Ultrasound tissue characterization (UTC) is driven by knowledge of the physics of ultrasound and its interactions with biological tissue, and has traditionally used signal modelling and analysis to characterize and differentiate between healthy and diseased tissue.

It is a relatively new technique intended to alleviate some of the problems encountered with conventional ultrasound by improving objective tendon characterization.

It does this by standardizing instrumental settings, by providing a 3D reconstruction of the tendon, and by classifying and then quantifying tendon tissue into one of four color-coded echo types based on the integrity of the tendon structure.

Ultrasound tissue characterization algorithms quantify the continuity of echo patterns over contiguous images by analyzing the intensity and distribution of relative grey levels of corresponding pixels.

•Green (Type I echoes) are normal, well aligned, and organized tendon fascicles and at least 85-90% of this echo type should be found in a healthy tendon (SDFT).

•Blue (Type II echoes) are areas of wavy or swollen tendon fascicles. They can represent remodeling and adapting tendon or inferior repair.

•Red (Type III echoes) represents fibrillar tissue (the smaller basic unit or building block of tendon). This echo type can represent partial rupture of tendon where they reflect breakdown of normal structure, or they can represent initial healing as the tendon begins to rebuild.

•Black (Type IV echoes) are areas of cells or fluid and represent core lesions where no normal tendon tissue exists.

Type I and II echoes are generated by structural reflections from larger structures (such as intact fibers), while Type III and IV are ‘interfering echoes’ from smaller entities below the limits of spatial resolution

•The aim of ultrasound tissue characterization is not to replace conventional ultrasound but, on the contrary, it is recommended to perform an evaluation with both conventional B mode ultrasound and ultrasound tissue characterization to achieve a complete picture of tendon health.

•Currently, it is used successfully in elite human athletes, such as NBA and soccer players, to monitor the health of their tendons (Achilles tendon and patellar tendons) and to guide exercise regimens post injury. In the equine field, it is used predominantly in elite sport horses in Europe, as a part of routine maintenance evaluations to direct exercise, to monitor tendon health, and guide rehabilitation following an injury.

•UTC consists of a standard linear array ultrasound probe mounted onto a motorized tracking device with a built-in stand-off pad. Due to the sensitivity of the equipment, meticulous skin prep is required, and limbs typically need to be clipped to obtain good quality images.

•The probe moves non-invasively and automatically down the tendon from proximal to distal over a 12 cm scanning distance, which takes approximately 45 seconds. As it does so, transverse images are captured at regular distances and stored in real time in a high capacity laptop for processing. Images are automatically recorded every 0.2 mm to generate a 3D tendon volume made up of 600 images.

•The tendon volume can subsequently be used for visualization of the tendon in 3D, for tissue characterization (to determine the structural composition of the tendon), and for quantification of tendon matrix integrity. The color-coded echo types provide semi-objective information regarding the integrity of the tendon matrix and reflect the underlying tendon health. Ultrasound tissue characterization can discriminate between healthy normal tendon, adaptive/remodeling tendon, and injured/healing tendon, often in cases where conventional ultrasound appears unremarkable.

•The key to this technology is to perform successive evaluations. This allows comparison of differences in tendon structure between scans.

•3D ultrasonography or volume sonography is the imaging technology which involves acquiring a large number of data sets of 2D images from patient.  After acquisition, this volumetric data can be qualitatively and quantitatively assessed with the use of many analysis tools such as surface and volume rendering, multiplanar imaging and volume calculation techniques, etc

•3D ultrasound is a medical ultrasound technique, often used in fetal, cardiac, trans- rectal and intra-vascular applications. 3D ultrasound refers specifically to the volume rendering of ultrasound data and is also referred to as 4D (3-spatial dimensions plus 1-time dimension) when it involves a series of 3D volumes collected over time.

4D fetal ultrasounds are similar to 3D scans, with the difference associated with time: 4D allows a 3- dimensional picture in real time, rather than delayed.

•During a 3D ultrasound, the patient is asked to lie down on an exam table. The obstetrician or ultrasound technician will then apply a gel-like substance to the patient’s belly. A transducer probe or wand is then placed against the belly and moved around to get the best images possible.

• The procedure can be performed in 10-15 minutes, depending on the position of the fetus. It is entirely painless and the pregnant mother is generally comfortable all throughout.

• It is perceived that the potential of 3D and 4D ultrasound has not been fully utilized till now. It is still being used as problem solving tool although it can be incorporated in routine day to day practice.

There are numerous areas in which the use of 3D and 4D can be very useful. Few of these are as follows:

Gynecology:

• For assessment of congenital anomalies of uterus.
• For evaluation of endometrial and uterine cavity (can also be done with saline infusion sono hysterography).
• For pre procedure localization of fibroids for planning myomectomy.
• For evaluation of possible cornual ectopic pregnancies.

Obstetrics

• For evaluation of facial anomalies like cleft palate and cleft lip
• Evaluation of nasal bone, ears and cranial suture.
• Detection of central nervous system anomalies.
• With the use of 4D ultrasound many facial expressions such as yawning, tongue protrusion, mouth opening, eye opening and blinking, etc. can also be studied in greater details.
• 4D ultrasound has also been used in the evaluation of fetal heart.

•As 3D ultrasound information is dependent on reformation of acquired 2D ultrasound data, it is expected that the problems which affect the 2D ultrasound like motion, unfavorable body  habitus,  shadowing  artifacts  and  suboptimal  scanning techniques also result in poor quality 3D images.

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