Visualization of the pulmonary valve using cine MR imaging

PURPOSE: To evaluate the capability of bright-blood cine MR to directly visualize the leaflets of the valve replacement in pulmonary position following Ross operation. MATERIAL AND METHODS: Long and short axis views of the pulmonary valve were obtained in 10 normal subjects and 14 patients after Ross operation. Valve morphology and function were analyzed and signal-to-noise (SNR) and contrast-to-noise ratios (CNR) were calculated. Flow measurements were performed in the pulmonary trunk to assess pulmonary regurgitation. RESULTS: In all subjects, tricuspid morphology of the pulmonary valve was visualized. SNR of the leaflets in normal subjects (9.8 +/- 3.0) and in patients after Ross operation (7.5 +/- 2.2) differed significantly from blood (12.6 +/- 3.2 and 11.3 +/- 2.5, respectively, p < 0.05). Valvular regurgitation was seen in 5 patients as an insufficient closure of the valve which was confirmed by flow measurements. CONCLUSION: Cine MR enables in-plane visualization of the pulmonary valve and allows for functional and morphological evaluation in patients after pulmonary valve surgery.     

Pulmonary hypertension: pulmonary flow quantification and flow profile analysis with velocity-encoded cine MR imaging.

Velocity-encoded cine magnetic resonance (MR) imaging provides two-dimensional velocity maps of a cross-sectional area of a vessel. Pulmonary flow and flow patterns in the main pulmonary artery were analyzed with velocity-encoded cine MR imaging and Doppler echocardiography in 10 patients with pulmonary hypertension (PH), one patient with a dilated main pulmonary artery, and 10 healthy subjects, and these findings were compared. Peak systolic velocity measured with velocity-encoded cine MR imaging was similar to that measured with Doppler echocardiography in healthy subjects and in patients with PH. Velocity-encoded cine MR imaging demonstrated substantial differences in velocity across the vascular lumen in PH. The flow pattern in healthy subjects was different than that in patients with PH; the latter had lower peak systolic velocity and greater retrograde flow after middle to late systole. The retrograde flow observed in patients with PH reflected hemodynamic events, since it was inversely proportional to pulmonary flow volume and directly proportional to pulmonary resistance and cross-sectional area of the vessel. Velocity-encoded cine MR imaging demonstrates an inhomogeneous flow profile in PH and may serve as a noninvasive method to estimate pulmonary vascular resistance.     

Pulmonary arterial hypertension: noninvasive detection with phase-contrast MR imaging

PURPOSE: To retrospectively identify pulmonary arterial (PA) flow parameters measured with phase-contrast magnetic resonance (MR) imaging that allow noninvasive diagnosis of chronic PA hypertension (PAH). MATERIALS AND METHODS: The study was HIPAA compliant and was approved by the institutional review board; a waiver of informed consent was obtained. Fifty-nine patients (49 female patients; mean age, 46 years; range, 16-85 years) known to have or suspected of having PAH underwent breath-hold phase-contrast MR imaging and right-sided heart catheterization (RHC). The presence of PAH (mean pulmonary artery pressure [mPAP], >25 mm Hg) was confirmed in 42 patients. Parameters, including PA areas, PA strain, average velocity, peak velocity, acceleration time, and ejection time, were measured in each patient by investigators blinded to RHC results. These measurements were correlated with mPAP, systolic pulmonary artery pressure (sPAP), and pulmonary vascular resistance index (PVRI). The diagnostic ability of phase-contrast MR imaging to depict PAH was quantified. Statistical tests included Spearman rho coefficients, receiver operating characteristic curve analysis, and Bland-Altman plots. RESULTS: Results showed average velocity to have the best correlation with mPAP, sPAP, and PVRI (r = -0.73, -0.76, and -0.86, respectively; P < .001). Average velocity (cutoff value = 11.7 cm/sec) revealed PAH with a sensitivity of 92.9% (39 of 42) and a specificity of 82.4% (14 of 17). Sensitivity and specificity for the minimum PA area (cutoff value = 6.6 cm(2)) were 92.9% (39 of 42) and 88.2% (15 of 17), respectively. CONCLUSION: The average blood velocity throughout the cardiac cycle is strongly correlated with pulmonary pressures and resistance.     

