Medical Device Daily Washington Editor

WASHINGTON — The emphasis on molecular medicine continues unabated, as a recent session at the National Institutes of Health clearly demonstrates (Medical Device Daily, June 5). And a number of the presentations at the 54th annual meeting of the Society of Nuclear Medicine (Reston, Virginia), showed that both private- and public-sector entities are pushing the boundaries of the possible, driving medical science ever close to a “Star Trek” future.

Among the presentations was the first unveiling of the first-ever images of the human brain taken with positron-emission tomography and MRI, dubbed PET/MRI.

Speaking for a team of scientist at the University of Tuebingen (Tuebingen, Germany), the Max Planck Institute (Munich, Germany), and the University of Tennessee Medical Center (Knoxville), Bernd Pichler, PhD, an associate professor who runs the preclinical imaging lab at the University of Tuebingen, described the marriage of technologies as “a tremendous leap forward in imaging capabilities.”

The machine the researchers used was developed by Siemens Medical Systems (Malvern, Pennsylvania), which provided technical assistance as well as hardware (see sidebar, this page).

The Siemens approach is to build a PET unit to fit concentrically inside the torus of an existing MRI machine, thus presenting the company with a unique marketing proposition as well as some interesting engineering dilemmas.

Speaking to a standing-room-only crowd, Pichler said that PET/MR “brings the exceptional soft tissue contrast and high specificity of MR together with PET’s excellent sensitivity in assessing physiological and metabolic states.”

Pichler said that the two-in-one machine did not exhibit a problem with degraded image quality in simultaneous scans of animal subjects, describing the resulting images as being “comparable to stand-alone systems without significant distortion” at a spatial resolution of about 3mm.

Many of Pichler’s slides showed the individual PET and MR images next to a composite image that retained the sharp detail of the MRI film and the color coding of the PET images.

The researchers had to compensate, however, for the inability of MRI to distinguish bones from air, a big problem when imaging the human thorax. The researchers made some headway on this snag by using an atlas-based approach, which relies on previous images of the patient to provide a map of the location of the ribs, and Pichler said that a technique known as support vector regression proved more useful.

Siemens isn’t the only firm chasing the PET/MR convergence.

Positron (Houston) has indicated an interest in this configuration (Medical Device Daily, March 9), and the University of Cambridge (Cambridge, UK) has also devoted some resources to this pursuit. Whether Siemens will be first out the gate with a commercially available product remains to be seen, but the firm’s collaboration with the two universities has produced all the PET/MR noise at SNM.

Should this combination make its way into routine clinical practice, scheduling for scans might become substantially easier for hospitals and radiology clinics. The concurrent use of MRI and PET detection may allow doctors to “make a more sound determination of both cognitive impairment and atrophy” in Alzheimer’s patients, Pichler said. This advantage is due to the higher degree of registration afforded by the dual-scan technology. Degree of registration is the ability of a dual-mode machine to match the two sets of images both spatially and temporally.

Another of the hopes that the researchers and Siemens have for this package is that it will help doctors determine the extent of damage from strokes and provide diagnosis of Alzheimer’s by detection of biomarkers prior to the onset of symptoms.

As one might expect, the union of two such technologies presents a number of formidable engineering challenges.

Ioannis Panagiotellis, PhD, market manager for Siemens’ high field segment, told Medical Device Daily that engineers are still working on the simultaneous scan version of this device, adding: “I do not want people to think that this is ready” for commercialization.

Panagiotellis, a published researcher, said that Siemens “used a standard 3-tesla scanner into which we have inserted the PET detector,” a procedure that may only require a 45-minute slice of a technician’s time when the device is ready for market.

Panagiotellis said that the images presented by Pichler were taken in November from one of the firm’s Trio line of 3-tesla MRI machines. He said that Siemens has sold about 400 of the Trio, giving the company a substantial starting base that will likely grow larger over the next few years.

The Trio has an opening of about 77 cm (about 30 inches) and that the PET insert will close that down by only another 5 cm, or about two inches. Siemens hopes that this space-saving feature will allow the technology to make its way into service as a full-body scanner.

“This is something new, so there are a lot of risks” in investing in this idea, Panagiotellis said, noting that Siemens anticipates that this device will not be on the market for at least another two years, maybe as many as five. On the other hand, “I’m sure we have a lot of people who will want to try it.”

“In the beginning, there will be financial challenges” to sales of the unit, he said, but declining to hazard a guess as to the initial cost of the PET insert. Given the expense, the first customers for the machine are likely to be research centers rather than clinicians.

Equipment compatibility problems cropped up a few times during development, Pangiotellis acknowledged. Most PET machines use photo-multiplier tubes to boost positron emissions for image clarity, but many conventional versions of these vacuum tubes tend to blink out in magnetic fields of less than a tenth of a tesla in intensity, according to Panagiotellis.

Siemens opted to instead use avalanche photodiode detectors (APDs), which are silicon-based detectors that can handle magnetic fields of up to eight teslas.

Owners of MRI units need not worry about their inventory of gadolinium should they opt to buy the Siemens PET add-on. Panagiotellis said PET is not affected by this contrast agent.