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**Preliminary Report for the Development of a Multiparameter**  
**Protocol for the Identification of Sinusoidal Obstruction**  
**Syndrome including Abdominal Ultrasound before and after**  
**Allogeneic Stem Cell Transplantation**  
**[PERSON] 1,2,1\({}^{\dagger}\), [PERSON] 1,1\({}^{\dagger}\), [PERSON] 1, [PERSON] 1,**  
**[PERSON] 1,1 and [PERSON] 1,  
However, survival of patients undergoing alloHST is strongly affected by their comorbidities and organ function [3; 4; 5]. Besides relapse-related mortality, transplant-related mortality (TRM) is a major concern [6]. TRM may be caused by allo-reactive T cells leading to massive tissue damage (Graft-versus-Host disease) [7], infections [8; 9] or organ failure. Veno-occlusive disease (VOD) or sinusoidal-obstructive-syndrome (SOS) is a rare but potentially life-threatening complication [10; 11; 12; 13] with mortality rates above 65% in severe cases [14]. In SOS, occlusion of hepatic vessels is caused by the destruction of local endothelial cells following the conditioning regimen's toxicity [15]. Factors contributing to an increased risk of SOS have been reviewed recently [16], but diagnosis remains challenging. Among various diagnostic criteria proposed, the most commonly used parameters have been known as the Seattle and Baltimore criteria [17; 18], whereas newer studies define modified diagnostic criteria [19]. Nonetheless, research groups like [PERSON] et al. questioned the reliability of these scores in the past as they seem to offer high specificity but low sensitivity [20]. In response, revised diagnostic criteria have been described by the European Society for Blood and Marrow Transplantation (EBMT) [21]. All these consider hepatomegaly, weight gain and increase of serum bilirubin within the first 3 weeks after transplant as diagnostic criteria. Other clinical criteria potentially present in SOS are: Elevation of serum alanine aminotransferase (ALT), thrombocytopenia and consumption of transfused platelets, esophageal varices or signs of multi organ failure [22]. That background in mind, more accurate tools for diagnosis in clinical practice are required. Measurement of the hepatic venous gradient pressure has been acknowledged for its high diagnostic precision [23] but remains an invasive method. In contrast, ultrasound imaging as a non-invasive, reliable and easily accessible method, is recommended to exclude suspected SOS [24]. Pathological findings in abdominal ultrasound described to be associated with the diagnosis of SOS include: gallbladder wall thickening, reversal of portal vein blood flow, ascites, hepatomegaly as well as splenomegaly (as reviewed by [PERSON] et al. [24]). One study investigating the value of gray scale and Doppler ultrasound in the diagnosis of SOS attributed a high positive predictive value solely to a limited selection of parameters (positive predictive value \(>\)80% only for identifiable ascites, visualization or flow record of the paraumbilical vein, and main portal vein flow reversal) [25]. Among these, only the flow recorded in the paraumbilical vein significantly correlated with the severity grade of SOS [26]. More recent reports have extended the data about sonographic changes in SOS patients by using more specific examinations like shear wave elastography, which has been described to be increased in SOS patients [27]. As this technique is not easily and broadly available, its use in clinical routine may be limited. In line with that, contrast-enhanced ultrasound (CEUS) was assessed in the context of SOS and pathologic examinations were associated with diagnostic criteria for SOS patients [28]. Recently revised criteria for grayscale ultrasound examination have been published, including sonographic measurements of the diameter of the following structures: the hepatic left lobe, hepatic right lobe, the gallbladder wall, the portal vein and the paraumbilical vein.