New developments in cardiac SPECT improve image quality, reduce acquisition time, and increase its appeal for physicians.
For some time, the medical field has viewed SPECT as the familiar, but less exciting, approach to diagnosing heart disease. Having made only incremental improvements over the years, SPECT has paled next to flashier modalities, such as CT, MRI, and PET.
“Familiarity breeds contempt, and SPECT hasn’t changed a lot compared to the razzle-dazzle of new technology,” said Jack Edward Juni, MD, FACNP, chairman and chief technical officer of CardiArc Inc, Canton, Mich. “But we think that SPECT has a reason to move into the limelight again.”
Juni attributes this transformation to new developments in SPECT that are doubling or tripling its resolution while reducing the time needed to acquire images. In addition, SPECT avoids some of the issues that are problematic in other modalities, such as the expense of MRI or the high radiation doses associated with CT.
SPECT equipment emerged from the Mark II single-photon-emission tomographic scanner developed in the 1960s by David E. Kuhl, MD, and Roy Edwards; the work also helped give birth to PET. The device utilized a gamma camera, versions of which are still in use today. “Other than the intrinsic problems having to do with the sensitivity of the crystals and what kind of collimator is used, right now, the standard cameras are all about the same. They’ve all moved away from photo tubes toward a more digital format rather than analog,” said Mathews Fish, MD, medical director of nuclear medicine at Sacred Heart Medical Center in Eugene, Ore.
Resolution has not historically been optimal in SPECT, a situation attributed in part to the technology as well as the available radiopharmaceuticals and dosing limitations. “The ability of the detector to resolve spatial details—the sharpness of the image—is affected by the detector and collimation, which acts as the lens for the camera,” Juni said.
The traditional method of acquisition has also been problematic. Patients are required to lie still, on their backs, with their arms overhead for anywhere from 15 minutes to a half-hour. Invariably, there is some movement that can negatively impact the quality of the images. “If they move during that time, and many people do, it can blur the image and cause artifacts that look like abnormalities,” Juni said.
Cardiac imaging also can be challenged by anatomy. “There is soft tissue attenuation and overlying noncardiac activity, such as the diaphragm and the bowels, that can get in the way of the heart,” Fish said.
And, as in many other areas of medicine, obesity presents another obstacle. “As patient size becomes an issue, a larger field of view is a challenge,” said Ron Noll, nuclear medicine marketing manager for GE Healthcare, Waukesha, Wis.
Yet, newer developments in SPECT technology have overcome these challenges and resulted in advances that hold promise for both the technology and patients. “SPECT is an old familiar dog, but it has a lot of new tricks ahead of it yet,” Juni said.
Software Advances with Volumetrix
Software is one area where advances can result in significant improvements in image acquisition and quality. This summer GE Healthcare will launch Volumetrix Suite, a software solution using advanced algorithms and faster PC computing that expands the capabilities of the GE Infinia Hawkeye 4, a SPECT/CT hybrid system. Its two applications include Volumetrix 3D, which integrates 3D visualization into the nuclear medicine workflow, and Volumetrix IR, which permits registration of CT studies to SPECT images.
Using Volumetrix 3D, physicians can create interactive 3D volume-rendered images of SPECT/CT and SPECT/PET studies; include objects of interest or remove obstructions for easier visualization using automatic and segmentation tools; and export 3D visualizations in a variety of standardized formats, such as jpg, tiff, and avi.
Volumetrix IR permits physicians to use the Hawkeye 4 data to automatically register SPECT/CT exams acquired at different times for simultaneous, synchronized study comparison as well as register SPECT studies to CT DICOM volumes (or the “CT of choice,” Noll said) in the proper format. Users can apply shifts, rotations, and magnification transformations to the registrations and conduct manual correction if needed.
The 3D rendering and motion reduction and correction improve image quality while cutting acquisition time in half, according to Noll. “There are lots of tools to manipulate the data and manage the image better to see the entire patient and make an accurate diagnosis the first time,” Noll said. Technicians benefit as well as physicians as they are able to quickly assess and confirm whether an exam has been compromised and needs corrections. “At the end of the day, you have a more informative and recognizable method of recognizing SPECT/CT exams,” Noll said.
Patients benefit, too, from shorter acquisition times, and in some cases, fewer exams. “Often, prior to the SPECT/CT procedure, patients have a contrast-enhanced exam. With Volumetrix’s registration capabilities, there may be instances at facilities where they are able to bring in a study already done on the CT and utilize that,” Noll said.
