In-utero fetal MR scans are becoming increasingly common, although care must be taken to protect the fetus during examinations, according to researchers in Europe and the U.S..

With the publication rate of papers on fetal MRI accelerating rapidly, more physicians are referring pregnant women for prenatal MR examinations to confirm or rule out suspected abnormalities detected on ultrasound. While the scans avoid exposing both mother and fetus to ionizing radiation, the level of risk from the high magnetic fields has yet to be established.

Dr. Elspeth Whitby, research fellow in radiology at the University of Sheffield, U.K., recognizes the value of MRI to both patients and physicians in clarifying potential problems observed on ultrasound.

“If a patient has an abnormal fetus in-utero, she wants as much information as possible,” she said. “But it is also necessary to prepare the staff who are going to deal with that baby when it is born.”

This scenario is particularly relevant in the case of spinal abnormalities, which can be picked up easily on ultrasound but are seldom clearly defined by that modality. A prenatal MRI examination can provide essential information for the pediatric surgeon prior to the baby’s delivery and may avoid further antenatal imaging before surgery.

At Sheffield, ultrafast in-utero MRI was performed on 40 women carrying a fetus with an ultrasound-detected abnormality during the second or third trimester of pregnancy. Single-shot fast spin-echo sequences using a 1.5-tesla scanner produced 20 slices in 20 seconds and effectively “froze” the fetal movement. Such movement is a common limitation in prenatal imaging.

Although rapid sequences can reduce both scan time and motion artifacts, fetal motion may still lengthen the time patients must spend inside the scanner. Despite using an ultrafast technique, researchers at Sheffield took between 20 and 40 minutes to produce three orthogonal planes of the area of interest.

“The main problem we have found is actually letting the fetus settle,” Whitby said. “We can get nice scans in the prone and sagittal planes quickly, but by the time you have decided which the axial plane is, the fetus has moved.”

She presented results of the study during a preconference seminar at

the joint annual meeting of the International Society for Magnetic Resonance in Medicine (ISMRM) and the European Society for Magnetic Resonance in Medicine and Biology (ESMRMB), held in Glasgow, Scotland, in April.

Additional information from in-utero MRI changed the diagnosis in 14 cases, including three suspected instances of agenesis of the corpus callosum that were shown to be normal. MRI and ultrasound obtained equal information in 12 cases, while in no case did ultrasound provide more details than MRI. Postdelivery surgery performed on three babies confirmed the prenatal MRI results.

Fetal MRI gives physicians greater confidence in providing parents with diagnostic information that may influence decisions about terminating pregnancy, according to U.S. researchers from the radiology department of the Indiana School of Medicine in Indianapolis. At the Glasgow meeting, Dr. Julia Lowe, an MR technologist, and her colleagues outlined studies performed at the Indianapolis campus in a poster on prenatal MRI.

Indications for fetal imaging include oligohydramnios, renal agenesis, myelomeningocele, hydrocephalus, and Dandy-Walker malformation. Some of these conditions are incompatible with life, some will have a drastic effect of the quality of life, and others will have minimal effect on the newborn, Lowe said.

All radiologists at the Indiana School of Medicine must obtain consent from the mother before performing the MRI examination, owing to ongoing uncertainty about scan safety.

“Although there are no known hazards from MRI in pregnant women, only a small number of scans have been performed,” Lowe said. “The possibility of uncommon risks to either mother or fetus still exists.”

Dr. Janet de Wilde, research associate and head of the U.K. Magnetic Resonance National Evaluation Team (MagNET) research group at Imperial College in London, outlined the inherent difficulties of accurate risk assessment for in-utero MRI at a special session on safety during the European Congress of Radiology held in Vienna in March.

Three sources of hazard can be identified in MRI: the large static magnetic field, the pulsed radio-frequency waves, and the fast-switching magnetic fields. Given the combination of factors, working out the hazard for the fetus from a particular scanner with any specific sequence is complicated, she said.

Most reported MRI-related incidents in both the U.K. and the U.S. result from RF burns. Heat stress to both the mother and fetus from the pulsed RF field is another consideration.

