Question

You are viewing intravascular ultrasound images with a physician. The physician points out some very bright objects in the vessel wall with a dark region beyond it. She says, “that is a calcium deposit.” Do you think this a reasonable explanation? Why?

Answer 1

Answer:

Yes,I think this a reasonable explanation because calcium deposit is echogenic and echodense,blocks the sound waves from the ultrasound probe, reflects the sound waves back without letting them pass through and hence itself appears as bright.

The vessel wall calcium deposit also does not allow the sound waves from the probe to move beyond it to the vessel wall tissues causing acoustic shadowing(an area with no sound waves) ;that is a dark region beyond it on ultrasound.

Hence the explanation by the physician that the bright objects in the vessel wall with the dark region beyond it is a calcium deposit is a reasonable explanation.

Explanation and discussion:

Clinical scenario:Viewing of intravascular ultrasound images with a physician and the physician pointing out some very bright objects in the vessel wall with a dark region beyond it and explaining that it is a calcium deposit.

Principle of intravascular ultrasound

During the procedure of intravascular ultrasound, a very fine ultrasound probe is passed Into the vessel lumen and ultrasound images are obtained.

Intravascular ultrasound works on the principle of vessel imaging using information from the differential impedance to the sound waves transmission from the ultrasound probe by the different blood vessel wall layers and tissues and collection of these reflected waves  to form an image .The interpretation of the image is based on the understanding that tissues which reflect the sound waves most are generally echogenic (having ability to generate an echo) and appear brighter on the ultrasound image while the tissues that do not reflect the sound waves well are echolucent (do not generate echo and are permissible to the sound waves) and generally appear as a dark or black in the ultrasound image. The differential impedance of the sound waves to different tissues In the vessel wall helps in the interpretation of the vessel wall pathology and the disease process.

Normal appearance of a vessel wall:trilaminar appearance-bright-dark -bright from inside to outside.

The vessel wall has three layer from inside to outside; that is tunica intima,tunica media and the tunica adventitia.

Tunica intima is the innermost vessel wall layer,It is lined by cellular endothelial layer and some connective tissue containing elastin,and atheromatous plaque, calcium deposits with age and disease and hence is echogenic. {The plaque and calcium  are absent in very young people and hence their tunica intima cannot be detected on the Intravascular ultrasound }.This layer generally reflects the sound waves back ,so it appears brighter on intravascular ultrasound image.

The tunica media is the middle layer and is composed of smooth muscle cells which do not reflect the sound waves back and hence appears dark on intravascular ultrasound.

The tunica adventitia is the outermost layer which contains the loose connective tissue and collagen fibres. This reflects the sound waves well and hence is bright.on intravascular ultrasound image.

This explains the normal trilaminar ultrasound image of the vessel wall generally observed.

Ultrasound image and Calcium deposition in the vessel wall

Calcium deposits in the vessel wall are echodense objects ,appear echogenic and bright on the ultrasound images as they reflect back most of the sound waves emitted by the ultrasound probe.Calcium deposits do not allow the sound waves to travel beyond them.They cast a dark shadow beyond them (a region with no sound waves) in the ultrasound image which appears as the black region in the image.This is called acoustic shadowing . Keeping with these facts, it can be concluded that the explanation that the bright objects in the vessel wall with the dark region beyond it is a calcium deposit, is a reasonable explanation given by the physician.

Summary:

The explanation by the physician that the bright objects in the vessel wall with the dark region beyond it is a  calcium deposit, is a reasonable explanation based on the principle of acoustic shadowing.