In ultrasound, which target has the best (easiest) "acoustic window"?
a. human heart
b. rabbit brain
c. dog brain
d. human thyroid

D.  Human thyroid

From the University of Arizona Health Services Center
http://www.ahsc.arizona.edu/opa/crnap/mri.htm:
"Briefly, ultrasound uses high frequency sound wherein the reflected
sound is used to create anatomic images. The technique is portable,
relatively inexpensive and sensitive to vascular flow. Ultrasound
needs an acoustic window for transmitting the sound; it cannot
effectively transmit through air (e.g. the lung) nor through bone."

The human heart, rabbit brain and dog brain are all protected by bone.
 The human thyroid gland is the neck/throat
(http://www.thyrolink.com/patients/thycare/goi/g11d.htm) and is not
protected by bone.

Thank you for your question. If you need any further clarificaiton,
please let me know.

Regards,

-THV

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