Magnetic resonance imaging (MRI) of the kidneys

The most common indication for MRI of the kidneys is the diagnosis and staging of neoplasms. However, CT is prescribed for the same purpose much more often. Multiple comparative studies have proven that CT and MRI are equally accurate in detecting neoplasms, but the latter provides additional information regarding the stage of the process. Usually, MRI is recommended as an additional diagnostic method if CT does not provide all the necessary information. MRI should replace it in cases where it is impossible or dangerous to use radiocontrast agents due to allergies or renal failure, as well as when radiation exposure is impossible (pregnancy). High intertissue differentiation in MRI allows for a more accurate assessment of tumor invasion into adjacent organs. Many studies confirm that MR cavagraphy without contrast has 100% sensitivity in detecting tumor thrombosis of the inferior vena cava. Unlike other intrascopic methods, MRI allows visualization of the pseudocapsule of the kidney tumor, which can be very valuable when planning organ-preserving surgeries. Today, MRI is the most informative method for diagnosing bone metastases, which should be used in observations when other diagnostic methods do not provide the necessary information or their data are questionable. MR characteristics of bone metastasis of kidney tumor correspond to those of the main tumor focus, which can be used to search for the primary tumor in observations with multiple neoplasms, when the origin of the bone metastasis is unclear.

MRI (magnetic resonance imaging) is a highly effective method for detecting and studying the morphology of any cystic formations. This is due to the ability of the method to determine the presence of fluid based on differences in the MR signal associated with long T1 and T2 values of water. If the cyst contents contain protein or blood, then the corresponding changes in the characteristics of the MR signal from the cyst contents are noted. MRI is the best method for diagnosing cysts with hemorrhagic contents, since it is characterized by a shorter T1 time, which causes a higher MR signal intensity than that of a simple cyst. In addition, it is possible to trace the dynamics of hemorrhage. Blood is an excellent natural contrast agent, which is due to the iron content in hemoglobin. The processes of transformation of the latter during hemorrhage at various stages are characterized by typical MR pictures. The signal intensity from hemorrhagic cysts on T1-weighted images is higher than from simple cysts, i.e. they are lighter. Moreover, on T2-weighted images they are either hyperintense, like simple cysts, or hypointense.

In the 1980s, a new method of visualizing the urinary tract was developed - magnetic resonance urography. This is the first technique in the history of urology that allows visualizing the UUT without any invasive intervention, contrast, or radiation exposure. Magnetic resonance urography is based on the fact that when performing MRI in the hydrography mode, a high-intensity MP signal is recorded from a stationary or low-mobility fluid located in natural and (or) pathological structures in the study area, and the signal from the tissues and organs surrounding them is significantly less intense. This produces clear images of the urinary tract (especially when they are dilated), cysts of various localizations, and the spinal canal. Magnetic resonance urography is indicated in cases where excretory urography is not informative enough or cannot be performed (for example, with retention changes in the UUT of various origins). The introduction of MSCT into practice, which also allows for fairly clear visualization of the cerebral bladder even without contrast, narrows the range of indications for magnetic resonance urography.

MRI of the bladder has the greatest practical value in detecting and determining the stage of the tumor. Bladder cancer is classified as a hypervascular tumor, due to which the accumulation of contrast agent in it occurs faster and more intensively than in the unchanged wall of the bladder. As a result of better intertissue differentiation, diagnostics of bladder tumors using MRI is more accurate than with CT.

MRI of the prostate best (among all intrascopic methods) demonstrates the anatomy and structure of the organ, which is especially valuable for diagnosing and specifying the stage of cancer of the gland. Detection of foci suspicious for cancer allows performing targeted biopsy even in cases where ultrasound does not identify suspicious areas. In this case, maximum information is obtained only when using paramagnetic contrast agents.

In addition, MRI can provide accurate information about the growth patterns of adenoma and helps diagnose cystic and inflammatory diseases of the prostate and seminal vesicles.

High-quality imaging of the structure of the external genitalia using MRI can be successfully used to diagnose their congenital anomalies, injuries, staging Peyronie's disease, testicular tumors, and inflammatory changes.

Modern MR tomographs allow dynamic MRI of various organs, in which, after the introduction of a contrast agent, multiple repeated arias of sections of the area under study are performed. Then, graphs and maps of the rate of change in signal intensity in the areas of interest are plotted on the device's workstation. The resulting color maps of the rate of accumulation of the contrast agent can be combined with the original MR tomograms.

It is possible to study the dynamics of contrast agent accumulation in several zones at the same time. The use of dynamic MRI increases the information content of differential diagnostics of oncological diseases and diseases of non-tumor etiology.

Over the past 15 years, non-invasive research methods have been developed that allow obtaining information about biochemical processes in various organs and tissues of the body, i.e., conducting diagnostics at the molecular level. Its essence is to determine the key molecules of pathological processes. These methods include MR spectroscopy. This is a non-invasive diagnostic method that allows determining the qualitative and quantitative chemical composition of organs and tissues using nuclear magnetic resonance and chemical shift. The latter consists in the fact that the nuclei of the same chemical element, depending on the molecule they are part of and the position they occupy in it, detect the absorption of electromagnetic energy in different parts of the MR spectrum. Chemical shift research involves obtaining a spectrum graph that reflects the relationship between the chemical shift (abscissa axis) and the intensity of the signals (ordinate axis) emitted by excited nuclei. The latter depends on the number of nuclei emitting these signals. Thus, spectrum analysis can provide information on the substances present in the object under study (qualitative chemical analysis) and their quantity (quantitative chemical analysis). MR spectroscopy of the prostate has become widespread in urological practice. Proton and phosphorus spectroscopy are usually used to examine the organ. 11P MR spectroscopy of the prostate reveals peaks of citrate, creatine, phosphocreatine, choline, phosphocholine, lactate, inositol, alanine, glutamate, spermine and taurine. The main disadvantage of proton spectroscopy is that living objects contain a lot of water and fats, which “pollute” the spectrum of the metabolites of interest (the number of hydrogen atoms contained in water and fat is approximately 7 thousand times greater than their content in other substances). In this regard, special methods have been developed to suppress signals emitted by protons of water and fats. Other types of spectroscopy (e.g. phosphorus) also help to avoid the formation of "contaminating" signals. When using 11P MR spectroscopy, peaks of phosphomonoesters, diphosphodiesters, inorganic phosphate, phosphocreatine and adenosine triphosphate are studied. There are reports on the use of 11C and 23Na spectroscopy. However, spectroscopy of deep organs (e.g. kidneys) still presents serious difficulties.

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