Introduction
Computer tomography (CT) angiography is widely accepted
as the gold standard for the examination of patients with
suspected pulmonary embolism (PE) [1]. The advantages of
CT are obvious: it is widely available, the method is fast, and it
is highly sensitive for the diagnosis of PE. In fact, in clinical
studies, the sensitivity of CT angiography is reported to range
between 53 % and 100 %, while its specificity ranges between
83 % and 100 % for diagnosing PE [2, 3]. Indeed, high
contrast within the pulmonary artery is essential to diagnose
the presence of PE with CT angiography. Moreover, insufficient
contrast enhancement in the pulmonary artery maymimic a false-positive embolus [4]. Pulmonary circulatory status
is highly dependable on cardiac output and intrathoracic pressure
conditions, which are variable during different breathing
manoeuvers. Discussion of different factors influencing the quality
of pulmonary CT angiography is a subject of ongoing debate,
and there are partially contradictory research results [5–7]. From
the physiological point of view, the prerequisites for optimal
contrast within the pulmonary artery are quite clear. While administering
the contrast medium via venous access over the
upper extremity (most popular venous access is the back of the
hand or antecubital vein), the maximum amount of contrastenhanced
blood should flow through the superior vena cava
(SVC) into the right atrium, and a minimum volume of noncontrasted
blood should reach the heart from the inferior vena
cava (IVC). Evidently, the proportion of non-contrasted blood of
the IVC in relation to the SVC influences the dilution of contrast
medium in the right atrium, the ventricle, and finally in
the pulmonary artery (PA), also called the “transient
interruption of contrast bolus” [7].
Summarising numerous publications, expiration followed
by the apnoea phase seems to be superior to other respiratory
manoeuvers. Various pulmonary CT studies have been conducted
confirming that contrast in PA after expiration with
apnoea is improved compared to inspiration with apnoea
[5–7]. However, the discussion is controversial and has not
yet been conclusively resolved [8–10].
In order to evaluate the influence of standardised breathing
manoeuvers, including the newly introduced suction against
resistance scheme here, we planned to quantify the blood flow
rates in the SVC and IVC. For this purpose, we used an MR
quantification method without radiation to further investigate
the physiological background.
Finally the goal of the study was to determine the optimal
breathing manoeuver yielding the lowest IVC/SVC blood
flow ratio, thus, potentially allowing improvement of
contrast-enhanced exams in the future.