Postoperative evaluation of pulmonary arteries in congenital heart surgery by magnetic resonance imaging: comparison with echocardiography

Which cardiovascular magnetic resonance planes and sequences provide accurate measurements of branch pulmonary artery size in children with right ventricular outflow tract obstruction?

Children with right ventricular outflow tract obstructive (RVOTO) lesions require precise quantification of pulmonary artery (PA) size for proper management of branch PA stenosis. We aimed to determine which cardiovascular magnetic resonance (CMR) sequences and planes correlated best with cardiac catheterization and surgical measurements of branch PA size. Fifty-five children with RVOTO lesions and biventricular circulation underwent CMR prior to; either cardiac catheterization (n = 30) or surgery (n = 25) within a 6 month time frame. CMR sequences included axial black blood, axial, coronal oblique and sagittal oblique cine balanced steady-state free precession (bSSFP), and contrast-enhanced magnetic resonance angiography (MRA) with multiplanar reformatting in axial, coronal oblique, sagittal oblique, and cross-sectional planes. Maximal branch PA and stenosis (if present) diameter were measured. Comparisons of PA size on CMR were made to reference methods: (1) catheterization measurements performed in the anteroposterior plane at maximal expansion, and (2) surgical measurement obtained from a maximal diameter sound which could pass through the lumen. The mean differences (Δ) and intra class correlation (ICC) were used to determine agreement between different modalities. CMR branch PA measurements were compared to the corresponding cardiac catheterization measurements in 30 children (7.6 ± 5.6 years). Reformatted MRA showed better agreement for branch PA measurement (ICC > 0.8) than black blood (ICC 0.4-0.6) and cine sequences (ICC 0.6-0.8). Coronal oblique MRA and maximal cross sectional MRA provided the best correlation of right PA (RPA) size with ICC of 0.9 (Δ -0.1 ± 2.1 mm and Δ 0.5 ± 2.1 mm). Maximal cross sectional MRA and sagittal oblique MRA provided the best correlate of left PA (LPA) size (Δ 0.1 ± 2.4 and Δ -0.7 ± 2.4 mm). For stenoses, the best correlations were from coronal oblique MRA of right pulmonary artery (RPA) (Δ -0.2 ± 0.8 mm, ICC 0.9) and sagittal oblique MRA of left pulmonary artery (LPA) (Δ 0.2 ± 1.1 mm, ICC 0.9). CMR PA measurements were compared to surgical measurements in 25 children (5.4 ± 4.8 years). All MRI sequences demonstrated good agreement (ICC > 0.8) with the best (ICC 0.9) from axial cine bSSFP for both RPA and LPA. Maximal cross sectional and angulated oblique reformatted MRA provide the best correlation to catheterization for measurement of branch PA's and stenosis diameter. This is likely due to similar angiographic methods based on reformatting techniques that transect the central axis of the arteries. Axial cine bSSFP CMR was the best surgically measured correlate of PA branch size due to this being a measure of stretched diameter. Knowledge of these differences provides more precise PA measurements and may aid catheter or surgical interventions for RVOTO lesions.

Ascending Aortic and Main Pulmonary Artery Areas Derived From Cardiovascular Magnetic Resonance as Reference Values for Normal Subjects and Repaired Tetralogy of Fallot

Background—

Cardiac magnetic resonance (CMR) imaging is an important clinical tool for serial follow-up of patients with congenital heart disease, but normative data for great vessel dimensions in pediatric subjects are scarce. We investigated the ascending aortic (AO) and main pulmonary artery dimensions in normal children and young adults in comparison with a cohort of patients with repaired tetralogy of Fallot (TOF).

Methods and Results—

Subjects were prospectively enrolled for cardiac magnetic resonance after a standardized protocol in 14 participating centers of the German Competence Network for Congenital Heart Defects. All studies were performed in 1.5-T scanners and used single-slice multiphase acquisitions steady-state free precession and velocity-encoded cine. AO and main pulmonary artery areas were measured. The cohort consisted of 483 subjects: 105 normal controls (55 men; 50 women; and median age, 14 years) and 378 patients with repaired TOF (210 men; 168 women; and median age, 16 years). Among TOF, 35 (9%) had pulmonary atresia, 98 (26%) had a palliative procedure before repair, the mean age at repair was 2.9 years, and 82 (23%) used a transannular patch repair. Great vessel areas correlated well with body surface area and age in controls and reference Z-score values were derived. Z scores for ascending AO areas were larger in TOF compared with controls (mean Z score =1.95, P =0.001). In TOF, pulmonary atresia ( P =0.003), male sex ( P =0.01) and previous palliations ( P =0.046) were associated with larger AO areas. Main pulmonary artery area Z scores in surgically modified TOF were smaller on an average than controls (mean Z score =−0.293 P =0.001) but not small to the same extent as the AO was large.

