Laminar flow is non turbulent flow in arteries with blood traveling in layers or laminae. In a straight vessel, the layer in the center flows at a greater speed with subsequent layers toward the vessel wall flowing at slower speeds.

See also Boundary Layer, and Half-Value Layer.

(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.

Lateral describes a position away from the midline of the body.

Lateral resolution is the minimum separation of two interfaces aligned along a direction perpendicular (objects that are side by side) to the ultrasound beam. The lateral or angular resolution directly relates with the collimation of the beam emitted by the crystal. Lateral resolution is proportionally affected by the frequency, the higher the frequency the greater the lateral resolution.
Higher frequency transducers are used in fetal and pediatric echocardiography because the lateral resolution displays the smaller structures better. Lower frequencies are used for adults where structures are larger and the need for greater depth penetration is important.

(LVO) Ultrasound contrast agents improve the echocardiography assessment of left ventricular function and the low sensitivity of changes in left ventricular ejection fraction (LVEF). In addition, harmonic imaging techniques and automated border detection (ABD) together with contrast enhanced left ventricular opacification increase endocardial border delineation (EBD) and the results compared to native echocardiography.