Question

USES OF DIAGNOSIS
*uses
*problems
*glomerular
*boumans capsule
*uses of variation

Answer 1

Proper interpretation of ultrasonography images depends on a basic understanding of how ultrasonography images are generated. For diagnostic ultrasonography, high-frequency sound waves are generated and received by the ultrasonography transducer, which is placed on the skin. Returning sound waves (echoes) are processed by a computer and displayed on a computer screen. A gray-scale image is produced when the ultrasonography machine operates in B-mode, or brightness mode, in which returning echoes are represented as bright dots; the brightness of the dots represents the strength of the reflected echoes. Echogenicity, therefore, refers to how bright or dark something appears in the gray-scale image; the brighter something appears, the more echogenic it is. With regard to the kidney, echogenicity generally refers to how bright or dark the kidney parenchyma appears in comparison to the liver.

Normally, something that reflects most of the sound waves back will appear the brightest (i.e., white); for example, fat and fibrous tissue are very echogenic and are therefore some of the brightest-appearing structures on ultrasonography images. The renal capsule consists of thin fibrous tissue, which is next to fat, and thus the kidney often appears to be surrounded by a very bright rim on ultrasonography when there is a difference of acoustic impedance relative to the adjacent tissues. Solid organs, such as the liver and spleen, have intermediate echogenicity, and the kidney parenchyma, consisting of the cortex and medulla, is normally isoechoic (equal in brightness) or hypoechoic (darker) compared with the normal liver (2–4) or normal spleen. Thus, liver and spleen echogenicity must be normal for comparison to be valid; in particular, fatty infiltration of the liver can increase its echogenicity, making evaluation of the echogenicity of the right kidney more difficult. The cortex and medulla of the kidney generally have the same echogenicity, although the medulla may be slightly darker (5,6); both kidneys should have similar echogenicity to each other. The renal sinus in the center of the kidney contains fibro-fatty tissue and thus appears very bright relative to the kidney parenchyma. Bland fluid (e.g., simple cysts), urine, and blood are anechoic (black); therefore, the medullary pyramids, which contain urine in parallel tubules, appear as dark pools between the cortex and renal sinus. (See Figure 1 for the normal echogenic appearance of the capsule, parenchyma, medullary pyramids, and central renal sinus.) Blood clots in the urinary space will appear echogenic compared with the surrounding fluid; relative to the renal parenchyma, an acute clot is hypoechoic, while subacute and chronic clots are echogenic (brighter than renal parenchyma).