As with gynecologic ultrasound most TPUS exams are performed with the woman in either lithotomy in a standard gynecologic examination table or in a modified lithotomy position with cushion placed under buttocks and lower extremities in frog-legged position. For 3-dimensional imaging the examiner may also need to prop their arm or elbow as the imaging capture time can be as long as 15–20 s and the absolute stillness is critical for the optimal image quality. It is certainly possible to do the TPUS with a patient standing, which could be especially useful in patients who are not as successful with dynamic maneuver in supine position.

Transperineal ultrasound refers to ultrasound performed with the transducer position on the perineum. There are techniques described in literature that use translabial ultrasound, i.e., transducer is placed on the labia majora. Term introital ultrasound [10] is also used where transducer is placed at the vaginal introitus or posterior fourchette. The common denominator for all those techniques is placement of transducers externally on the patient’s vulva rather than introduction of the transducer into vagina or anal canal. For the purposes of this chapter we will focus on transperineal ultrasound and mention other types of ultrasound where appropriate for specific studies. TPUS imaging can be performed with use of either trans-abdominal curvilinear transducers or with endovaginal transducer that is typically used for endovaginal gynecologic ultrasound. Curved array transducer is typically 4–8 MHz, whereas endovaginal transducers have frequencies up to 9.0 MHz. It is important to keep in mind that higher frequency transducers provide superior resolution, but have less tissue penetration. This trade-off is important for achieving images of diagnostic quality. For the purposes of this chapter, ultrasound performed with curved array transducers will be referred to as translabial ultrasound (TLUS) as the transducer is placed over the labia majora to visualize anatomic structures. With use of endovaginal transducer the transducer is mostly placed on the perineum or at the posterior fourchette and thus we will refer to it as transperineal ultrasound (TPUS). There is no agreement in nomenclature for these techniques.

For transperineal ultrasound as with any ultrasound imaging use of coupling gel is a critical step as ultrasound waves do not pass through air. Whether trans-abdominal or endovaginal transducers are used the gel should be placed between the transducer and covering. For endovaginal transducers a disposable cover (e.g., male condom) and for curved trans-abdominal transducer glove or plastic wrap can be used. Additionally gel should be applied to the perineum to allow for better coupling. Warming the gel in a commercial warming device improves patient comfort. After each use, transducers should be cleaned and disinfected according to manufacturer recommendations.

Different techniques have been described for transperineal and translabial pelvic floor imaging. Some investigators use a curved array transducer (4–8 MHz abdominal probe) [11–13]. The transducer oriented vertically with a mark (i. e., a groove or ridge on one side of the ultrasound transducer) facing up and placed firmly against symphysis pubis. The transducer can be placed on the labia or with labia parted. With the transperineal technique an endovaginal transducer is placed on the perineum with a mark facing up. In this chapter all the TPUS images are captured with endovaginal transducer. The image optimization depends on the goal of desired visualization. With imaging of the pelvic floor muscles and levator hiatus the transducer is directed cranially (Fig. 3.16a, b) with imaging of the anorectum the transducer is usually oriented posteriorly towards the anal canal [14] (Fig. 3.17a, b). Care should be taken to avoid excessive pressure applied to the perineal structures. Most investigators advise to assure tissue contact enough to visualize anorectal structures avoiding any excessive pressure on the perineum. Compression of perineum may distort perineal anatomy and limit mobility of the pelvic floor during dynamic maneuvers.

In transperineal pelvic floor imaging the transducer is most commonly oriented with the mark facing up (12 o’clock position) with midsagittal orientation. The produced 2D image will represent anterior structures (pubic symphysis and urethra) at the left portion of the screen and the posterior structures (anorectum) at the right side of the screen (Fig. 3.17b). The 2D image produced by TPUS imaging allows for visualization of the urethrovesical junction (UVJ), anorectal angle, structures of the anal sphincter complex. This view can be used to observe pelvic floor mobility during pelvic floor maneuvers, like pelvic floor contraction (Kegel’s exercise) and during straining.

In the midsagittal view the structures seen from left to right: pubic symphysis, urethra and bladder, vagina and anorectum. On the midsagittal view the pubic symphysis cross-section is usually oblong and bony structures of the pubic rami are not visible. Next, anterior and posterior urethral walls are delineated against periurethral tissues. Usually urethral mucosa and submucosa are imaged as a universally hypoechoic structure that appears as an open lumen. Vagina is usually seen as a collapsed structure, where vaginal walls are not clearly separated by ultrasound. Anorectum is seen as outline of hypoechoic internal anal sphincter (IAS) against the midline anal mucosa, which is usually echogenic with variable echogenicity due to fold of anal mucosa. Hyperechoic external sphincter surrounds the hypoechoic internal sphincter. The anorectal angle is normally easily visualized and changes with dynamic maneuvers of the pelvic floor muscles. Cross-section of the puborectalis muscle (PRM) is seen posterior to the anorectal angle.

Three-dimensional (3D) ultrasound refers to two-dimensional static display of three-dimensional data. For acquiring and rendering 3D ultrasound dataspecial transducers and software are needed. The 3D ultrasound dataset is referred to as “volume.” To obtain 3D ultrasound the transducer is held in the stationary position at the perineum during acquisition of the volume. The scanning angle is usually set to the widest available—depending on equipment this could be between 120° and 180°. The acquisition time depends on set image quality and varies between 2 and 15 s. The patients are usually instructed to hold her breath (or use shallow breathing) through the volume acquisition phase as any motion can introduce a motion artifact. For the static 3D volume acquisition the quality of acquisition (acquisition time) should be maximized for best quality images. The faster scanning modes usually compromise quality of image but can be useful during dynamic maneuvers. When 3D volumes of dynamic maneuvers are obtained the image quality could be sacrificed for faster acquisition since the subject has to sustain the dynamic state for the length of the acquisition. The dynamic conditions most commonly used for the imaging included pelvic floor contraction and the Valsalva maneuver. When acquiring volumes during the dynamic imaging the position of the transducer at rest may need to be adjusted to allow for the capturing of the dynamic state. The best imaging is achieved by assuring that patients maintain the dynamic state without movement. Any movement from operator or the subject can introduce motion artifact.

To capture transperineal 3D US volume of the pelvic floor hiatus and the surround levator ani muscles the transducer placed on the perineum and the ultrasound beam is directed in the cranial direction (Fig. 3.17). The field of view is optimized by identifying the symphysis pubis on the left of the screen and the anal canal on the right side of the screen [15]. The operator should also maximize the midline alignment with assuring that the urethra is also visible in this view. After capturing the volume images can be stored on a compact disk or drive and assessed offline. The offline post possessing is done with equipment-specific software—this is usually proprietary software that allows rotation of the volume, thick and thin slicing of the volume, and multiple measurements. During the post-processing of volumes the 3D static images are rotated to be displayed in a symmetric orientation in the three orthogonal planes: coronal sagittal and transverse planes. A cursor dot is located in corresponding positions in all three orthogonal planes. A cursor dot allows for the exact position of an anatomical structure to be identified simultaneously in the three orthogonal planes (Fig. 3.18). One of the standardized rotation techniques described is demonstrated in the serial figures [15] (Fig. 3.19a–e).