[Indications for magnetic resonance imaging in Internal Medicine. When do we really need this technology?]. / Internistische Indikation zur Magnetresonanztomographie. Wann brauchen wir sie wirklich?

Due to further technical developments in recent years, magnet resonance imaging (MRI) is now recognized as one of the primary diagnostic imaging modalities in the field of Internal Medicine. This review describes relevant indications for MRI in the different subspecialties of Internal Medicine and compares the diagnostic yield of MRI to other established modalities such as computed tomography and ultrasound.

MRI planimetry for diagnosis and follow-up of valve area in mitral stenosis treated with valvuloplasty.

PURPOSE: We sought to determine whether noninvasive planimetry by magnetic resonance imaging (MRI) is suitably sensitive and reliable for visualizing the mitral valve area (MVA) and for detecting increases in the MVA after percutaneous balloon mitral valvuloplasty (PBMV). MATERIALS AND METHODS: In 8 patients with mitral valve stenosis, planimetry of the MVA was performed before and after PBMV with a 1.5 T MR scanner using a breath-hold balanced gradient echo sequence (True FISP). The data was compared to the echocardiographically determined MVA (ECHO-MVA) as well as to the invasively calculated MVA by the Gorlin formula at catheterization (CATH-MVA). RESULTS: PBMV was associated with an increase of 0.79 +/- 0.30 cm (2) in the MVA (Delta MRI-MVA). The correlation between Delta MRI-MVA and Delta CATH-MVA was 0.92 (p < 0.03) and that between Delta MRI-MVA and Delta ECHO-MVA was 0.90 (p < 0.04). The overall correlation between MRI-MVA and CATH-MVA was 0.95 (p < 0.0001) and that between MRI-MVA and ECHO-MVA was 0.98 (p < 0.0001). MRI-MVA slightly overestimated CATH-MVA by 8.0 % (1.64 +/- 0.45 vs. 1.51 +/- 0.49 cm (2), p < 0.01) and ECHO-MVA by 1.8 % (1.64 +/- 0.45 vs. 1.61 +/- 0.43 cm (2), n. s.). CONCLUSION: Magnetic resonance planimetry of the mitral valve orifice is a sensitive and reliable method for the noninvasive quantification of mitral stenosis and visualization of small relative changes in the MVA. This new method is therefore capable of diagnosing as well as following the course of mitral stenosis. It must be taken into consideration that planimetry by MRI slightly overestimates the MVA as compared to cardiac catheterization.

Quantification of left-to-right shunting in adult congenital heart disease: phase-contrast cine MRI compared with invasive oximetry.

Atrial septum defects (ASDs), ventricular septum defects (VSDs) and patent ductus arteriosus (PDA) are the most common adult congenital heart defects. The degree of left-to-right shunting as assessed by the ratio of flow in the pulmonary (Qp) and systemic circulation (Qs) is crucial in the management of these conditions. This study compared phase-contrast cine magnetic resonance imaging (PC-MRI), a non-invasive imaging technique, with invasive oximetry for the measurement of shunt volumes during cardiac catheterisation in adults with left-to-right shunting. Both invasive oximetry and shunt quantification by PC-MRI (1.5 T scanner; Sonata, Siemens Medical Solutions) were performed on 21 patients with left-to-right shunting (14 ASD, 5 VSD, 2 PDA) and data on Qp/Qs ratios and left-to-right shunt fraction compared. Mean Qp/Qs ratios assessed by PC-MRI and oximetry were 2.10+/-0.76 and 1.96+/-0.77, respectively (p = 0.37). Mean shunt fraction was 46.3+/-19.6% when calculated by PC-MRI and 42.3+/-20.1% when obtained by oximetry (p = 0.12). There was a strong correlation of Qp/Qs ratios and shunt fraction between both methods (r = 0.61, p < 0.01 and r = 0.84, p < 0.0001, respectively). The two methods had a good agreement according to Bland and Altman plots with a small but non-significant overestimation of Qp/Qs-ratios and shunt fraction by PC-MRI. On receiver operating characteristic analysis, the sensitivity and specificity of PC-MRI to detect an oximetry-derived Qp/Qs ratio of > or =1.5:1 were 93% and 100% at a PC-MRI threshold of a Qp/Qs ratio > or =1.75:1 (area under curve (AUC) = 0.99). Quantification of left-to-right shunting can be performed reliably and accurately by PC-MRI and the data obtained by this method correlate closely to those from invasive oximetry.

Unicuspid aortic valve disease: a magnetic resonance imaging study.

