Can't see anything?
In this section we’ll cover some basic mistakes on starting to use translabial/ transperineal ultrasound. The very first step would be the selection of an adequate probe cover. Condoms are generally suitable, but the reservoir at the tip of the condom can be in the way and produce artefacts. Gloves need to be checked individually since powder and certain forms of coating can result in strong reverberation artefact (Figure 1). Sometimes coating is dissolved by the ultrasound gel, which results in slowly improving conditions over several minutes.
If the image looks very confusing, it’s worth checking whether the image orientation is correct. An easy way to check is to identify the transducer orientation by using a finger on the transducer surface. Figure 2 shows an image that is oriented the wrong way round. If the image is dark in some zones of the image and not in others, then there probably is a problem with the time gain compensation settings, which usually are controlled with a set of horizontal control levers.
Next we’ll have to make sure that the transducer is in firm contact with the perineum and the symphysis pubis. The distance between transducer surface and symphysis pubis should be at most 1 cm. Greater distances will result in a poorer image (see Figure 3). Air between probe cover and transducer surface will result in reverberation artefacts over part of the field of vision, knocking out a sector of the image (Figure 4). This requires removal of the probe cover, more diligent spreading of gel over the entire transducer surface, and re-application of the probe cover.
At times, a full rectum / stool impaction can make translabial imaging very difficult, not the least by impeding organ descent on Valsalva. In such situations it may be best to defer the examination until after a bowel motion has been achieved, if necessary after using laxatives or an enema. Video 1 shows an enterocele that only becomes evident after bladder and bowel emptying.
Translabial ultrasound is usually improved by the use of harmonics (Figure 5), speckle reduction (Figure 6) and crossbeam imaging (Figure 7). Optimal resolutions require 2 focal zones placed within the first 5 cm of depth.
After transducer placement and confirmation of good conditions as suggested above, a cough will help expel bubbles and detritus, reducing artefact, and also show how much organ descent to expect as a bare minimum on Valsalva. It is is sometimes easier to be sure of what to expect after a cough, since levator co-activation (2D Basics) is much less of a problem on coughing. Video 2 demonstrates a false- negative prolapse assessment due to levator co-activation, indicated by the fact that the distance between symphysis pubis and anorectal angle shrinks rather than increases on Valsalva. One way to avoid missing a prolapse is to ask the patient to cough repeatedly, which in this case demonstrates the prolapse. As mentioned in Chapter ‘2D US Basics’ , this may require imaging in the standing position.
Video 1: Optimised prolapse assessment after bladder and bowel emptying. There is an enterocele which only becomes visible after voiding and defecation.
Video 2: False- negative prolapse assessment due to levator coactivation. Repeated coughing demonstrates a cysto- and rectocele.
Figure 1: Suboptimal probe cover: Reverberation artefact, dark image at maximum gain (left). Much improved image after change to non-powdered glove (right).
Figure 2: Wrong image orientation: the symphy-sis is on the far right of the image.
Figure 3: Poor image due to excessive distance between transducer and symphysis pubis.
Figure 4: Large reverberation artefact caused by air between the probe cover and the transducer.
Figure 5: Improved tissue discrimination with harmonic imaging (right) versus no enhancement (left).
Figure 6: Improved tissue discrimination with Speckle reduction imaging (right) versus no enhancement (left).
Figure 7: Improved tissue discrimination with crossbeam (CRI) imaging (right) compared to SRI only (left)