“In MRI, it is difficult to ascertain the degree of heating to the fetus. It’s already quite difficult to get a good mathematical model of heating to a human who is not pregnant, so to extend that model to a patient who is pregnant is quite hard,” de Wilde said.

Although fast sequences are often chosen to overcome problems of fetal movement, fast spin-echo sequences produce more RF heating. Instead, de Wilde recommends the use of echo-planar imaging sequences, which have fast gradients and lower RF values.

Exposure to switching magnetic fields also raises concern about acoustic noise levels on the developing ear. Prenatal MRI examinations begin at 12 weeks, although hearing does not develop until after 24 weeks’ gestation.

“We can provide the mother with hearing protection, but how do we know how much acoustic noise the fetus is exposed to?” de Wilde said.

If MRI is the preferred imaging option to avoid x-ray exposure, the potential for hazards must be kept in mind, she said.

Research on aortic stent grafts is beginning to yield outcomes data, but not without a few wrinkles. Tissue surrounding grafts continues to move, twist, stretch, and shrink two years or more after stent placement, prompting the development of new designs, materials, and techniques.

Among the possible answers are sutures or screws to place stent grafts more firmly, and irradiated stents or catheter-based brachytherapy to address renal arteries and other locations prone to restenosis.

Dr. Clement Grassi, an interventional and cardiovascular radiologist at Brigham and Women’s Hospital in Boston, believes many problems with aortic stent grafts can be prevented by customizing stent configuration to the patient. Research presented at the RSNA meeting last November indicated that more than half of aortic stent grafts showed at least mild geometric distortion two years after implantation, with no signs of settling. A German team found severe or extreme changes in 8% of patients and moderate changes in 39% of 22 patients with either Vanguard or Talent grafts. Severe alterations were less common in the Talent grafts. The most common movement involved changes in angle between the attached leg and body of the graft, showing movement in the iliac arteries, and changes in angle at the graft’s midportion.

“There is a little depression about the results of aortic stent grafts for abdominal aortic aneurysm,” said Prof. Dr. Ernst-Peter Strecker, professor of radiology at the University of Freiburg in Germany. “No type of design yet guarantees good results.”

With endoleaks the primary concern for aortic stent grafts, Strecker and others are sorting out new preventive measures. Anchors or stitching to attach the stent to the aortic wall might help to prevent proximal endoleaks. Strecker is working on a screw for that purpose. Given the aorta’s width, restenosis around the site would not prove a major threat, he said.

Innovations dealing with the stent’s movement are more challenging. Body movement and the shrinking aneurysm both can jar the graft, pulling legs loose or pushing the stent up too far. Ideally, a stent would be flexible enough to ride with such movements, and its length would adjust according to the size of the aneurysm. As long as researchers are shooting for the moon, why not try packing all that adaptability into something that can collapse small enough to be easily introduced through the iliac arteries?

Monitoring the stent’s status, according to Strecker, consigns additional hardships to the patient, with several CT scans per year for follow-up.

“Cynically, I would say the stent graft becomes a new disease the patient has,” he said.

Restenosis, meanwhile, remains a threat for stents in other parts of the body. While radiating stents have shown some promise, new cell growth may proliferate just beyond either end. Coated balloons may work, and localized gene therapy shows promise, Grassi said.

Strecker added that European researchers are investigating stents that can be built to release growth-inhibiting drugs over time. Clinical trials with dexamethasone and cytostatic drugs have been started in Germany with promising early results.

Stenting is also making inroads in the ostium of the renal artery, where it is showing better patency than angioplasty. Other researchers are investigating stenting in the bronchii, rectum, and large bowel. Stenting may also be an alternative to carotid endarterectomy, which remains expensive and risky because of the threat that microemboli might enter the brain. Several cerebral protection devices, including balloons and filters, have been developed to reduce the risk of stroke and other complications during the intervention.

“So far, there is no proof that the procedure is superior to surgery, or less expensive, but the hospital stay will be shorter, and many trials are under way,” Strecker said.

Interactive computer-based teaching programs can provide an effective and efficient way of training radiologists at their desks, according to experts in the field of medical informatics.