Conclusions—

This study provides cardiac magnetic resonance reference Z scores for great vessel areas in normal children and adolescents in comparison with a large contemporary cohort of repaired TOF. Male sex, pulmonary atresia, and previous palliations emerged as predictors for larger AO dimensions in TOF.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00266188.

Cardiac MRI in Congenital Heart Disease - Our Experience

A significant recent advance that has occurred world over in the continuously evolving field of Magnetic Resonance Imaging (MRI) practice is the introduction of Cardiac applications. Cardiac MRI has moved to the centre stage of clinical management strategy by non-invasively imaging the structure as well as function of the heart. It has a wide range of specific applications such as delineation of morphological anatomy, quantification of flow and pressure across cardiac valve dysfunction, evaluation of myocardial function, assessment of infarcts, mapping coronary arteries and so on. Evaluation of congenital heart disease (CHD) is an important application of Cardiac MRI since the morphological details of chambers, septum, defects and anomalous connections are depicted accurately. Besides, flow information across valves, chambers, outflow tracts and shunts are also provided. This article describes our experience in the use of cardiac MRI in congenital heart disease.

Assessment of modified Blalock-Taussig shunt in children with congenital heart disease using multidetector-row computed tomography

The purpose of this study was to assess the feasibility of multidetector-row computed tomography (MDCT) for the evaluation of modified Blalock-Taussig (B-T) shunt in children with congenital heart disease associated with reduced pulmonary blood flow. A total of 25 consecutive patients (mean age, 2.6 ± 3.6 years; range, 2 months-16 years) underwent MDCT angiography of the thorax with a 16-detector row scanner prior to cardiac catheterization. A total of 39 shunts (right, 22; left, 17) were included in the study. Conventional angiographic findings were used as the gold standard for the detection of B-T shunts. Shunt diameter was measured quantitatively and independently at four sites (the subclavian artery site, the pulmonary artery site, the widest site, and the stenotic site) on MDCT and on conventional invasive angiography. All B-T shunts were depicted on multiplanar reconstruction (MPR), maximum intensity projection (MIP), curved planar reconstruction (CPR), and three-dimensional volume-rendered (VR) images, enabling evaluation in all patients except for one with occluded shunt. There were excellent correlations between MDCT- and conventional angiography-based measurements of shunt diameter at the subclavian artery site, pulmonary artery site, and the widest site (R² = 0.46, 0.74 and 0.64, respectively; p < 0.0001 for each), although systematic overestimation was observed for MDCT (mean percentage of overestimation, 23.1 ± 32.4%). Stenotic site diameter and degree of stenosis showed a mild correlation (R² = 010 and 0.25, respectively; p < 0.01 for each). This study demonstrates that MDCT is a promising tool for the detection of lesions in B-T shunts.

ACR appropriateness criteria on suspected congenital heart disease in adults

The number of adults with congenital heart disease is increasing in North America. This is attributable to a variety of factors, including improvements in surgical techniques and increases in immigration. Cardiac imaging is critical for the initial assessment of adults with newly suspected congenital heart disease as well as for the serial assessment of adults with known congenital heart disease. Chest radiography and echocardiography continue to be the initial tools used to evaluate adult congenital heart disease. However, cardiac computed tomography and magnetic resonance imaging have significantly improved over the years and have become integral to the evaluation of adult congenital heart disease, often precluding the necessity for invasive cardiac catheterization. Noninvasive imaging is particularly useful for the surveillance of patients with surgically corrected congenital heart disease, who often require 2 or more additional operations.

Disparity between ratios of diameters and blood flows in central pulmonary arteries in postoperative congenital heart disease using MRI

PURPOSE

To compare the relative severity of stenoses of right or left pulmonary arteries with differences in flow to each lung after repair of congenital heart disease (CHD).

