Determination of the Pressure Gradient in Children with Coarctation of the Aorta by Low-Field Magnetic Resonance Imaging

Abstract

During the past few years magnetic resonance imaging (MRI) has gained increasing importance in the noninvasive examination of congenital heart defects. Practically all existing examinations have been carried out with a magnetic field strength exceeding 1 (T high-field MRI). Flow quantification is considered to be an advanced MRI application and, in the past, has been available for high-field systems only. Therefore until recently, functional examinations such as MRI tomographic flow quantification were reported exclusively for high-field MRI units. From December 1998 to December 1999, nine patients (five girls and four boys, mean age 130 plus minus 3.6 months, range 62-185 months) were investigated by means of MRI after a previous surgical repair or interventional balloon dilatation of a coarctation of the aorta (mean postinterventional time period 23 plus minus 0.4 months). The examination was carried out without sedation in an open low-field unit (Siemens Magnetom Open 0.2 T). Cardiac-triggered spin-echo sequences were used with a 3-mm to 7-mm slice thickness in an axial and a double oblique plane. The measurement of the immediate poststenotic flow velocity was done by flow-sensitive sequences developed for the study (phase-sensitive flow measurement sequences: TE, 6-12 msec; TR, 50 msec; flip angle, 60 degrees; Vmax, 200-1200 cm/sec; two acquisitions). All patients were examined on the same day with comparative echocardiographic procedures. In all cases, an excellent anatomical evaluation of the aortic arch was possible. The diameters of the residual stenosis were measured by MRI and correlated well r = 0.95; p ? 0.001; mean difference 0.44 +/- 2.47 mm) with echocardiographic results. No wall damage was observed in any of the cases studied. The pressure gradient of the stenosis calculated from the flow sequence was between 17 and 50 mmHg and corresponded well (r = 0.93; p = 0.001; mean difference 0.67 +/- 11 mmHg) with the results obtained from echocardiography. The study demonstrates that examination of the aortic arch is possible in a low-field MRI system, with its significant advantages (lower patient discomfort and more cost-effective examination). In addition, a quantitative flow measurement in low-field MRI was realized for the first time. Low-field MRI therefore seems to be a good, noninvasive method for examining patients with a poor echocardiographic representation of the aortic arch.

Magnetic Resonance Imaging Predictors of Coarctation Severity

“…A practical advantage of these findings is that both 3D MRA of the thoracic aorta and PVC-MRI flow analysis are established MRI techniques, are commonly used in clinical practice, and require relatively short acquisition and imageprocessing times. 9,[13][14][15][16][23][24][25][26] Moreover, both techniques have been evaluated in patients with CoA and were found to reliably assess aortic morphology and collateral vessels and to accurately quantify flow in the descending aorta. 9,13 Assessment of coarctation severity presents a clinical challenge.…”

Magnetic Resonance Imaging–Guided Balloon Angioplasty of Coarctation of the Aorta

“…15,31 Assessment of pressure gradients across a vascular stenosis is limited when velocity-encoded cine MRI is used because of spin dephasing, which accompanies turbulent blood flow. 32 Quantification of collateral blood flow was proposed as an alternative method to determine the functional significance of a CoA 33,34 ; however, there is no knowledge of the degree to which collateral blood flow diminishes immediately after intervention. Therefore, we relied on invasive pressure measurements to determine the success of the interventional procedure.…”

Simple Congenital Heart Lesions

“…In a retrospective study of 84 adult patients following intervention for coarctation of the aorta, Therrien and colleagues showed that the combination of clinical assessment and CMR on every patient was more "cost-effective" for detecting complications than combinations that relied on echocardiography or chest radiography as imaging modalities (41). Other studies have shown the utility of CMR in infants and children with coarctation and other anomalies of the aortic arch (42)(43)(44). Computer tomography can also provide excellent anatomic imaging of the aorta but little functional information regarding the left ventricle or pressure gradient across any obstruction.…”