The acoustic window or field is the area defined by the pathway of the ultrasound beam between the transducer and the acoustic reflector. The sound reflection to skin boundary should be minimized with an ultrasound gel where this gel acts as an acoustic window through which the image is seen.
Acoustic window refers also to the optimal placing of the transducers so that the areas of interest are clearly imaged.

See also Transforaminal Window, Transcranial Window, Transorbital Window and Transtemporal Window.

The first step in a transcranial Doppler (TCD) examination is to localize a cranial acoustic window where the ultrasound beam can penetrate without being excessively attenuated.

There are three main transcranial acoustic windows, used for the sound beam in cerebrovascular ultrasonography to overcome the skull barrier:
A complete TCD examination incorporates these windows allowing the visualization of the complete cerebral circulation.

The transforaminal or sub-occipital acoustic window is found in the space between the atlas and the base of the skull (through the foramen magnum insonated from the top of the neck below the occiput). Practiced in the prone position (or sitting).
This acoustic window allows the insonation of the vertebral arteries, basilar artery and some of the other branches of the posterior circulation (e.g. posterior inferior cerebellar artery).

See also Transcranial Doppler.

Cerebrovascular ultrasonography is the best screening tool for the detection of carotid artery stenosis. Transcranial sonography is used in the evaluation of patients with suspected cerebrovascular disease, but a common problem is the attenuation of the ultrasound signal by the skull.
Contrast enhanced ultrasound play a particularly important role in the visualization of the intracranial vessels, and thus improves the accuracy of transcranial Doppler and increases the potential of this technique. The use of microbubbles is helpful for classification of stenosis and for plaque evaluation in patients with poor initial examination. Ultrasound contrast agents avoid misdiagnosing a subtotal stenosis, which is a very important clinical issue.

See also Adventitia, Intima, Periorbital Doppler, and Acoustic Window.

(LUS) Diagnostic laparoscopy combined with laparoscopic ultrasound is used for staging tumors and to monitor surgical interventions like for example radiofrequency ablation or cryotherapy. Laparoscopic ultrasound provides direct contact imaging of organs with high frequency ultrasound. Laparoscopic ultrasound identifies and characterizes the tumor, guides the probe, and monitors the progression of the freezing or the thermal destruction. This procedure avoid unnecessary open surgery and improves selection of patients for tumor resection e.g., in liver and pancreas.
Challenges of LUS are limitations of the intraoperative acoustic windows and the possible movement of the probe and that standard orientation techniques are difficult to apply with laparoscopic instruments, resulting in images from oblique planes. 3D ultrasound or special navigation systems may be helpful.

See also Ultrasound Therapy.