RSNA: PET/MR + 7T MR represents next great leap for radiology

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PET/MR Whole Body Scan - 15.14 Kb
Whole-body PET/MR scan Source: Siemens Healthcare

CHICAGO – Mechanistic imaging, which leverages imaging to understand the pathophysiology of disease, will project the specialty of radiology another leap forward, said A. Gregory Sorensen, MD, co-director of Martinos Center for Biomedical Imaging at Massachusetts General Hospital in Boston and CEO of Siemens Healthcare USA, during the Pendergrass New Horizons Lecture Nov. 28 at the 97th Scientific Assembly and Annual Meeting of the Radiological Society of North America (RSNA).

Encouraging the audience to think more broadly and into the horizon, Sorensen shared advances in neuroimaging such as mathematical models that allow neuroradiologists to go beyond visual interpretation to quantitative interpretation and other kinds of analysis.

This new capability helps neuroradiologists investigate diseases such as Alzheimer’s disease with thickness maps showing regions of brain that get thinner with normal aging and those that get thinner with Alzheimer’s disease.

At the same time, said Sorensen, “Medical imaging is under increased scrutiny and tremendous pressure to actually show its value. Increasingly, we are being asked [about] the real transformative value of imaging and where we can really make advances in human health.”

Mechanistic imaging, which is not necessarily a functional, metabolic or molecular modality, may hold the key and help physicians understand disease in a patient or population and how that disease might be treated. “Context becomes more important than the imaging technique.”

The approach is particularly appropriate for the brain because of the lack of knowledge about the brain and brain-related illnesses. Currently, imaging has little to offer for many of these diseases. “We need better tools,” said Sorensen.

Mechanistic imaging in practice
Several years ago, researchers realized that antiangiogenesis treatment for cancer was not working the way it was expected to work. “It was a mystery. Antiangiogenetic therapies don’t seem to work on their own. They only seem to act with traditional agents and there is no dose-response relationship. Giving more doesn’t give a better outcome.”

Researchers needed to understand how the therapy works to design better versions with less toxicity and improve efficacy. Sorensen and other researchers believed imaging could answer these types of questions.

He collaborated with a cancer biologist who had devised the theory of vascular normalization, which suggests that the enlarged vasculature associated with malignancy become normal with treatment.

The researchers hypothesized that there would be a window of time and dose where the antiangiogenetic effect would be visible. They used anatomic and functional imaging tools to answer the question.

Sorensen and colleagues applied sophisticated MRI techniques in a clinical trial and saw the brain become more normal with successful treatment. In fact, the researchers showed the degree of vascular normalization on first day correlated with survival, said Sorensen.

“By drilling into pathophysiology, we can help images become much more relevant,” said Sorensen.

MR/PET and 7T MRI in practice
In 2011, MR/PET holds promise in a number of applications, said Sorensen, including:

  • Pediatric PET: This dose-conscious group can avoid CT dose.
  • Pelvic oncology: CT does not display pelvic anatomy such as the ovaries well.
  • Lymphoma: These patients, often in the dose-sensitive age range of the 30s and 40s, require frequent CT scanning.
  • Alzheimer’s disease: Sorensen predicted a revolution with the availability of amyloid agents. These patients need both MR and PET scans, so it may make sense to do them together.

“7T MRI has made amazing strides in last several years,” said Sorensen.  “We can see things can’t see with 3T such as lenticulostriate arteries.”

Other examples include the effects of radiation therapy in the brain and multiple sclerosis plaques. With 7T MRI, radiologists can see gray matter disease, which has completely redefined understanding of multiple sclerosis, said Sorensen. Doing so demonstrates the value of imaging and can impact patient health and medicine.