Centers' need for volume requires balancing speed and image quality

May 1, 2007

Striking the right balance between quality and throughput is never easy, especially when the queue of referrals seems never to end. Shorter scan times mean that another patient or two could be squeezed onto the day's work list.

Striking the right balance between quality and throughput is never easy, especially when the queue of referrals seems never to end. Shorter scan times mean that another patient or two could be squeezed onto the day's work list. Cut too many corners, though, and the extra detail 3T promises simply might not be possible. When economic factors get added to the mix, the quality/throughput tug-of-war starts all over again.

Dr. William Orrison, a radiologist at Nevada Imaging Centers, prefers to take advantage of the added value that 3T imaging can offer. His drive for excellence means that patients examined at 3T generally spend a longer time in the magnet than those who are being imaged at 1.5T. The main exceptions are specialty brain imaging sequences, such as diffusion tensor imaging and functional MRI, that gain significantly from 3T's improved signal-to-noise ratio.

"These exams are very much shorter at 3T than they would be at 1.5T. So we take advantage of the speed there. But, in general, we always try to keep the quality of our 3T work higher than the very best that you can get at 1.5T," he said.

The quality of studies generated at 3T is certainly impressing subspecialty referrers, notably neurologists, neurosurgeons, and orthopedic surgeons, Orrison said.

"This is the fastest growing segment of our referral base," he said. "Subspecialists are sending patients for a 1.5T scan and finding it doesn't show anything. They then order a 3T scan and find something. They are now ordering the 3T straight off."

Many patients scheduled for 3T MRI at Fletcher Allen Healthcare in Burlington, VT, have already undergone other scans elsewhere that failed to answer their clinical problem. Radiologists consequently ramp up the resolution as much as possible, said radiologist Dr. Steven Braff.

"For seizure protocols, for example, we might get down to just over 0.5-mm in-plane resolution," he said. "Certain applications, such as routine knees and shoulders, we are happy to scan at resolution equal to 1.5T but faster. But a lot of our brain work is done at the highest possible resolution that the patient can tolerate."

Scans acquired at 3T for the Zwanger-Pesiri Radiology Group on Long Island should achieve equivalent resolution or higher quality than those acquired at 1.5T, according to Dr. Steven Mendelsohn, the group's medical director. Exactly how far staff will push for quality depends on the day's work list.

"If our schedule is not that full and we have the time, we will increase the resolution or add extra pulse sequences. But if we have a busy schedule-a throughput of maybe three or even four patients per hour-then we go for speed," he said. "On average, I would say that by using 3T instead of 1.5T, we can fit one additional patient into a two-hour scheduling window."

At Aachen University Hospital in Germany, Thoralf Niendorf, Ph.D., prefers to use the time saved from faster imaging at 3T to improve the clinical value of MR studies. Radiologists' ultimate goal should be to streamline bread and butter imaging, then use that extra time to gain more information about the disease they are evaluating, he said.

"For example, our cardiovascular MRI workup previously consisted of simple anatomic imaging and an assessment of cardiac function. Today, we are doing perfusion-weighted imaging to detect myocardial perfusion deficits, while also pushing for noninvasive tissue characterization," he said.

The standard MR-based assessment of cardiac function is one area that could usefully be streamlined at 3T, according to Niendorf. Movies of the beating heart are typically made from a collection of 10 to 12 sequential 2D slices, with one slice acquired per breath-hold. The imaging session lasts approximately 12 minutes. Higher SNR from 3T has made it possible to move to whole-heart 3D imaging in a single breath-hold.

BALANCING THE BOOKS

Claims of streamlined workflow are exactly what hospital accountants and practice managers want to hear. This is particularly true in the U.S., where reimbursement for MR studies is completely independent of the scanner used. Public and private insurers may pay for a knee MRI, for example, but the size of the check will be the same whether the exam was performed on a 0.5T open unit, a 1.5T system, or a 3T scanner. Yet the capital outlay for each of these systems can be very different indeed. From a business perspective, 3T will be a success only if radiology departments and imaging practices can either leverage more referrals simply from having a higher field system or speed up their scans.

Three-T research at the Duke University Medical Center is focused on finding ways to reduce exam time. One approach is to tweak parameters and protocols on a trial-and-error basis. An alternative approach, and the one being pursued at Duke, is to exploit the quality of 3T in key sequences so that other sequences can be cut altogether.

"If we do one very good MR cholangiopancreatography sequence that answers all our questions, there is really no need to do the other five that we usually do as well," said Dr. Elmar Merkle, director of body MRI at Duke.

Body MRI is the first area the Duke researchers are scrutinizing for possible time savings. A detailed evaluation of all neuroradiological, musculoskeletal, and vascular applications will follow. Merkle is hopeful that all protocols performed at 3T will have been streamlined and optimized within the next 12 months.

The economic argument against 3T is stronger in U.S. outpatient centers. The 2005 Deficit Reduction Act, which went into effect on Jan. 1, limits the technical component reimbursement that stand-alone clinics can receive for carrying out imaging procedures. In real terms, this means that centers could get 25% to 30% less for each MR study they perform. Hospital-affiliated centers and radiology departments are unaffected by this legislation.

The change couldn't have come at a worse time, according to Orrison. Awareness is growing of the genuine clinical value of 3T, and referrals for centers that have invested in high-field systems are growing. Yet the flat fee reimbursement system, coupled with the DRA, provides no incentive for centers to upgrade their technology and respond to this demand.

"I'm willing to make less money," he said. "But for insurers to pay the exact same price for technologies that are so dramatically different doesn't seem to make any sense if you are trying to provide the highest quality care for patients."

A more equitable solution would be to take account of quality in reimbursement payments, Orrison said. Centers opting for 3T have five to 10 times the capital outlay of practices purchasing a 0.3T system. But the difference in clarity between studies performed at the different field strengths is dramatic as well. So why not recognize this through the reimbursement system?

Setting up such a scheme would, of course, require considerable thought. Simply weighting payments according to field strength would not be sufficient.

"It is possible to take a 1.5T system and generate images that are not much different in quality from those you would get from a 0.3T system. That's what you get if you do very short sequences to get patients through as quickly as possible. The sequences that you are doing have to be quality sequences," Orrison said.

Multiscanner outpatient centers that can offer 3T benefit from the extra dimension that high-field MRI provides, said Dr. Manuel Rose, a radiologist and founder of Rose Radiology Centers in Florida. Three-T systems generate superior quality images of the chest, abdomen, pelvis, breast, vasculature, and small body parts compared with those acquired at 1.5T, he said. Rose Radiology's own 3T scanner is being used to look at myocardial wall motion and tumors of the myocardium.

"That's something that only 3T can do," Rose said.

Debate continues over whether these imaging advantages merit the increased outlay post-DRA. Businesses thinking of shelling out need to ask some hard questions, according to Rose. Practices that are just setting up or seeking to replace a solitary magnet might be well advised to stick with 1.5T. Established clinics that want to extend their scanner portfolio should consider 3T only if they expect to see a sufficient number of patients and know they can demonstrate the value to patients and referring doctors.

"It's great to have 3T technology, but with ever-decreasing reimbursements, you must have the volume and throughput to stay in business," he said.

Ms. Gould is a contributing editor of Diagnostic Imaging