Temporal correlation-based dynamic contrast-enhanced MR imaging improves assessment of complex pulmonary circulation in congenital heart disease.

A temporal correlation (TC) mapping method is proposed to help bolus chasing during dynamic contrast-enhanced (DCE) MRI of complex pulmonary circulation (CPC) in patients with congenital heart disease. DCE-MRI was performed on five healthy male subjects (23-24 years old) and 25 patients (nine males and 16 females, 0.25-44 years old), and TC maps were generated by performing pixel-based computation of cross-correlations to the pulmonary artery with a series of time shifts in all subjects. Qualitative and quantitative evaluations were performed in comparison with original DCE images. TC maps exhibited a better signal-to-noise ratio (SNR) by factors of 4.3 and 1.3 in the lung parenchyma, pulmonary veins, and superior artery/vein; a better intraparenchymal contrast-to-noise ratio (CNR) by factors of 1.5-5.4; and a significantly higher conspicuity in all regions except the pulmonary arteries when graded with a five-point score. TC maps evaluated by two experienced clinicians significantly added relevant information (P<0.001), and in some cases affected the final diagnosis. We conclude that TC maps facilitate bolus chasing for DCE-MRI by reducing recirculation effects and interframe fluctuations, and hence complements morphological imaging of CPC in patients with complex congenital heart disease.     

Global left ventricular perfusion: noninvasive measurement with cine MR imaging and phase velocity mapping of coronary venous outflow.

Velocity and volumetric flow of left ventricular venous outflow in the distal coronary sinus were measured with magnetic resonance (MR) velocity mapping techniques in 24 healthy men. A total of 16-21 velocity maps were acquired throughout the cardiac cycle. To determine the accuracy of the MR velocity-mapping pulse sequence, measurements were obtained with a flow phantom. Mean blood flow was 144 mL/min +/- 62 (standard deviation); mean velocity, 2.1 cm/sec +/- 1.0; and mean cross-sectional area, 1.2 cm2. Phasic measurements revealed a biphasic flow pattern in the coronary sinus, with a first peak in systole (257 mL/min +/- 174) and a second peak in early diastole (1,090 mL/min +/- 487). The cross-sectional area varied between 0.5 cm2 +/- 0.2 at end diastole and 1.9 cm2 +/- 0.6 in systole, a finding that suggests a capacitance function for venous outflow. Mean blood flow measurements were in agreement with measurements obtained invasively in previous studies. It is concluded that MR velocity mapping can enable noninvasive measurement of coronary venous outflow and global left ventricular perfusion and may become clinically useful in assessment of coronary blood flow reserve.     

"Pseudocoarctation" of the aorta: pitfall on cine MR imaging

The diagnosis of coarctation of the aorta on cine magnetic resonance imaging is based upon observation of localized narrowing in the region of the aortic isthmus with jet-like signal void areas extending distally. We observed similar findings in 8 of 20 (40%) normal volunteers examined in the sagittal oblique view. These artifactual findings relate primarily to out-of-plane motion of the thoracic aorta during a portion of the cardiac cycle, leading to partial volume averaging with pulmonary air. Awareness of this pitfall will prevent misdiagnosis of aortic coarctation in normal subjects and allow for more accurate assessment of severity of true coarctation.     

MR imaging of the pancreas: a practical approach

This article reviews the current practical MRI techniques in assessment of the pancreas. With the comprehensive "one-stop-shopping" approach, the great majority of pancreatic diseases can be detected and characterized by the use of a combination of T1, T2-weighted, MRCP, and fat-suppressed T1-weighted dynamic post-gadolinium SGE sequences. This approach may provide the clinician with information regarding the site, nature, and staging of pancreatic tumor in a single setting. In many institutions worldwide, however, including our own, CT remains the main imaging method for the assessment of acute pancreatic diseases, due largely to its wide availability. MR imaging is reserved for the indications listed above, most importantly, the detection of small and non-organ-deforming pancreatic ductal adenocarcinoma, islet cell tumors, choledocholithiasis and pancreatic duct calculi, cholangiocarcinomas, and in cases of pancreatic head enlargement with no mass discernable on CT.     