MATERIALS AND METHODS

A total of 15 patients with postoperative congenital heart disease underwent MRI to evaluate branch pulmonary artery stenoses. Spin-echo images and MR angiography were used to assess morphology, and velocity-encoded cine (VEC) MRI was used to measure flow in the right and left pulmonary arteries. The ratios of the narrowest diameters of the right to left pulmonary arteries (R/L size) and right to left pulmonary arterial flow (R/L flow) were compared using Spearman's correlation. F test was used to assess the significance of the regression coefficients.

RESULTS

R/L size ratio varied from 0.50 to 2.66, while the R/L flow ratio varied from 0.36 to 12.02. There was an exponential relationship between R/L size and R/L flow, with r2=0.78 and P=0.001. However, severity of morphologic stenoses was not clinically useful for predicting flow reduction. Prediction residuals ranged from -136% to 54% of the true R/L flow.

CONCLUSION

Anatomical evaluation of the pulmonary arteries does not predict accurately differential blood flow in patients with pulmonary stenoses. Therefore, blood flow measurements are essential when considering the need for further surgical or interventional procedures.

Patency of cavopulmonary connection studied by single phase electron beam computed tomography

PURPOSE

The shunt patency and anatomic alteration of central PA after cavopulmonary connection was assessed by one phase electron-beam computed tomography (EBCT) METHODS: Thirteen patients that received a bi-directional cavo-pulmonary shunt (BCPS, n = 7) or total cavo-pulmonary connection (TCPC, n = 6) were included. The patency of the shunt and the anatomy of intra-pericardial PA were evaluated by EBCT, and compared by angiography and echocardiography.

RESULTS

EBCT accurately evaluated shunt patency and the anatomy of the intra-pericardial PA, except for the incorrect diagnosis of SVC-PA shunt patency and peripheral pulmonary stenosis in two TCPC patients. Both of these patients had bilateral SVC and received either bilateral BCPS or ligation of the left SVC respectively. The baffle between the IVC and PA was partly opacified through a fenestration of the baffle, but was not opacified in two patients without fenestration.

CONCLUSION

EBCT accurately evaluated shunt patency and the anatomy of central PA, however, the accuracy was limited in two cases with bilateral SVC. The opacification of the intra-atrial baffle was insufficient in TCPC cases. Multi-phase CT angiography may overcome this limitation in this patient subset.

Accuracy of MRI evaluation of pulmonary blood supply in patients with complex pulmonary stenosis or atresia

Detailed imaging of pulmonary artery (PA) anatomy and significant aorto-pulmonary collaterals (APCs) is crucial for surgical planning and follow-up in patients with complex congenital heart disease (CHD) and pulmonary stenosis or atresia. Because examination by echocardiography is often technically limited and catheterization is invasive, this study evaluated the diagnostic accuracy of magnetic resonance imaging (MRI) as an alternate non-invasive tool. Thirteen patients (median age 28 years, range: 1-44 years) underwent both cardiac catheterization and MRI within a median of two months (range 0.1-8 months). Diagnoses included tetralogy of Fallot (TOF) with pulmonary atresia (n = 8), TOF with pulmonary stenosis (n = 2), single left ventricle with pulmonary stenosis (n = 2), and complex heterotaxy with pulmonary stenosis (n = 1). The MRI sequences used in this study were ECG-gated spin echo and gradient echo sequences acquired in multiple planes. Compared to catheterization, MRI had 100% sensitivity and specificity for the diagnosis of main PA (n = 6) and branch PA (n = 13) hypoplasia or stenosis, as well as discontinuous (n = 4) or absent (n = 10) branch PAs. There was complete agreement between catheterization and MRI identification of significant APCs (n = 18). Main PA atresia was noted by MRI in four patients but was not definitively seen by catheterization in any. MRI but not catheterization precisely defined the distance between discontinuous PAs and their relationship to other mediastinal structures. In conclusion, cardiac MRI is a reliable non-invasive imaging modality to define PA and APC anatomy in patients with complex pulmonary stenosis or atresia.

