CERN Accelerating science

Medical Imaging

Medical Imaging

A primary goal in diagnosis is to obtain the morphological and functional information about a patient through non- or minimal-invasive techniques. Medical imaging started in 1895 with the discovery of x-rays by W.C.Röntgen. Its application to radiological imaging rapidly covered during the last century all the various radiological and radioactive tracer modalities such as Digital Radiology (DR), Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Magnetic Resonance Spectroscopy (MRS), Single Photon Computed Tomography (SPECT), Positron Emission Tomography (PET), Ultrasonography (US) and many other modalities just emerging in the field, such as luminescence, photo-acoustic and Cherenkov  imaging.

Combined Modalities

The various imaging modalities are subdivided in two main categories: those that give morphological information (i.e., that provide the anatomy of the patient with a spatial resolution up to fraction of mm, such and CT and MRI) and those that give information about the functioning of an organ, of a body district or of the entire human being. Among the latter particularly relevant are SPECT, PET and functional MRI (fMRI). More and more it became evident that there is the necessity of obtain both information simultaneously and this request has driven the research to build the so-called hybrid systems, such as the CT-SPECT, CT-PET and more recently PET-MR. This new feature of multimodalities has posed more stringent requests on the detector to be used so as to have the best of the two worlds (morphology and functional behavior) in the same system.

PET-MR hybrid Imaging :( left) MR, (right) PET, (center) combined [ A.Zaidi and A.Del Guerra, Medical Physics, 38 (10), October 2011, 5667-5689.]

Translational studies in medical imaging

Most of the new techniques on the human being are first attempted on small animal imaging where a smaller instrumentation allows developing and testing of sophisticated techniques before their implementation on human scanners. In addition the study of many diseases and new drugs distribution on small animals has become a necessary prerequisite for the understanding and cure of neurological, metabolic and cancer disease, by the so-called translational study, where the finding on small animals are often the basis for the application of new type of diagnosis and therapy on human being.

CT scan of a mouse, obtained with the micro-CT XALT (CNR- Pisa, Italy)

Medical imaging in therapy

Medical Imaging has become an essential part of any treatment of any disease, not only for the diagnosis of the disease, but also for the prognosis, the therapy and follow-up. As an important example it is enough to say that not only the CT is the basis for a cancer diagnosis and personalized planning, but also an MRI and/or a PET is typically required in order to design the proper treatment in radiotherapy. Furthermore, advanced instrumentation is becoming more and more integrated in the treatment room for image guided intervention.

Cross sectional slice of a human brain obtained with a 7T MR (IMAGO7, Pisa, Italy)

What are the detector requirements?

The requirements on the detectors for medical imaging are much diversified depending upon the technique to be used. A few examples are listed below. In Digital Radiology there is the necessity of high efficiency and high spatial resolution detector for low energy 60-120 keV X-rays and even higher resolution for mammography, where a lot of research is going on for the so-called color-radiography, where the energy of each single photon is measured. In this case the detector of choice is becoming the solid state detector. In the CT application the detector must have an extremely fast response to allow for almost sub second complete CT scanner. In the nuclear medicine applications the detector should be very efficient at the higher gamma energy such as the typical 140 keV of 99m-Tc or the 511 keV annihilation gamma rays of PET. In this latter case the PET with time of flight capability is posing stringent requests of high efficient scintillators with a very fast time response. In either case digital based electronics with FPGA, ASIC etc is now a must for any imaging system. A different story is for the MR field, where the coils are the technology under continuous development. As for US imaging the miniaturization of the US probes is the main technological challenge. Finally, in the hybrid system applications the requirement of electromagnetic compatibility and non mutual interference between the two combined imaging techniques put even more stringent requests on detector development and optimization.