Imaging Innovations




Hybrid PET-MR project marks major milestone -- and other innovations

Philips announced in November last year that the European Union-funded HYPERImage research project, of which it is the leader, has achieved a major milestone in its ambitious plan to create a new medical imaging technique called hybrid PET-MR. Middle East Health reports.

The European Union-funded HYPERImage research project aims to improve the diagnosis of several major diseases through the development of a combined PET-MR system. The hybrid PET-MR is based on the simultaneous acquisition of time-of-flight Positron Emission Tomography (PET) and Magnetic Resonance (MR) images. PET is the most sensitive molecular imaging modality, while MR now provides excellent human anatomical information, specifically soft-tissue characterisation, as well as excellent temporal resolution and a significant amount of functional information as well.

The integration of anatomical Computed Tomography (CT) and functional PET – socalled PET_CT – imaging has proven itself as a standard clinical tool. However, PET-CT has its limitations, specifically radiation dose and reduced soft tissue contrast compared to MR imaging.

The combination of a PETMR scanner can only provide accurate, reliable images when the two imaging modalities are integrated into a single scanner. It is to this end that the three-year-long HYPERImage project was established in 2008.

The project involves eight partners from six European countries and has a total budget of around EUR 7 million. The ultimate goals of the project are to advance the accuracy of whole body diagnostic imaging to significantly improve the diagnosis of several diseases, such as cardiovascular disease and cancer, and to help provide a state-ofthe- art imaging technology for future applications in therapy planning and biomedical and clinical research.

A hybrid PET/MR scanner could simultaneously deliver the anatomical and functional information achievable using state-of-the-art MR scanners (such as soft tissue contrast and physiological processes in blood vessels) and the molecular imaging information provided by PET. As a result, it would combine the best of both worlds, which could ultimately help to pinpoint and characterise disease sites within the body more accurately than is currently possible.

For a hybrid scanner that offers simultaneous PET and MR image acquisition, two fundamental problems need to be solved: the development of MR-compatible PET detectors and a method of accounting for PET attenuation (the scattering of high-energy gamma rays generated by the PET tracers by parts of the human body).

The gamma-ray detectors used in current PET scanners are based on vacuum photomultiplier tubes that do not function well in the strong electromagnetic fields found in an MR scanner. One of the focus areas of the HYPERImage project is on reducing the mutual interference between PET and MR data measurements to a level that allows undisturbed image acquisition with both modalities at the same time – and it is in this area that the project has achieved a major milestone.

Milestone

The HYPERImage team has developed a functional gamma-ray detector that meets the performance requirements of the latest time-of-flight PET scanners. The new gamma-ray detectors have been designed to be compatible with the strong static and dynamic magnetic fields that would be present in a combined PET/MR scanner. Furthermore, the team has achieved major progress with respect to MRI-based static and dynamic PET attenuation correction.

“Understanding the molecular mechanisms associated with cardiovascular disease and cancer, and the development of technologies focused on the early detection of these disease processes are the two main challenges of biomedical research,” said Professor Dr Valentin Fuster, Director of the National Center for Cardiovascular Research in Madrid (one of Europe’s leading research centres in cardiology) and the Cardiovascular Institute at the Mount Sinai Medical Center in New York. “I am convinced that the realisation of a PET/MR technology platform will significantly help to improve the precision and the moment at which disease is diagnosed, two critical parameters for the successful treatment of many diseases.”

Henk van Houten, senior vice president of Philips Research and head of Philips’ healthcare research programme explained that the “HYPERImage team’s combined expertise in semiconductor physics, signal processing and medical scanner design, together with its expert clinical knowledge, have moved the project an important step forward in the development of a new imaging tool that is intended to help clinicians diagnose and treat some of the world’s most prevalent killer diseases, such as breast cancer.

“I am proud to say that proof-of-concept of an MRcompatible PET detector took the team less than one-and-ahalf years to achieve. It clearly demonstrates that good collaborations lead to very fast progress.”

PET image blurring

The HYPERImage project will also look at reducing motion-induced PET-image blurring. The longer acquisition times for PET mean that the structures being imaged typically move during the scan – for example, as the patient breathes. This results in significant blurring of the image. Monitoring of the exact position of the relevant organs using the MR imaging could be used to significantly reduce motion-induced PET image blurring.

The HYPERImage project aims to develop acquisition and data processing techniques that will enable MR monitoring of patient motion. These will be used to correct the PET data for the effects of patient motion. The MR data may also enable the PET data to be corrected for the effects of attenuation (the scattering of high-energy gamma rays generated by the PET tracers by parts of the human body).

