News Story

Running the Numbers
MR Elastography Reveals Liver Fibrosis Prior to Cirrhosis
Product Showcase: Cone-Beam CT Scanner Minimizes Radiation Exposure
Penn Researchers to Receive 7T MRI
MRI Scan Optimization: A Discussion with Philips Medical about SmartExam

MR Elastography Reveals Liver Fibrosis Prior to Cirrhosis

A team of researchers at the Mayo Clinic (Rochester, Minn) has developed a new technique for diagnosing liver fibrosis before incurable cirrhosis sets in. MR elastography (MRE) is proving to be a worthy alternative to the old method of needle biopsy, which carries inherent risks, draws in multiple physicians, and may be inaccurate owing to sampling errors.

Conventional imaging techniques—CT, ultrasound, and traditional MRI—are not capable of detecting fibrosis. But when an MRI is combined with a device that generates vibrations inside the body, a quantitative image of tissue stiffness can be obtained.

“For centuries, physicians have used touch for diagnostic purposes,” explains Richard L. Ehman, MD, division chair of diagnostic radiology at the Mayo Clinic and a professor of radiology at the Mayo Clinic College of Medicine. “Every medical student learns that a hard mass in the breast, the prostate, or the thyroid gland is very likely to represent cancer. So, for a number of years in my research program, we’ve been working on imaging technology that would be able to do the same thing, because there are limitations to what you can evaluate by touch.”

Figure 1. Mechanical waves with very low amplitude (less than one tenth of a millimeter) are generated inside the liver and other organs by an acoustic driver, which is placed on the abdominal wall. A modified phase-contrast MRI sequence is used to image the propagating waves?in this case at 90 Hz. Here, the wave images are superimposed on an anatomic image.	Figure 2. A mathematical algorithm is used to process the wave images to calculate the stiffness of tissues. The resulting quantitative image is called an elastogram, which shows stiffness in units of kilopascals (kPa). The average stiffness of the liver in this patient with biopsy-proven hepatic fibrosis is 5.6 k, which is about twice the normal upper limit of about 2.5 kPa. The stiffness of the liver also is more inhomogeneous than normal (compare with Figure 3), and reaches more than 10 kPa in some areas.	Figure 3. This MRE of a normal volunteer shows that the average value for liver stiffness is less than 2 kPa and the stiffness is more homogeneous than in the patient with liver fibrosis shown in Figure 2.

In Ehman’s study—the findings for which were published in the August issue of Radiology¹—elastography was conducted using a device that vibrates with low-frequency sound, similar to an electric shaver; the MRI involved was a standard 1.5T system. “A few years ago, we recognized that detecting diffuse disease, like liver disease, might be a good application of this technology,” he says. “The liver responds to injury in a very stereotypical way. You get inflammation, you get fibrosis, and eventually you get scarring; if you get scarring, you end up with severe distortion of the anatomy.”

Elastography can diagnose liver disease in the fibrosis phase, when the condition is still reversible, and Ehman believes it can do so more accurately and efficiently than needle biopsy. “Think about what a biopsy involves—if it’s going to be image-guided, it’s going to involve some sort of image procedure: sterile technique, a doctor putting a long needle into the liver at least six times. Then, those biopsy specimens are going to have to be prepared, taken to a laboratory, mounted, and put on glass slides. Then another doctor, a pathologist, is going to have to look at those and render a professional interpretation. We’re talking instead about something that is a very short add-on to a conventional MR exam, requiring only a few minutes of imaging time.”

Clinical trials on the technique are ongoing. “The results that we have so far,” Ehman says, “are very impressive and very positive.”

Reference

1. Rouvi?re O, Yin M, Dresner MA, et al. MR elastography of the liver: preliminary results. Radiology. 2006;240:440?448. Available at: radiology.rsnajnls.org/cgi/content/abstract/240/2/440. Accessed October 9, 2006.

Penn Researchers to Receive 7T MRI

Researchers at the University of Pennsylvania School of Medicine Department of Radiology (Philadelphia) can look forward to the acquisition of a new “toy” in mid-2007. Thanks to a $2 million grant from the National Center for Research Resources (NCRR of Bethesda, Md), a division of the National Institutes of Health, the department will be able to order a 7T MRI system in late 2006, and hopes to have it installed and operational within 6 months. Only a handful of 7T magnets, which are approved by the FDA exclusively for research use, are in operation across the United States.

Ravinder Reddy, PhD

“Our research is pretty broad-based,” explains Ravinder Reddy, PhD, professor of radiology and science director of the Metabolic Magnetic Resonance Research and Computing Center (MMRRCC) at Penn. “It’s not going to be clinical—only research will be done on this magnet. This will vary, from developmental projects that span areas like cancer research, Alzheimer’s, and so on.” Reddy adds that researchers will be working on technical developments related to these different areas. “When the scanner comes in,” he says, “it won’t be equipped to work with a lot of coils, so we will be developing that technology and associated sequences.”

Four centers at Penn, including the MMRRCC, will be using the 7T magnet for research: the Center for Functional Neuroimaging, the Center for Molecular Imaging, and the Laboratory for Structural NMR Imaging. The project has been supported through a mixture of internal and external funding, like the NCRR grant.

