Page 88 - ITPS-7-3

INNOSC Theranostics and
Pharmacological Sciences Medical imaging technology

of the electron beam to hit a set of semicircular target spin system gradually increases from zero, and when the
rings, producing X-rays. When the X-rays pass through system reaches equilibrium, the magnetization intensity
the subject’s body, they are received by the detector group stabilizes. If the nuclear spin system is affected by external
arranged on the opposite side. Since there is no mechanical influences, such as radiofrequency excitation of the nucleus
movement, the scanning speed can be as high as 50 ms/ at a certain frequency, a resonance effect occurs. After
layer. While the temporal resolution is excellent, the spatial the radiofrequency pulse stops, the excited atomic nuclei
resolution is not as high as that of high-end third- and cannot maintain this state and return to their original
fourth-generation machines. Further, the development arrangement in the magnetic field. During this process,
of EBCT is anticipated. Some hospitals in China have they release weak energy, which becomes radio signals.
officially launched EBCT, which, due to its imaging speed When these signals are detected and spatially resolved, an
being 20–40 times faster than ordinary CT, can provide image of the distribution of atomic nuclei in motion can
exceptionally clear images of moving organs such as the be obtained. The process of returning atomic nuclei from
heart. After many generations of development, XCT has an excited state to an equilibrium arrangement is called a
been widely used in medicine. At present, it is primarily relaxation process, and the time it takes is called relaxation
used in diagnosing spinal and head injuries, intracranial time. There are two types of relaxation times: T1 and T2.
tumors, brain–blood clots, early heart disease prevention T1 is known as spin-lattice or longitudinal relaxation time,
and treatment, soft-tissue injuries, gastrointestinal and T2 is known as spin-spin or transverse relaxation time.
diseases, and malignant lesions of the waist and pelvis. Although MRI images are also displayed in different

3.2. MRI grayscales, they reflect differences in magnetic resonance
signal intensity or the length of relaxation times T1 and
Since the 1980s, nuclear magnetic resonance technology T2, unlike CT images, where grayscales reflect tissue
has been applied to clinical medicine. The strong magnetic density. MRI images can generally be divided into three
field interacts with the nuclei of the body tissue in the basic images: T1-weighted image, T2-weighted image, and
imaged part of the human body. The nuclei and their proton density image. Fat appears as a high signal in these
physiological conditions resonate under the magnetic field’s images, while muscles, liver, pancreas, and other tissues
influence and change their positions. The images generated and organs show a medium signal on T1-weighted images
by the magnetic field not only avoid the damage caused by and a low signal on T2-weighted images. Lung tissue, large
CT machines to human tissue cells but also detect small blood vessels, and calcification generally appear as low
physiological changes before pathological changes occur. signals in these images. In contrast, tissues and organs
Consequently, MRI has become a new branch of medical such as the kidneys and spleen have lower signals on
imaging diagnosis. T1-weighted images and higher signals on proton density

MRI is currently one of the most advanced imaging and T2-weighted images. The contrast of CT images
examination methods. It is an emerging imaging diagnostic depends on the X-ray attenuation properties of the tissue.
technology that non-invasively displays the internal Fat has low density, calcifications have high density, and
structure of the human body. Although this technology large blood vessels have a density similar to that of the liver
has been developed for <20 years, it has rapidly advanced, and kidneys. Tumors often have a density similar to soft
with equipment manufacturing technology and diagnostic tissue, and contrast agent injection is generally required for
theory continually improving. At present, MRI equipment better visualization and characterization.
is widely used in hospitals in large- and medium-sized The amount of information provided by MRI is not only
cities. Its high-resolution images of human tissues and greater than many other medical imaging techniques but
organs provide more intuitive image information about the also fundamentally different. Therefore, it has significant
internal structure of the human body, offering richer and advantages in the diagnosis of diseases. MRI can directly
more meaningful diagnostic and treatment information produce tomographic images of cross-sections, sagittal
for clinical use. 8 planes, coronal planes, and various oblique planes without
According to the principle of MRI, atomic nuclei are producing artifacts common in CT scans. MRI does not
positively charged, and the nuclei of many elements, such require the injection of contrast agents, exposes the patient
as hydrogen-1, fluorine-19, and phosphorus-31, undergo to no ionizing radiation, and has no adverse effects on the
spin motion. Normally, the arrangement of nuclear spin body. Compared to CT, MRI has no radiation damage
axes is irregular, but when placed in an external magnetic or bone artifacts, can perform multi-faceted and multi-
field, the spatial orientation of the nuclear spins transitions parameter imaging, offers high soft-tissue resolution, and
from disorder to order. The magnetization vector of the is suitable for diagnosing various diseases across different

Volume 7 Issue 3 (2024) 4 doi: 10.36922/itps.3360