Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Группа авторов

the DH View

The DH View has many, if not all, the described ultrasound artifacts, including mirror image, acoustic enhancement, edge shadowing, side‐lobe and slice‐thickness (see Chapters 3 and 5). It is very important to be familiar with these common artifacts at the DH view (Figure 6.13). These same artifacts are possible at the CC view (see Figure 6.26), another AFAST view with a fluid‐filled structure (DH view – gallbladder, CC view – urinary bladder).

      Pearl: A good learning exercise is to focus on a specific artifact and then look through several DH view video clips from different patients looking for that specific artifact.

      Artifacts

       Mirror Image Artifact

      The DH view is the classic example for mirror image artifact, which requires a strong air–soft tissue interface such as between the lung diaphragm and liver (see Figure 6.13). As a result, the ultrasound machine's software displays the liver and its structures as mirrored into the thoracic cavity (see Chapters 3 and 5).

      Common DH view mirror image artifact misinterpretations include the following.

       The liver and gallbladder mirrored into the thorax and mistaken for a diaphragmatic hernia.

       The gallbladder mirrored into the thorax and mistaken for pleural and pericardial effusion, noting that a “partial” mirroring of the gallbladder can occur.

       Ascites mirrored into the thorax can be mistaken for pleural and pericardial effusion, and liver appearing as lung, noting that a “partial” mirroring of ascites can occur.

       Acoustic Enhancement Artifact

The gallbladder will make the soft tissues distal to its fluid‐filled luminal contents appear much brighter (more echogenic or hyperechoic) than adjacent soft tissues, similar to what occurs with the fluid‐filled urinary bladder (see Figure 6.26). Typically, the acoustic enhancement includes a brighter liver and sometimes B‐lines through the far‐field to the fluid‐filled gallbladder (Figure 6.14) (see Chapters 3 and 5); however, when lung is truly dry, no B‐lines should be seen through the acoustic enhancement, unless the lung is truly “becoming” wet (see Chapters 22 and 23).

Figure 6.12. Variety of typical CVC images with other relevant structures. (A) Unlabeled DH view with the CVC followed by (B) labeled view of the same image. In (C) the CVC is obvious with its near and far wall and its maximum diameter, which may be eyeballed for its approximate measurement from the centimeter scale to the right of the screen. In (D) structures are labeled and similarly positioned as in (C). In (E) the CVC is distended and conspicuous due to right‐sided heart failure. In (F) the DH view is fanned slightly from where in (E) the hepatic venous distension, referred to as the “tree trunk sign” (Lisciandro 2014a, 2016a), is apparent (see also Figure 36.8). Note how consistent the diaphragm is within the images as a landmark for proper DH view image acquisition. CVC, caudal vena cava; GB, gallbladder; HVD, hepatic venous distension.

      Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.

Figure 6.13. Mirror image artifact at the DH view. Mirror image artifact occurs wherever there is a strong soft tissue–air interface and should always be considered at the DH view. In (A) is the same image as in (D) unlabeled and labeled, respectively. The asterisks (*) show the mirroring of the liver on the other side of the diaphragm, falsely making it appear that liver is in the pleural cavity. The gallbladder is not present. In (B) is the same image as in (E) unlabeled and labeled, respectively. The asterisks (*) show the mirroring of the liver and gallbladder on the other side of the diaphragm, falsely making them appear in the pleural cavity. The mirrored gallbladder being fluid filled may be mistaken for pleural and pericardial effusion. The hepatic venous system also may be mirrored into the pleural cavity. In (C) and (F) are the last comparative images showing how the gallbladder may be partially mirrored into the pleural cavity. The question must always be asked – could I be mistaking artifact for pathology? To increase probability for a correct diagnosis, adhere to the described tenets for an accurate diagnosis of pleural and pericardial effusion (see Chapters 7, 18 and 21). Note how consistent the diaphragm is within the images as a landmark for proper DH View image acquisition. DIA, diaphragm; FF, free fluid; GB, gallbladder; LIV, liver; ST, stomach.

      Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.

Figure 6.14. Showing B‐lines along the pulmonary‐diaphragmatic interface. Acoustic enhancement requires a fluid‐filled structure, in this case at the DH view the gallbladder. In (A) multiple B‐lines are obvious along the pulmonary‐diaphragmatic interface. In (B) an even greater number almost coalesce along the pulmonary‐diaphragmatic interface. However, and interestingly, they are in the path of the beam (its echoes) and indicated by the overlain black faint arrows on the image made more evident by acoustic enhancement artifact. Note that they are not evident to the left of the image where there is sediment and soft tissue of the liver (versus a fluid‐filled gallbladder). Numbers of B‐lines indicate degrees of alveolar‐interstitial edema and need to be placed in clinical context with a complete Vet BLUE examination (see Chapters 22 and 23).

      Source: Reproduced with permission of Dr Gregory Lisciandro, Hill Country Veterinary Specialists and FASTVet.com, Spicewood, TX.

      Pearl: B‐lines that are evident within the path of acoustic enhancement in the far‐field past the gallbladder should be considered abnormal until proven otherwise and placed into clinical context unless 1–2 are seen in a giant breed. Dry lung should remain dry despite acoustic enhancement (see Figure 6.14).

       Edge Shadowing, Side‐lobe, and Slice‐thickness Artifact

      These