Nuclear magnetic resonance techniques in the clinical laboratory

A door may be opening into what could be a treasure house of diagnostic information. For many years the resonance of protons in a magnetic field has been exploited by biochemists, who have a comprehensive range of procedures to elicit all spectral responses of which spinning nuclei are capable. These responses depend on two factors; one is the immediate intramolecular environtment of the protons and the other is the main steady magnetic field enclosing the sample. The bulk responses can be observed and measured as radiofrequency emissions. For biochemical studies of small samples an extremely uniform magnetic field of considerable strength and a uniform sample are required to obtain the clearest information about the molecular environment of the nuclei giving the radiofrequency signals. The potential applications of proton magnetic resonance in clinical medicine are arising from the concept of using the other factor controlling the details of the responses — the precise strength of the main magnetic field — to elicit information about the spatial position of a small element of tissue in the human body. This is done by introducing small precisely controlled gradients into the magnetic field. With these gradients in one, two, or three dimensions, the protons emitting radiowaves at each exact frequency and phase and being detected and measured are restricted to a small spatial region. The region may be a plane, a line, or a point, depending on how the spatial information is to be used. Some of the methods of building an actual image from proton magnetic resonance information are based on those developed for X—ray computerised tomographic (CT) scanning. From a combination of skills in magnetic field control, radiofrequency analysis, and image construction a potentially powerful tool for radiologists has been created. Images of normal and pathological soft tissue can give investigative and diagnostic information related to anatomy that is without comparison from any other modality (Ref. 1 & 2). Figures 1 to 6 give examples of the kinds of image obtainable and illustrate the interest and appeal that proton NMR imaging can have to radiologists and clinicians who use and are accustomed to X—ray CT, radionuclide or ultrasound tomographic images. Figure 1 is a sagittal section of a normal head and can be compared with an illustration in an anatomy book. Figure 2 shows a metastasis in the cerebellum. Figure 3 is a transverse section of a normal head and the convolutions of the brain are clearly shown due to the strong contrast between white (white in the Fig.) and grey matter. Figure 4 shows an astrocytoma surrounded by damaged and oedematous brain. Figure 5 is a baby's head in which virtually no myelin has yet appeared and which is grossly distorted by hydrocephalus. Figure 6 shows a shrunken liver with deposits surrounded by excess fluid in the abdominal cavity. Kidney, pancreas, muscle, spinal cord, vertebral discs, the soft tissue in bone and the heart are other organs which lend themselves to NMR imaging.