While medical education is often characterized by hours spent in busy lecture halls and costly trips to external training centers, online tutorials eliminate the need for course participants to gather in person, saving both money and time.

In late 2000, Dr. Steffen Achenbach left the department of diagnostic radiology at Philipps University in Marburg, Germany, to set up his own business in Web-based learning for professionals. He expects that the new-style teaching packages will be welcomed by the hospital-based doctors and physicians in private practice who have to pay for hotel accommodation, meals, and travel to attend traditional medical training courses.

“The major spending for participants on the former courses was not the course fee, it was the rest of the expenses,” said Achenbach, who is now a company director of Samara Academy in Hamburg.

His confidence in the power of the Internet to revolutionize education is based on his experience working in a computer company before training to become a doctor. While completing his internship and postgraduate training at Marburg, he developed a Web-based teaching database that let radiology students track the changes of disease on imaging via patients’ virtual records.

Although his new business venture will focus initially upon training for information technology professionals, Achenbach recognizes the growing need for doctors to learn how to surf the Web quickly, and for medical institutions to maintain network security. As a former ECR course tutor in Internet search strategies, he is hopeful that many of the technical products will also appeal to radiologists. His plans provoked a lively discussion at the Management in Radiology meeting in Parma in October, where he received widespread support.

“My professional colleagues told me, ‘If you have the chance, then you should do it!’“ he noted.

Small group size, on-site learning, and interactivity are key elements in effective training, according to Achenbach. The Samara Academy courses are being designed for six remote participants plus one trainer. An online training platform on the Web allows the trainees to share and discuss documents out loud, while teaching is enabled with voice-over IT.

“It’s not interactivity between a person and a computer, it’s interactivity between people, and that’s an important point,” he said. “It makes you think and learn and gives you the pressure to do something for the group.”

To run the programs, participants must have a desktop PC fitted with a Pentium III processor and a good Internet connection, preferably an ISDN line. Achenbach acknowledges that availability of high-speed Internet connections remains a stumbling block in many parts of Europe, but he is encouraged that the communications industry is promoting fast online access.

Interactivity is also central to an online tutorial developed at Humboldt University in Berlin, to help medical students, trainee radiologists, and doctors recognize the cost implications of radiology in diagnostic decision-making. As users decide which diagnostic procedures to perform in individual cases, the clinical consequences are recorded and cost calculations performed. The online tutor function provides advice throughout the program to prevent unnecessary procedures and false diagnoses.

Inclusion of cost-effectiveness in the training package was prompted by the introduction of diagnosis-related groups (DRGs) into the German healthcare system, said Dr. Ulf Teichgraber, an instructor in radiology at the university’s Charite Campus Virchow-Klinikum, who described the online tutorial at ECR 2001. Where reimbursement is based upon standard rates assigned to DRGs, reduction of unnecessary procedures becomes increasingly important.

“If you have the right diagnosis and exceed the cost, then there will be an analysis of the procedure, which will be done by the tutor,” Teichgraber said.

The program, written and designed by Dr. Maciej Pech, an IT expert at the Charite, was showcased on the ECR’s Golden Mile. Although the software is still being evaluated, the response from students and physicians at the Free University in Berlin and Humboldt University has been positive. A questionnaire returned by 26 registered online users demonstrated high acceptance of the system.

At present, the master program is available on CD-ROM, and a download version is in preparation. All extensions to the program, to update cost information or add new cases, can already be downloaded from the Web. Radiology trainees and medical students will benefit from fast access to up-dated data via the Internet, Teichgraber said.

Taking multidimensional ultrasound beyond the ubiquitous baby face, researchers have illuminated lesions and abnormalities throughout the abdomen and beyond. Romanian radiologist Dr. Dragos Camen used a 3.5-MHz, low-threshold scan of a 77-year-old man to reveal a 10-mm stone in the bladder. Similar scans have yielded detailed 3-D images of renal calculi, bladder papillomas, and a reconstructed, sliceable prostate.

© 2001 CMP Media, LLC
6/1/01, Issue # 1704, page 7.