Our study evaluated the ability of two cardiac MRI techniques, TWIST, and 3D post-contrast whole heart, in the evaluation of patients with superior cavo-pulmonary anastomoses regarding patency of Glenn shunt and presence of veno–veno collaterals compared to MSCT angiography findings. We found that 3D post-contrast whole heart has a statistically significant agreement in qualitative and quantitative assessment for both Glenn shunt and veno–veno collaterals. While TWIST showed lower agreement due to the improper timing of contrast bolus tracking, either due to arrhythmia, improper movement, kyphoscoliosis, or small size of the veno–veno collaterals (< 4 mm in size).
MSCT angiography
MSCT angiography is the gold standard imaging modality in the evaluation of cavo-pulmonary anastomosis and related complications such as thrombosis, stenosis, and development of veno–veno collaterals. The main advantages of MSCT angiography are the short acquisition time, high spatial resolution, and ability to image patients with various metallic stents, pacemakers, and defibrillators [2].
It has been reported that MSCT angiography is an accurate and reliable noninvasive examination in the assessment of morphological changes in patients with Glenn shunt, regarding visualization, stenosis, and thrombosis [8, 15].
The major disadvantage to MSCT angiography is the use of ionizing radiation. Despite technological progresses that have decreased radiation exposure, for young patients that will require serial imaging, the cumulative radiation dose remains a concern. MSCT angiography always requires the use of iodinated contrast, which can be an issue for patients with chronic renal disease or contrast allergies. Also, technical expertize is essential, as the timing of the scan must be optimized for maximum contrast enhancement of the structure of interest as failure to properly address these structures may lead to unnecessary risk to the patient from radiation and contrast exposure with a low likelihood of answering the clinical question. Moreover, MSCT angiography requires ECG gating and irregular rhythms can make for challenging images [16].
3D post-contrast whole heart sequence
3D post-contrast whole heart technique is a keystone cardiac MRI technique in the evaluation of patients with CHD. The comprehensive assessment of the thoracic vasculature it presents is uniquely suited to give detailed morphological information in CHD. It offers significant advantages, no ionizing radiation; the ability to be run free-breathing; and higher signal-to-noise ratio and isotropic voxel resolution for multiplanar reformatting assessment. It is now frequently used and has a proven utility for diagnostic imaging in patients with CHD [17].
TWIST
TWIST is a technique that creates a sequential fast series of multiplanar images with a good spatial resolution during the passage of intravenous contrast medium. It generates a series of imaging datasets at different time points of the same intravenous contrast medium bolus (unenhanced, pulmonary venous, systemic arterial, early systemic venous, and late systemic venous) allowing comprehensive assessment of the arterial and venous evaluation of clinical service [18].
Our results agree with Huf et al. in 2020 that found TWIST although being a very fast sequence but still suffered from loss of signal, resulting in a low SNR as well as blurring of small vessels [19]. However, TWIST provides a rapid overview of the status and patency of vascular structures. With only small contrast material doses, TWIST may be utilized to detect intra- and extracardiac shunts, to evaluate dynamic vascular anatomy in thoracic vascular disease [18].
In contrast to our results, the results from Michael et al. in 2007 found that Glenn shunt patency was better using TWIST. However, the number of patients was only six patients which make the comparison very difficult [20].
To the best of our knowledge, no available published data regarding the assessment of Glenn shunt by 3D post-contrast whole heart sequence. However, results published in 2008 by Tomasian et al. demonstrated that 3D whole heart sequence is optimal for evaluating the SVC as compared with MR angiography [21].
Also, results from Sonavane et al. in 2015 confirmed that 3D whole heart images in the axial and coronal planes are useful in evaluating the SVC lumen and wall and adjacent mediastinal structures [22].
According to the obtained results, the accuracy of this sequence in the assessment of superior cavo-pulmonary anastomosis could be attained with the better spatial resolution of the 3D post-contrast whole heart in addition to the lack of need to trace the contrast and optimization of the imaging time.
To the best of our knowledge, our study is the first study to compare MSCT angiography with two cardiac MRI techniques TWIST and 3D post-contrast whole heart in the evaluation of superior cavo-pulmonary anastomosis and systemic veno–venous collaterals based on quantitative and qualitative assessment.
The limitations for this study were the relatively small number of subjects and therefore further studies with a large patient population are warranted. Additionally, the study was done in a single center.