Evaluation of pulmonary blood supply by multiplanar cine magnetic resonance imaging in patients with pulmonary atresia and severe pulmonary stenosis

The purpose of this study was to assess the capability of multiplanar cine magnetic resonance imaging (MRI) for evaluating pre- and post-operative pulmonary circulation in patients with pulmonary atresia and severe pulmonary stenosis. Seventy-three multiplanar cine MRIs were performed in 30 patients, aged 1 month to 7 years (mean age, 27 months). The morphology and size of the central pulmonary arteries (PA), source of the major aortopulmonary collateral arteries (MAPCA), patency of Blalock-Taussig (BT) shunt vessels, and the post-operative pulmonary circulation were assessed. The accuracy of cine MRI was compared with that of angiography in all patients. The PA was visualized to the first hilar branch in 21 patients, but not in 8 patients in whom the central PA was absent. On follow-up MRI, PA growth was measured, and the results showed excellent correlation with the results obtained by angiography. In 17 patients who had undergone 23 BT shunt operations, cine MRI correctly demonstrated all patient shunts and 5 of 6 stenotic lesions. Multiplanar cine MRI provided excellent detail of the peripheral PA in all patients, 7 of 8 peripheral pulmonary stenoses, 3 of 4 nonconfluent pulmonary arteries, and 2 of 3 PA obstructions. Although the sources of MAPCA were identified in 7 of 9 patients, the distal connection of the MAPCA was not detected in all patients. Seven patients were reexamined after pulmonary plasty; they exhibited normal pulmonary flow patterns. Multiplanar cine MRI provides high-resolution imaging of PA with dynamic visualization of flow and is an effective noninvasive technique for evaluating pre- and post-operative patients with pulmonary atresia and severe pulmonary stenosis.

MRI and echocardiography: how do they compare in adults?

TTE with color flow imaging remains the most appropriate initial method for imaging CHD in adults. In many patients with minor abnormalities, this will be the only imaging required. For complicated intracardiac anomalies not well shown by TTE, TEE or MRI are usually adequate with the choice of technique being dependent on the availability of appropriate equipment and expertise. For great vessel abnormalities, further evaluation with MRI and MRA is most appropriate. In patients suspected of having significant systemic or pulmonary venous abnormalities or abnormalities of the aortic arch, MRI and MRA should be regarded as the definitive imaging technique. MRI and MRA are robust methods for evaluating intracardiac disease and can provide accurate information on cardiac chamber anatomy relationships, valvar lesions, and shunts. However, in most patients, this information is provided more rapidly and cost effectively by color Doppler echocardiography.

MRI and echocardiography in children: how do they compare?

Clearly, both echocardiography and MRI play vital roles in the diagnosis and management of children with congenital heart defects. 2-D Doppler echocardiography is very easy to use in a vast array of clinical situations. The accuracy of the anatomic and hemodynamic findings are well accepted. In comparative studies, 2-D Doppler echocardiography appears preferable for intracardiac anatomy, whereas MRI appears preferable for extracardiac anatomy. In certain patients, Doppler echocardiography may not be able to optimally obtain the anatomic or hemodynamic information, and MRI should be used in these particular cases.

Magnetic resonance imaging of the cardiovascular system and airway

Cardiovascular MR imaging is unique in its ability to combine anatomic, physiologic, and functional information in a single examination. Established applications in the pediatric population include the evaluation of the child with a suspected thoracic aortic arch anomaly, vascular compression of the airway, coarctation of the aorta, pulmonary arterial and venous abnormalities, and cardiac or paracardiac masses. The increasing availability of radiologists with the knowledge and commitment to cardiac imaging will allow this exciting technique to thrive in the future, to the benefit of our patients.

MR imaging of surgical complications of systemic-to-pulmonary artery shunts

Patients with a systemic-to-pulmonary artery shunt and positive findings on traditional imaging modalities such as chest X-ray, echocardiography, or cardiac angiography often can benefit from additional noninvasive imaging with magnetic resonance imaging (MRI). Diagnostic dilemmas encountered include: pseudoaneurysms, contained fluid collection (seroma) surrounding a shunt, and stenosis of the shunt anastomoses. MRI studies using traditional cardiac-triggered spin-echo (SE) imaging and the newer breathhold MRI studies with k-space segmented gradient-recalled echo (GRE) imaging can greatly help resolve diagnostic dilemmas. By combining different MR imaging techniques it becomes possible to clearly distinguish between pseudoaneurysms and seroma, to exclude an active leak and to sometimes visualize the distal anastomosis with more precision than conventional angiography. MRI is often able to add information needed for clinical decision making prior to surgical repair.