Quantification of regional pulmonary flow with 9mTc-MAA SPECT and cine phase contrast MR imaging

The purpose of this study was to evaluate the relationship between left and right pulmonary arterial flow measured by cine phase contrast magnetic resonance imaging (cine PCMRI) and the distribution of perfusion on 99mTc-MAA SPECT and to determine whether the regional pulmonary flow quantification was feasible with the combined use of these techniques. Twenty patients with different pulmonary diseases were evaluated. Left and right lung counts on 99mTc-MAA SPECT images were separately summed and the left-to-total count ratio was calculated. The left-to-total pulmonary flow ratio was calculated from the left and right main pulmonary flows measured with cine PCMRI. We evaluated the correlation and agreement between the ratio determined with 99mTc-MAA SPECT and cine PCMRI by linear regression analysis and Bland-Altman analysis. The left-to-total ratios obtained by 99mTc-MAA and cine PCMRI were 52.0 +/- 22.1% and 52.2 +/- 20.8%, respectively, and showed a strong correlation (r = 0.99, p < 0.001). The mean difference between the two methods in the ratio was 0.25 +/- 2.3% with a 95% confidence interval from -0.84 to 1.34. The results showed that the regional pulmonary flow was calculated with both the left and right pulmonary flow measured with cine PCMRI and the ratio of regional distribution on 99Tc-MAA SPECT images.     

Validation of cine phase-contrast MR imaging for motion analysis

The accuracy of cine phase-contrast magnetic resonance (MR) imaging for motion analysis was evaluated. By using a rotating phantom and postprocessing algorithm for phase tracking, errors arising during data acquisition were identified and compensation methods were developed. A spatially varying background phase offset in the velocity images was found to be due to eddy current-induced fields. The magnitude of the offset was in the range of 0–20 cm/sec, which is of the same order of magnitude as cardiac contractile velocities. Background offset is thus an important source of error in tracking cardiac motion. Study of different tracking algorithms revealed the need for an integration scheme using motion terms higher than velocity. Also, considerable improvement in the accuracy and stability of the predicted trajectories was obtained by averaging the trajectories proceeding both forward and backward in time from the starting point. With the algorithm developed, the motion of the phantom was tracked through a complete rotation of the phantom to an accuracy of 2 pixels.     

Solitary pulmonary nodules: a comparative study evaluated with contrast-enhanced dynamic MR imaging and CT

OBJECTIVE: The aim of this prospective study was to compare the diagnostic performances of dynamic MR imaging and CT for the differentiation of benign and malignant solitary pulmonary nodules (SPNs). METHODS: Eighty-one patients with SPNs (32 malignant, 49 benign) underwent dynamic MR imaging (n=31), dynamic CT (n=27), or both (n=23). The degree of peak enhancement of benign and malignant SPNs was compared on both dynamic MR imaging and CT. Receiver operating characteristic (ROC) analysis was performed to compare the diagnostic performances of dynamic MR imaging and CT. RESULTS: The malignant SPNs revealed significantly greater degrees of peak enhancement on dynamic MR imaging (mean +/- SD [p%SI] 131.2 +/- 46.1 versus 54.2 +/- 45.3; range [p%SI] 82.6-260.0 versus -0.7-171.7; P <0.0001) and CT (mean +/- SD [DMI] 37.8 +/- 15.1 versus 17.9 +/- 21.8; range [DMI] 14.1-68.2 versus -5.4-107.6; P=0.0004). Although dynamic MR imaging was somewhat superior to dynamic CT, the diagnostic performances of the 2 modalities based on ROC analysis were not statistically significant. CONCLUSIONS: Dynamic MR imaging and CT seem to be equally well suited for the differentiation between benign and malignant SPNs.     

