Radiodensity of Common Tissues Copy

. . As a measure of the radiodensity of a particular tissue, we will introduce a commonly used measurement of density called the Hounsfield Unit. This represent a quantitave method to evaluate a given lesion on the CT so that you can categorize it as “consistent with”……… fresh blood, old blood, muscle, calcification, fat, CSF, air, normal brain tissue, etc. The Hounsfield Unit of a particular area of the CT scan can be computer generated and retrieved by the X-Ray technician with the click of a mouse. For a summary of visual shades as well as the Hounsfield Unit as it relates to the CT images, please see Illustration 132. You will notice that many of the unit ranges are overlapping and therefore by no means is the Hounsfield Unit valid for diagnostic purposes…………… …….however it is extremely valuable to aid you as you attempt to narrow down the differential diagnosis.

. . Tissue………………………………Hounsfield Unit………………..Color Shade on CT

Bone……………………………….+1000 to + 3000……………………white

Liver…………………………………40 to 60

Brain Tissue……………………….20 to 45

Fresh blood…………………………40

Muscle………………………………..10 to 40

Kidney…………………………………30

Old blood……………………………………………………………………….gray

Infarcted (old) brain tissue

CSF……………………………………..15

Water…………………………………….0

Fat ………………………………………-50 to – 100

Lung……………………………………. -700

Air………………………………………. – 1000…………………………….black ….

Illustration 132 RADIODENSITIES OF COMMON TISSUES