Pictures of the Future    Fall 2007

Pictures of the Future – In Brief

A prototype medical scanner from Siemens combines magnetic resonance tomography (MR) and an imaging process from nuclear medicine, providing entirely new insights into the human brain. Experts believe this unique tool will improve the diagnosis of early-stage Alzheimer’s disease and enable physicians to more quickly assess the condition of stroke patients and propose treatments. The device combines MR (top) and positron emission tomography (bottom). MR contributes by displaying images of soft tissue in high resolution and sharp contrast, while PET highlights regions that display increased metabolic activity in very fine detail. Up until now, neurologists using PET could not conclusively differentiate between low-grade cognitive disturbances and the early stages of Alzheimer’s. They have also been unable to simultaneously measure the reduction of brain volume associated with Alzheimer’s. With MR-PET (center), this examination can now be conducted in a single step. Physicians can also use the prototype scanner to better monitor and investigate the progress of other neurological disorders, including Parkinson’s disease, epilepsy, depression, and schizophrenia. For a PET examination, a patient is injected with a very small dose of a short-lived radioactive liquid, which accumulates in cells with an elevated metabolic rate and releases positron radiation. When the positrons collide with electrons, they are annihilated, thus releasing gamma ray quanta, which are registered by a detection device that uses the data to generate a tomographic 3D image. Engineers at Siemens Medical Solutions used extremely fast and sensitive avalanche photo diodes (APD) to serve as a PET detector. These diodes are not affected by the magnetic field generated by the MR system, which operates in tandem with the PET unit at a field strength of three teslas, enabling it to deliver a resolution of approximately 0.2 mm. The images created by the two systems are then superimposed on one another by a computer to produce images containing an unprecedented level of information.