Such an attenuation correction is required to obtain quantitative PET images with the hybrid system. MR acquisition sequences will be developed in such a way that the PET correction data is acquired along with complementary functional MR data. These techniques will be evaluated in phantom studies and subsequently in pre-clinical studies.

“Simultaneous acquisition of complementary functional information from both PET and MR will increase the power of studies where interventions such as drug administration, sedation, experimental stimuli etc. are required,” Philips notes on the HYPERImage website. “For example, in the heart, the simultaneous highly accurate measurements of both perfusion and wall motion in response to dobutamine could have a major clinical impact.

Whole body PET/MR with dramatically improved time-offlight capability will enhance existing clinical and research applications, and will enable totally new ones. For many clinical studies (including gynaecological, prostate and brain tumours, soft tissue sarcoma, and paediatrics) MR is the preferred anatomical modality, due to the lack of radiation dose and excellent soft tissue contrast. Consequently, PET/MR is very likely to replace PET/CT in the future.

The HYPERImage consortium

The HYPERImage consortium comprises three universities (King's College London, UK; Universität Heidelberg, Germany; and Universiteit Ghent - Institute for Broadband Technology, Belgium), three research foundations (Fundación Centro Nacional de Investigaciones Cardiovasculares, Spain; Fondazione Bruno Kessler, Italy; and The Netherlands Cancer Institute, The Netherlands), a university medical centre (Uniklinikum Hamburg- Eppendorf, Germany) and the industrial partner (Philips, The Netherlands and Germany).

EU funding for the HYPERImage project, which is being provided as part of the EU’s 7th Framework Program, amounts to around EUR 5 million. The consortium partners will provide an additional EUR 2.3 million.
 

System simultaneously shows electrical activity and metabolism in the heart

A research team at Vanderbilt University in the United States has developed an innovative
optical system to simultaneously image electrical activity and metabolic properties in the same region of a heart. The system will be used to study the complex mechanisms that lead to sudden cardiac arrest. Tested in animal models, the system could dramatically advance scientists’ understanding of the relationship between metabolic disorders and heart rhythm disturbances in humans; that can lead to cardiac arrest and death, and
provide a platform for testing new treatments to prevent or stop potentially fatal arrhythmias.

The design and use of the dual camera system is described in the 1 November issue of Experimental Biology and Medicine.

“The challenge in understanding cardiac rhythm disorders is to discern the dynamic relationship between multiple cardiac variables,” said one of the co-authors of the paper and the project’s principal investigator, John P. Wikswo, PhD, Gordon A. Cain University Professor and director of VIIBRE (Vanderbilt Institute for Integrative Biosystems Research and Education). “This dual camera system opens up a new window for correlating metabolic and electrophysiological events, which are usually studied independently.”

With new funding the 13- member research team working on this 11-year-old project would have been able to purchase a pair of US$60,000 high-speed and highly sensitive digital cameras to record the changes in the metabolic and electrical activity of isolated cardiac tissue using lowintensity fluorescent dyes under conditions associated with heart failure, ischemia, fibrillation and other pathological circumstances.

Each year, 250,000 to 450,000 people die in the United States alone as a result of sudden cardiac arrest, a condition that is triggered by arrhythmia. Usually, a complex series of electrical and metabolic changes precede sudden cardiac arrest.

The Vanderbilt researchers created and tested an innovative way to visualise the electrical activity of the heart in relation to its structure and changing metabolic state under different pathological conditions. Their multimodal cardiac imaging technique uses a two-camera approach to integrate electrophysiological imaging with optical fluorescence imaging of metabolic activity associated with damaged heart tissue and tachycardia, or accelerated heart rate. The biochemical and electrochemical studies of heart tissue under controlled conditions will enhance scientists' understanding of electrometabolic cardiac disorders and their clinical treatment.

The advantages of this imaging system over others include rapid setup, twocolour image separation, high spatial resolution, and an optional software camera calibration routine that eliminates the need for precise camera alignment. The authors provide a detailed description of a camera calibration procedure along with multiple examples.

In addition, the multimodal imaging system will be a lessinvasive, instrumental tool in helping scientists discover and test safe and effective ways to prevent or treat arrhythmias. Current treatments include medications that can produce undesirable side effects and the implantable cardioverter defibrillator.  


 Date of upload: 26th Jan 2010