A space in the lower level of the Stellar-Chance laboratories has been designated for the magnet, but a lot of preparation is still to be done before the facility is ready for it. This strength of magnet, Reddy explains, is not self-shielding like a 1.5T or 3T system, and risks are involved that aren’t a consideration with lower magnet strengths. “These are not self-shielding magnets, so they do have a big fringe field to begin with. That’s why they must have very strong, very thick metal to contain them. Nobody with a pacemaker would be allowed to walk even close to the magnet.”

Increased magnet strength doesn’t just affect researchers and patients. “The higher the field strength, the more the radiofrequency penetration will become complicated and problematic,” Reddy says. “It creates some image artifacts.”

But the advantages of the 7T system, even when it’s used exclusively for research, easily outweigh the difficulties associated with purchasing and installing it. “The major point behind going for higher field strength is that you can look at different nuclei in the body,” he says. “Traditionally, we image water in the body; water is about 70% of the body, so that’s why you get high resolution and good-quality images. But there are a lot of other nuclei in the body, like carbon, sodium, and oxygen. At lower field strengths, they have a really low signal-to-noise ratio. But as you go into higher and higher fields like 7T, you can image sodium in the body to very high resolution, and that will give significant information about disease.”

MRI Scan Optimization: A Discussion with Philips Medical about SmartExam

Arindam Mukherjee

Philips Medical Systems (Andover, Mass) calls its SmartExam technology the first MR with IQ. Intended to optimize scan quality while minimizing scan time, SmartExam is now available on the Achieva 3T, the Achieva 1.5T, and the Panorama 1T. It also can be applied to previously installed Philips Medical MR systems.

SmartExam?s features include automated planning, which detects anatomical landmarks in the survey scan and uses the information to plan the diagnostic scans around the patient?s actual position on the scanner; automated scanning, which allows the operator to define the spatial resolution that the system will then maintain without altering voxel size in a manner that might cause unwanted changes in image contrast; and automated processing, which can perform such techniques as image filtering and image subtraction automatically, as soon as the image acquisition is complete. To learn more, Medical Imaging spoke with Arindam Mukherjee, director of global sales and communication for Philips Medical?s MR business.

MI: What do you see as the key benefits of the system?
Mukherjee: The key benefit is simplicity. With one click, the complete planning, scanning, and processing are done. Why do I say that? Observe a technologist?s current workflow: The patient is put inside the magnet. Then, the tech performs a reference scan, planning the slices. The tech then takes the respective protocols?each time, clicking and scanning. Then, after finishing, the tech moves to the next protocol to click and scan. All of these steps are taken over by the SmartExam. It?s all automated.

MI: Do you have to enter any criteria for SmartExam to automatically program all of these steps?
Mukherjee: We have Exam Cards?the system basically recognizes the human anatomy of the brain and clearly depicts the complete brain structures to provide the user with the complete image. Suppose what you see, if you observe the MR, is the physician or technologist saying, ?Lay straight. The head position must be straight.? With SmartExam, that patient?s head could be tilted left or right; the system recognizes every landmark and gives a consistent image.

MI: What kind of training is required to operate it?
Mukherjee: As long as you know how to click a mouse, that?s it.

MI: Does it require a dedicated workstation, or is it a component operating on the existing MR workstation? Mukherjee: It is a feature of an MR scanner. So, if you buy a Philips MR, it will be there. On a normal procedure, the user chooses the Exam Cards, and then?depending upon what the patient is having scanned?selects the smart cards of the brain, and then clicks, drags, and drops. Then, the user clicks on the ?start scan? button, and that?s it.

MI: So, users see a lot of time efficiency.
Mukherjee: We see a 30% increase in operator efficiency. If you look at a typical hospital environment, especially in MR, the technologist is busy. He or she has to monitor the patient, see if the MR is scanning, if the patient is doing well, and if the images are coming, et cetera, et cetera. The tech must plan, and then if the slice is not done well, he or she must re-plan and redo the scan. It takes a lot of time. With SmartExam, the moment you click, you can start looking at the previous case, or something else. It gives a little more flexibility and freedom to the technologist or the operator. And if you look at it from a consistency point of view, it?s always the same result. It doesn?t change based on the individual who is using the system.

MI: How many customers currently are using SmartExam?
Mukherjee: Plenty. Some of the premier sites are the University of Michigan and the hospital in Copenhagen. In fact, I was speaking to Professor Stefan Sunaert, a radiologist at the University of Leuven in Belgium, and he said, ?I do advanced clinical research. When I used to do it before, I always had to come back to the scanner, because I had to see if the slice positioning was right and whether I?d get the right image or not. After the introduction of the SmartExam, I don?t come over at all. Now every time, I have 100%.?

MI: Are you working on the next version of SmartExam?
Mukherjee: We are always looking forward. At this time, I can make only a general statement: Philips has really focused on how to make technology simpler. But I will say that at this year?s RSNA, you can certainly look for something exciting.

For MRI products to be showcased at RSNA 2006, see this month’s cover story.