHz. Available in 9- by 9-mm quad flat no-lead (QFN) package, it dissipates just 380 mW/channel suiting it for compact imaging systems. The ADC can be switched between 14-bit and 16-bit resolution modes.
Portability In Vogue
In general, medical imaging systems are trying to bring scanning technology closer to the patient, so the patient doesn’t have to go as far to get to the technology. This is a natural and logical trend given the shrinking size of semiconductor ICs that offer more powerful and less expensive electronic functions.
Sonosite Inc. has taken the portability approach to medical scanning a step forward with its 10-lb EDGE ultrasound system for physician’s offices and bedside procedures. Its 12-in. high-resolution LED display, 14 transducers, and proprietary algorithms support a wide range of examinations and procedures, including include thoracic and assessment for pathology, vascular access, needle aspiration and injections, and abdominal cardiac, nerve, OB/gyn, musculoskeletal, and vascular scanning.
InfraScan’s Infrascanner 1000 portable scanner can rapidly screen patients with traumatic hematoma brain injuries (Fig. 6). Approved for use by the U.S. Food and Drug Administration (FDA) last December, the battery-operated handheld and non-invasive unit allows quick patient screening and acts as an adjunct to a CT scan. It “up-triages” patients suspected of brain hematomas for further CT scans and monitors patients who need emergency neurosurgical intervention.
The Infrascanner detects hematomas by using near-infrared (IR) technology based on the differential absorption of the left and right parts of the brain. Normally, the brain’s light absorption is symmetrical. Where additional extravascular blood is present, which can occur with brain injuries, there is a greater local concentration of hemoglobin and the reflection is commensurately smaller. This differential is detected via sources and detectors placed on symmetrical lobes of the skull.
In the future, terahertz rays (T-Rays) may find greater use in medical imaging. These systems emit terahertz radiation and are the technology behind present-day full-body security scanners. They’re generally expensive. Also, they release low power, require cooler operating temperatures, and are energy hogs.
A joint development out of two research facilities promises to change these requirements. Scientists at the Institute of Materials Research and Engineering (IMRE), a research institute of the Agency for Science, Technology and Research (A*STAR) in Singapore, and the Imperial College of London have developed a new way to create terahertz waves that can operate at room temperatures and are stronger and more efficient.
Such progress points to the use of T-Rays to scan and sense molecules like those present in cancerous tumors and living DNA. That’s because every molecule exhibits a unique signature in the terahertz range. Moreover, terahertz imaging is safer than CTs and MRI scans and conventional X-rays.
Imaging From The Medical Community’s Perspective
The World Health Organization (WHO) reports that the number of people age 60 and over is set to balloon to from 650 million in 2006 to 1.2 billion in 2025. Many of these people are expected to need medical healthcare in a doctor’s office, their homes, or a local clinic to avoid escalating hospital medical healthcare costs. Teleradiology and telemedicine are poised to fulfill this growing demand for better access to healthcare services.
The confluence of improved molecular imaging and the increasing popularity of teleradiological and telemedical services have pointed to the need for better access to medical records, particularly images. Although the 2009 American Recovery and Reinvestment Act has catalyzed the process of digitizing medical records including images with $19 billion in financing, fewer than 10% of U.S. hospitals have adopted this method of record keeping, even in its most basic form.
Many U.S. physicians, particularly emergency room doctors who are on the frontline of emergency medical care, use off-hour teleradiological services. The scanned images of their patients are transmitted off-hours to sub-specialty radiologists residing in other countries, worldwide. The results are faxed back to the senders, providing quick and very accurate diagnoses.
Computer-aided diagnosis, which is now in the research stage, promises to make the interpretation of medical images even more efficient. It uses different learning software that compares new medical images to older ones that have already been identified by radiologists with abnormal symptoms or lesions. It has proven very useful in detecting different types of cancers like those of the breast, lungs, and melanoma, as well as vertical fractures and intracranial aneurysms.
Though the demand in the medical community for teleradiological services in the U.S. is growing, the supply is lacking. That’s because few U.S. hospitals have adopted this technology. Telemedicine is another related field poised to expand and reduce increasing healthcare costs. It involves the interaction of doctors and their patients through video conferencing, as well as sometimes the use of medical imaging devices.
Dr. Yadin David, IEEE Senior member and founder of the Center for Telehealth and e-health Law in Washington, D.C., urges healthcare providers and technologies to agree on standards for minimum system performance of telemedicine networks and platforms, along with the development of a common vocabulary to describe these technologies.
“Healthcare providers can look at the technical description of a heart pump or X-ray machine and understand whether or not it will meet their requirements in delivering quality care to a patient,” he explains.
“But how easily can radiologists, for example, understand whether or not the pixel resolution or compression rate of their video equipment will enable them to see the fine detail on images for more accurate diagnosis?” he asks. “We need to translate technical criteria into the clinical domain to make it easier for healthcare providers to relate to it.”