Hybrid PET and MRI imaging on the horizon: Shows promise for the detection of cancerous tumors

ScienceDaily (June 6, 2011) — Preliminary research presented at SNM's 58th Annual Meeting is breaking new ground for the development of a brand new hybrid molecular imaging system. Simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) is providing important diagnostic information about soft tissues and physiological functions throughout the body. Scans focused on screening suspicious lesions for cancer are already comparable to more conventional molecular imaging methods. Further research could lead to the clinical use of PET/MRI as an additional tool for detecting cancer and other diseases.

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"Combining MRI technology with PET in a single integrated system adds the advantages of the extremely broad spectrum of diagnostic MRI procedures to the arsenal of available PET procedures," said Alexander Drzezga, MD, TU Muenchen, Munich, Germany, lead author of the study. "This could potentially result in the development of new imaging agents that bring together specific diagnostic strengths of PET and MRI. It offers exciting scientific options to image physiologic and pathophysiologic processes at the same time and to improve our understanding of both. This and further studies could potentially open a whole new hybrid imaging discipline within the field of nuclear medicine."

The most commonly used hybrid molecular imaging technology is the PET/CT system. MRI shows some advantages for combination with PET when compared to computed tomography (CT), which uses X-ray technology to capture structural information but it is not as sensitive as MRI data in terms of soft tissue contrast. CT images of certain areas of the body -- including the brain, head and neck, and pelvis -- provide restricted resolution of anatomical structures. MRI technology is excellent for imaging these complex areas of soft tissue and may provide answers to unresolved musculoskeletal questions. In combination with PET, MRI may also have value for imaging liver and breast tissues and would provide a useful tool for imaging children due to its reduced radiation dose.

Simultaneous PET and MRI imaging has been a tricky business, as the magnetic field of MRI technology has limited PET imaging in the past, specifically the photomultipliers needed for data acquisition. Previous prototypes have been simply side-by-side designs or were solely for imaging the brain. The advent of "avalanche photodiodes" and their introduction to the new, fully integrated and whole-body PET/MRI prototype used in the current study is a leap forward for this technology. A number of these integrated scanners are available for research purposes worldwide. It is speculated that these systems will grow rapidly in number if clear clinical benefit continues to be demonstrated.

For this study, eleven patients with cancer diagnoses underwent dual-imaging single-injection PET/CT imaging followed by PET/MRI imaging. Simultaneous PET/MRI acquisition was feasible and offered good-quality PET and MRI diagnostic data. Tracer-uptake was similar in relation to lung, liver, spleen and bone scanning, all acquired within a short examination timeframe. Results already indicate that combined PET/MRI shows comparable performance in the detection, diagnosis and allocation of suspected tumors in patients with oncological diagnoses as compared to conventional PET/CT.

The next step for PET/MRI is studying the added benefit of introducing sophisticated MRI sequences to the diagnostic imaging protocol. This and other related studies may lead to the establishment of hybrid PET/MRI imaging as a new diagnostic imaging system similar to PET/CT for its effectiveness and ability to provide a wealth of both functional and anatomical information about the body.

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New molecular imaging agent targets cornerstone of cancerous tumors

ScienceDaily (June 13, 2011) — A study introduced at SNM's 58th Annual Meeting may lead to the next wave of cancer imaging by helping to develop a molecular imaging agent that detects many malignant cancers' incessant development of blood vessels -- a process called angiogenesis. A protein biomarker known as CD105 has been shown to indicate tumor angiogenesis in cancer patients.

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"Non-invasive molecular imaging is a critical component of 21st century personalized medicine, and one of the hallmarks of cancer is angiogenesis," says Weibo Cai, PhD, assistant professor of radiology, medical physics and biomedical engineering at the University of Wisconsin-Madison's School of Medicine and Public Health. "CD105 is considered by many to be the best biomarker for evaluating tumor angiogenesis. Non-invasive imaging of this protein's expression could potentially play a variety of roles in the future of cancer patient management. CD105-targeted imaging agents also represent a new paradigm for the assessment of cancer therapies that target tumor angiogenesis. Applications for this agent could reach far beyond cancer and open many new avenues for future research."

Malignant cancers are defined by their ability to grow like weeds, forming fast and strong networks of blood vessels that carry oxygen and nutrients to the cancer's insatiable cellular structure. Endoglin, or CD105, is a naturally occurring protein that resides on the cell's surface. Above-normal expression of this protein is associated with poor cancer prognosis in more than 10 solid tumor types. The clinical standard for evaluating tumor angiogenesis is microvessel density (MVD) analysis, which is conducted by staining CD105 in tumor tissues that have been obtained by either surgical removal or biopsy. This study represents the first of its kind to report preliminary data on the non-invasive imaging of CD105 expression with positron emission tomography (PET), which provides a reliable measure of angiogenesis in the tumor.

Researchers used the medical isotope Copper-64 (64Cu) to label an antibody called TRC105, which binds to CD105. The full name of the agent is (64)Cu-DOTA-TRC105. The TRC105 antibody is currently being studied in a U.S. multicenter phase 1 human trial and multiple phase 2 therapy trials are planned or already underway for a range of cancer types. The current study specifically marks the effectiveness of using 64Cu-DOTA-TRC105 to gauge tumor angiogenesis. Results of the study showed this PET imaging agent to be highly effective, with rapid and persistent CD105-targeted uptake by tumors in mice.

Not only could this potentially be a turning point for cancer imaging and therapy, but some other major causes of death like heart attack, stroke and atherosclerosis also actively demonstrate the over-expression of CD105. Molecular imaging of this protein could one day lead to expanded tools for the detection and treatment of any number of diseases characterized by enhanced angiogenesis.

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