Topics and Speakers Jacqueline A. Bello, MD
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Synopsis
Combining physics and aesthetics, neuroimaging illuminates the stark beauty of the brain's anatomy. Dr Jaqueline A. Bello provides an in-depth examination on the radiographic anatomy of the central nervous system while incorporating the biophysics of neuroimaging throughout the talk. Throughout, she illustrates the concepts discussed with real life case studies and challenges the audience to correctly interpret the scans.
Regardless of the modality-magnetic field in MR or X-rays in CT-images come from delivering an energy source to some body tissue. As the energy passes through, the body tissue alters the energy. Detectors surrounding the body collect data from the tissue about how it interacted with the energy. Whether interpreting CT and MR scans, Dr Bello emphasizes that it is imperative to know whether contrast was given.
Dr Bello begins with a discussion of computed tomography [CT]. An X-ray passes through the brain, whose tissue geography has been divided into a grid. Every time an x-ray passes through the brain, a detector on other side reports how the x-ray exited the body. By compiling data from all the detectors using a back-solving algorithm, scientists can determine what type of tissue exists in each section of the grid. They then assign one of 16 shades of gray to each pixel, in a measure of volume called a voxel. The resulting image maps out the different tissue types in the brain and illuminates whether there is a pathological formation, such as an infarct or tumor, present. Thus, CT density is dependent on tissue-specific x-ray attenuation. This helps not only to characterize, but also to date lesions.
Dr Bello describes two cutting edge types of CT. Spiral CT allows continuous information to be recorded without any skips. The patient moves through the scanner while beams wrap around the head. Multislice CT, the next development after spiral CT, offers other advantages. As indicated by its name, multislice CT takes multiple x-ray slices, up to 64, of the brain at once. This technology makes it possible to get greatly enhanced resolution using the same exact speed, same exact dose (power). It also permits the image to be displayed in various planes.
Magnetic resonance [MR] imaging works by manipulating and analyzing the protons in the human body. As Dr Bello points out, the body is 70% water. In their natural state, the protons in water are randomly oriented in many directions, resulting in no net charge. Once in the MR scanner, these protons are manipulated in two ways. In the first technique, called T1 relaxation, the scanner flips the protons 90 degrees and then analyzes how they relax back. Protons relax differently in different types of tissue. In the second technique, T2 relaxation, all the protons are organized in a uniform orientation. The detector then measures how long it takes them to return to complete randomness.
By examining T1 and T2 relaxations together, MR determines the type of tissue present. Each type of tissue has signal characteristics of proton relaxation. In addition to characterizing lesions, MR can be used to localize and date lesions.
Taken together, these two forms of neuroimaging offer powerful tools for both basic and clinical neuroscience.
