This is the first case report to demonstrate how MVI can be used to delineate the biliary tree and diagnose biliary reflux. As shown in this case, the use of MVI on ultrasound was a safe, quick, and accurate method to diagnose biliary reflux in a patient with Sump syndrome following previous Roux en Y Hepaticojejunostomy; a PTC, and invasive technique, had demonstrated this phenomenon.
Biliary reflux post hepaticojejunostomy (Sump syndrome) is a rare life-threatening condition that leads to recurrent episodes of cholangitis. It can occur due to the accumulation of lithogenic bile, debris, or calculi as well as refluxed duodenal contents in the distal common bile duct (CBD) . Although the mechanism is not completely understood it is thought to be due to a short Roux limb with reflux of food into the biliary tree and disturbance of intestinal motility . Early recognition of biliary reflux in patients that have had hepaticojejunostomy is crucial in the management of patients. Management may involve surgical correction and lengthening of the Roux loop. In more challenging cases, the patient is started on long term prophylactic antibiotics to reduce the recurrence of severe cholangitis episodes .
MVI technology was developed in 2014 and is based on the unique algorithm of isolating and eliminating background movement artefact known as clutter. This is different to conventional ultrasound imaging such as colour Doppler flow imaging (CDFI) and power Doppler flow imaging (PDFI), which are unable to differentiate low flow signal and clutter artefact . In the motion suppression algorithm, changes in the positions of structures are subtracted out, before a wall filter is used to suppress clutter noise and minimize flash artifact. The result is true movement – normally interpreted as flowing vessels. Compared to conventional Doppler methods such as CDFI and PDFI, MVI has the advantage of high frame rates, high sensitivity to low flow tissue signal, high spatial resolution, and low motion artefacts . When compared to CEUS, MVI has similar sensitivity to low flow signal . CEUS has improved the diagnostic accuracy of US in the detection of flow in many conditions when a crucial component for the diagnosis, for example in MVI has been applied in the assessment of focal liver lesions [8, 9], breast , thyroid , carotid plaques . and testicular pathology [14, 15]. Compared to CEUS, using MVI has advantages; being completely non-invasive, negates the administration of a contrast agent, with lower cost and can be less time consuming .
Focal liver lesions are commonly encountered and MVI has shown the ability to detect characteristic features of hepatic haemangiomas  and focal nodular hyperplasia . Intranodular vascularity in a thyroid nodule is considered an indeterminate feature and can be equivocal with Doppler imaging, studies have found that MVI has a similar accuracy to CEUS in detecting microvascular flow in thyroid nodules . Intraplaque neovascularisation and haemorrhage are predicative factors for the rupture of vulnerable plaques and therefore increased risk of strokes . Previously this could only be assessed using CEUS, however similar results can be achieved with MVI . Zhang et al noted the time necessary to observe neovascularisation was much shorter for MVI than with CEUS . Although MVI has shown excellent early results in a range of conditions, the use of MVI is still novel and therefore further multicentre studies are required to develop clinical standards for its use and correlating the findings with progress of disease and prognosis .
The resolution quality of this technique allowed an accurate diagnosis without the need for invasive investigations. Although called microvascular flow imaging, this technique can be used to look at any low flow signal, including in non-vascular structures, such as the biliary tree and the urinary system. MVI has been used to detect retrograde flow of urine from the bladder retrogradely along the ureter in vesicoureteral reflux (VUR) in children . Although CDFI has been used for this with a reported high specificity and sensitivity , it is not possible to detect low velocity and to differentiate this from clutter artefact. MVI can be used to eliminate this whilst providing high resolution and high frame rate. Kim et al  found that MVI can be used for the detection of high grade VUR and correlates with voiding cystogram, with the major advantage being a non-invasive investigation, with no catheterisation required and is less time consuming .
MVI offers a dynamic modality which is highly sensitive to movement with traditional advantages of ultrasound including spatial and temporal resolution as well as being radiation free . As a result, MVI compares favourably to more invasive and/or expensive techniques such as PTC, MRCP and small bowel studies, which are the current mainstay of diagnosis for Sump syndrome . Ultrasound has an excellent safety profile and is usually the first line imaging modality for right upper quadrant pain. The addition of MVI is quick, non-invasive, and where appropriate can help to give an accurate definitive diagnosis to guide management.