Evaluation of aortic distensibility using cine MR imaging]

Regional aortic distensibility was measured noninvasively using cine MR imaging to determine whether it correlates with aging or risk of coronary artery disease (CAD). Twenty-two patients with CAD confirmed by angiography and 33 without CAD underwent cine MR imaging. Thirty-two sequential images were obtained in one cardiac cycle. The cross sectional area of the descending thoracic aorta was measured on both diastolic (A) and systolic (A') images. Aortic distensibility (A.D.) was calculated from the following equation: A.D. = (A'-A)/A/delta P. (delta P represents pulse pressure). Results of a simple regression analysis showed that decreased regional aortic distensibility was significantly correlated with the age of the patients (r = -0.762, p less than 0.005). In addition, the parameter was lower in patients with CAD than those without CAD (p less than 0.05). In conclusion, regional aortic distensibility derived from cine MR imaging is a useful parameter to evaluate not only aging but also pathological atherosclerosis of the aorta. In addition, this parameter might have some potential to evaluate the prediction of CAD in patients with normal serum cholesterol.     

Brain parenchyma motion: measurement with cine echo-planar MR imaging.

With echo-planar magnetic resonance (MR) imaging, the authors measured the intrinsic pulsatile motion of brain parenchyma. Phase-sensitive, electrocardiography-gated, two-dimensional cine images were acquired throughout the cardiac cycle by using a spin-echo, blipped echo-planar MR pulse sequence. Transverse and coronal planes were obtained in 14 healthy volunteers. Corrections were made for gross head motion. Brain motion consisted of a rapid displacement in systole, with a slow diastolic recovery. The motion occurred chiefly in the cephalocaudal and lateral directions; the anteroposterior motions were relatively small. Cephalocaudal velocities increase with proximity to the foramen magnum. The lateral motion is mainly a compressive motion of the thalami. Brain parenchymal velocities were as high as 2 mm/sec caudally in the brain stem and 1.5 mm/sec medially in the thalami. Net parenchymal excursions were at most 0.5 mm. Phase-based echo-planar velocity measurements agreed well with echo-planar Fourier velocity zeugmatography measurements and were consistent with reported values. Velocity mapping with echo-planar imaging offers a rapid and flexible method of assessing the pulsation velocities of the human brain.     

MR imaging: vascular anatomy of the abdomen

In support of the thesis that MRI may replace more invasive angiography in some applications, a total of 28 MR sections are presented to illustrate the vascular anatomy of the abdomen in coronal, transverse and sagittal planes. More than 20 vessels are identified ranging in size from the aorta to the left inferior adrenal vein and the spermatic veins. There is no anatomic continuity in sections made in the coronal and transverse planes; sequential sections of a single patient are presented in sagittal and parasagittal planes, however. The polarity of the images is reversed for ease of comparison with angiograms.     

Hepatic tumors: dynamic MR imaging

Thirty-six patients with hepatic tumors (28 hepatocellular carcinomas, seven cavernous hemangiomas, one metastatic tumor) were examined with serial magnetic resonance (MR) imaging, after a bolus intravenous injection of 0.05 mmol/kg gadolinium-diethylenetriaminepentaacetic acid. A typical MR imaging pattern for hemangiomas (present in five of seven cases [71.4%]) was a lesion of diminished signal intensity on precontrast images, peripheral contrast enhancement during the bolus dynamic phase, and complete fill-in of high signal intensity on delayed scan images. Twenty-eight hepatocellular carcinomas showed a variety of contrast enhancement patterns during the dynamic phase. In 21 patients (75%), there was no area of high signal intensity within the tumor on the delayed phase. A peripheral halo with delayed enhancement was noticed in 12 patients (42.8%) Histologic correlation in hepatocellular carcinomas showed that the degree of contrast enhancement corresponded to tumor vascularity and that the peripheral halo corresponded to fibrous capsular structure.     

Valvular regurgitation: dynamic MR imaging

Cine magnetic resonance (MR) imaging is a new technique that combines short repetition times, limited flip angles, gradient refocused echoes, and cardiac gating. This technique has a temporal resolution of up to 32 time frames per cardiac cycle and accentuates signal from flowing blood. Cine MR images of 56 valves in 27 patients were evaluated and compared with either Doppler echocardiograms or cardiac catheterization images. An area of decreased signal that correlated spatially and temporally with regurgitant blood flow was seen in all instances in which valvular incompetence was demonstrated on either Doppler echocardiograms or cardiac catheterization images (20 valves). This abnormality was seen in nine of 36 cases without valvular incompetence. Cine MR imaging may be sensitive to turbulence and thus sensitive to valvular regurgitation.