Putting on his marketing hat, Noll cites three c’s of benefits: clarity, choice, and convenience. Clarity results from features such as 3D fusion rendering, segmentation, and clip-and-cut planes. Choice is enabled by the registration capabilities of Volumetrix IR. And convenience results from ease of use, from actual function to the ability to share files. The suite package runs an intuitive user interface on which users can be trained in 1 to 2 days, Noll notes.
Because the product is new to customers—it is expected to launch in June—ROI has not been quantified yet, but GE expects that savings will result from reductions in the time required for reading and interpretation. GE also expects the software suite to impact future SPECT imaging. “I would say that this package paves the way to an almost complete transition to nuclear medicine hybrid SPECT imaging and may also trigger demands for ultrafast SPECT imaging in the future,” Noll said.
CardiArc Builds New Hardware from the Ground Up
That future, however, is now. CardiArc has introduced the CardiArc scanner, which can complete SPECT scans in as few as 3 minutes. The device still employs basic SPECT imaging principles but applies them differently to create a completely new machine. “The CardiArc design came from my dissatisfaction with the ways things were—I’ve read more than 40,000 studies—and so the innovations didn’t come from engineering but were driven from the end user point of view,” Juni said.
|The CardiArc system, which features a small footprint and protective lead shielding, can complete SPECT scans in as little as 3 minutes.
That inspiration has resulted in some significant differences between the CardiArc scanner and traditional devices. Most apparent is the smaller footprint. Traditional SPECT machines require large spaces, rooms anywhere from 12 feet x 16 feet to 14 feet x 19 feet, Juni said, adding that this infrastructure is typically not available in private physicians’ offices without knocking down walls. CardiArc’s minimum room size requirement is 6 feet x 7 feet. “You can actually use it in that room,” Juni said.
The small size means that not only is the device friendlier to private practice, but it also can be used in the emergency department. “You can image a patient complaining of chest pain easily in an ER cubicle,” Juni said.
Built-in shielding protects those in the immediate area. Traditionally, nuclear radiology has had no protective regulations like those required for x-ray, CT, and MRI, such as lead shielding or separate operator rooms. Rather, the technologist monitors personal exposure with a badge system. Unfortunately, the main exposure for the technologist is the patient, who becomes a source of radiation once injected with the tracer. “The only way technologists have to lower exposure is to keep some distance between themselves and the patient, which often means being out of the room,” Juni said.
The CardiArc system incorporates lead shielding that permits the technologist to stand next to patients without risk of exposure from them or the machine. “They can see the patient, talk to them, and comfort them if needed,” Juni said.
Technologists also find their job is easier with the new system since they no longer need to position the detectors for individual patients. One of the biggest challenges, according to Juni, is positioning the detectors on a nuclear scanner close to the patient’s chest. “The closer you are with any nuclear scanner, the sharper the images. As you start to move away, they get blurry very quickly,” Juni said.
Patients are not round, however, so technologists have had to program the camera to maintain the closest orbit without actually touching the patient. “There is always the tendency to keep the detector farther away so it does not bump into the patient,” Juni said. The CardiArc system does not require this programming; the only adjustments needed are to the height of the chair. Elimination of this step not only means better images are ensured—adjustments can be particularly challenging for the inexperienced technologist—but they also save time. “Sometimes half of the time spent on a scan can be spent on positioning,” Juni said.
Improved workflow benefits both the technologist and the patient, but the biggest advances come from the imaging acquisition technology itself. “In a regular system, you have one or two detectors, each weighing about 500 to 600 pounds. These are on gantries that move around the patient, creating a complex mechanical situation with moving gears, motors, cables, etc,” Juni said. The complexity can result in frequent failures. “We wanted to make our system more reliable and less intimidating.”
CardiArc’s system uses sodium-iodide detectors (although a prototype has also been designed using CZT solid-state detectors) mounted in the scanner in a 180? arc. Between the patient and this detector arc is a thin sheet of lead with six narrow slots that rotates back and forth. The slots collimate the photons with each slice, and the movement obtains views from every angle. Between the lead and the detectors are horizontal lead vanes, which create an ultralong bore collimator effect.
“Everything is stable except for one part of the collimator [the lead arc], which weighs about 30 pounds,” Juni said. The result is increased reliability and better images. “The images are intrinsically sharper than other systems—three times sharper. So we can get by with fewer counts, which means you can do the scan faster or use less tracer and radiation, or do a little of both,” Juni said. Scans can be completed in 3 minutes using half the typical dose or in 6 minutes, halving the dose again.
Shorter scan times also mean less chance for motion artifact. “About one-third of patients have significant motion problems that have the potential to change the interpretation of the final scan on traditional systems,” Juni said. CardiArc patients are less likely to move because of not only shorter scan times but also the new design.
The device requires patients to sit upright with their arms resting out from the body rather than to lie supine with their arms overhead. “Patients compare the experience to the position taken sitting in a hot tub,” said Terry Garner, CardiArc’s vice president of sales and marketing.
The experience is also less intimidating. Traditional systems can provoke anxiety, requiring patients to lie down with machinery moving over and around them. “People tend to get claustrophobic. With CardiArc’s system, one side is always open, and they can get up and walk away if they feel the need to. Just knowing that reduces the need,” Juni said.
The system has already received 510(k) approval from the FDA for use in diagnosing coronary artery disease as well as determining prognoses and risk stratification. Experienced technologists can learn to use the system for these indications in about 3 to 4 hours, Garner estimates.
The cost is different, too: CardiArc is priced lower than most systems on the market, an achievement Juni attributes to the technological advances. At today’s reimbursement rates, Juni calculates a return is possible in 1 year scanning 1.3 patients per day. More patients will naturally lead to a faster return.
Juni expects the machine to help physicians to treat more patients in a day. The faster scan times and smaller footprint create little burden on the office, and the quick result alleviates patient anxiety.
“By designing from the ground up, we’ve kept the machine affordable at a much higher performance,” Juni said. He recalls that in the early stages of development, many physicists told him his goals could not be achieved. “But it is not just a theoretical or academic exercise. It’s real,” Juni said. The old modality has new life yet.
SPECT Software: Improving Quantitation
In a paper published early this year in the Journal of Nuclear Cardiology, Mathews Fish, MD, medical director of nuclear medicine at Sacred Heart Medical Center, Eugene, Ore, and colleagues concluded that “there are differences in myocardial-perfusion quantification, diagnostic performance, and degree of automation of software packages.”1 This means that if a physician were to interpret an image using different SPECT software programs, the normal/abnormal call would likely be similar, but any quantitation may be different.
“Quantitation at this time is helpful in two ways. It acts as a check to point out minor changes that may have been overlooked during the visual inspection, and when there is an abnormality, the quantitation is much more accurate versus someone’s eyeball estimate,” Fish said.
The differences in the programs’ quantitation methods lie in the algorithms used to generate polar plots. Other disparities are found in the method of myocardial sampling, the patient populations used to derive normals, the generation of the automatic segmental score from polar map data, and the approaches to find the left ventricular valve plane and the valve’s end.
Fish is working with Piotr J. Slomka, PhD, an associate professor of medicine at the University of California, Los Angeles, David Geffen School of Medicine, and a research scientist with the Artificial Intelligence in Medicine research program of the Department of Medicine at Cedars-Sinai Medical Center, Los Angeles, to develop more robust automatic quantitation that also features some level of quality assurance.
An example of this work was revealed in a study published in 2005 in the Journal of Nuclear Medicine in which researchers led by Slomka concluded that “automated quantification of the defect extent on myocardial perfusion SPECT images can reliably detect infarcts and measure infarct sizes.”2 In another study, Slomka’s team found that “simplified quantification achieves performance better than or equivalent to visual scoring or quantification based on per-segment visual optimization of abnormality thresholds.”3
“It’s a whole redo. These programs have been tweaked and modified, but nothing really new has come out until this work,” Fish said.
Renee Diiulio is a contributing writer for Medical Imaging. For more information, contact .
- Wolak A, Slomka PJ, Fish, MB, et al. Quantitative myocardial-perfusion SPECT: comparison of three state-of-the-art software packages. J Nucl Cardiol. 2008;15(1):27-34.
- Slomka PJ, Fieno D, Thomson L, et al. Automatic detection and size quantification of infarcts by myocardial perfusion SPECT: clinical validation by delayed-enhancement MRI. J Nucl Cardiol. 2005;46:728-735.
- Slomka PJ, Nishina H, Berman DS, et al. Automated quantification of myocardial perfusion SPECT using simplified normal limits. J Nucl Cardiol. 2005;12(1):3-4.