PURPOSE: Congenitally malformed aortic valves are a common finding in adults with aortic valve disease. Most of these patients have bicuspid aortic valve disease. Unicuspid aortic valve disease (UAV) is rare. The aim of our study was to describe valve morphology and the dimensions of the proximal aorta in a cohort of 12 patients with UAV in comparison to tricuspid aortic valve disease (TAV) using magnetic resonance imaging (MRI). MATERIALS AND METHODS/RESULTS: MRI studies were performed on a 1.5 T scanner in a total of 288 consecutive patients with aortic valve disease. 12 aortic valves were retrospectively classified as UAV. Annulus areas and dimensions of the thoracic aorta were retrospectively compared to a cohort of 103 patients with TAV. In UAV, valve morphology was unicuspid unicommissural with a posterior commissure in all patients. Mean annulus areas and mean diameters of the ascending aorta were significantly greater in UAV compared to TAV (12.6 +/- 4.7 cm (2) vs. 8.7 +/- 2.3 cm (2), p < 0.01 and 4.6 +/- 0.7 cm vs. 3.6 +/- 0.5 cm, p < 0.0001, respectively), while no differences were observed in the mean diameters of the aortic arch (2.3 +/- 0.6 cm vs. 2.3 +/- 0.4 cm, p = 0.69). The diameters of the descending aorta were slightly smaller in UAV compared to TAV (2.2 +/- 0.5 cm vs. 2.6 +/- 0.3 cm, p < 0.05). CONCLUSION: In UAV, visualization of valve morphology by MRI is possible with good image quality. Valve morphology was classified as unicuspid unicommissural in all UAV patients. Dilatation of the proximal aorta > 4.5 cm is a frequent finding in UAV. Additional assessment of aortic dimensions is therefore recommended in patients with UAV.

Assessment of the anatomic regurgitant orifice in aortic regurgitation: a clinical magnetic resonance imaging study.

BACKGROUND: The aim of our study was to determine whether planimetry of the anatomic regurgitant orifice (ARO) in patients with aortic regurgitation (AR) by magnetic resonance imaging (MRI) is feasible and whether ARO by MRI correlates with the severity of AR. METHODS AND RESULTS: Planimetry of ARO by MRI was performed on a clinical magnetic resonance system (1.5 T Sonata, Siemens Medical Solutions) in 45 patients and correlated with the regurgitant fraction (RgF) and regurgitant volume (RgV) determined by MRI phase velocity mapping (PVM; MRI-RgF, MRI-RgV, n = 45) and with invasively quantified AR by supravalvular aortography (n = 32) and RgF upon cardiac catheterisation (CATH-RgF, n = 15). Determination of ARO was possible in 98% (44/45) of the patients with adequate image quality. MRI-RgF and CATH-RgF were modestly correlated (n = 15, r = 0.71, p<0.01). ARO was closely correlated with MRI-RgF (n = 44, r = 0.88, p<0.001) and was modestly correlated with CATH-RgF (n = 14, r = 0.66, p = 0.01). Sensitivity and specificity of ARO to detect moderately severe and severe aortic regurgitation (defined as MRI-RgF > or =40%) were 96% and 95% at a threshold of 0.28 cm2 (AUC = 0.99). Of note, sensitivity and specificity of ARO to detect moderately severe and severe AR at catheterisation (defined as CATH-RgF > or =40% or supravalvular aortography > or =3+) were 90% and 91% at a similar threshold of 0.28 cm2 (AUC = 0.95). Lastly, sensitivity and specificity of ARO to detect severe aortic regurgitation (defined as MRI-RgF > or =50% and/or regurgitant volume > or =60 ml) were 83% and 97% at a threshold of 0.48 cm2 (AUC = 0.97). CONCLUSIONS: Visualisation and planimetry of the ARO in patients with AR are feasible by MRI. There is a strong correlation of ARO with RgV and RgF assessed by PVM and with invasively graded AR at catheterisation. Therefore, determination of ARO by MRI is a new non-invasive measure for assessing the severity of AR.

Delayed hyperenhancement in magnetic resonance imaging of left ventricular hypertrophy caused by aortic stenosis and hypertrophic cardiomyopathy: visualisation of focal fibrosis.

OBJECTIVE: To compare the extent and distribution of focal fibrosis by gadolinium contrast-enhanced magnetic resonance imaging (MRI; delayed hyperenhancement) in severe left ventricular (LV) hypertrophy in patients with pressure overload caused by aortic stenosis (AS) and with genetically determined hypertrophic cardiomyopathy (HCM). METHODS: 44 patients with symptomatic valvular AS (n = 22) and HCM (n = 22) were studied. Cine images were acquired with fast imaging with steady-state precession (trueFISP) on a 1.5 T scanner (Sonata, Siemens Medical Solutions). Gadolinium contrast-enhanced MRI was performed with a segmented inversion-recovery sequence. The location, extent and enhancement pattern of hyperenhanced myocardium was analysed in a 12-segment model. RESULTS: Mean LV mass was 238.6 (SD 75.3) g in AS and 205.4 (SD 80.5) g in HCM (p = 0.17). Hyperenhancement was observed in 27% of patients with AS and in 73% of patients with HCM (p < 0.01). In AS, hyperenhancement was observed in 60% of patients with a maximum diastolic wall thickness >or= 18 mm, whereas no patient with a maximum diastolic wall thickness < 18 mm had hyperenhancement (p < 0.05). Patients with hyperenhancement had more severe AS than patients without hyperenhancement (aortic valve area 0.80 (0.09) cm(2)v 0.99 (0.3) cm(2), p < 0.05; maximum gradient 98 (22) mm Hg v 74 (24) mm Hg, p < 0.05). In HCM, hyperenhancement was predominant in the anteroseptal regions and patients with hyperenhancement had higher end diastolic (125.4 (36.9) ml v 98.8 (16.9) ml, p < 0.05) and end systolic volumes (38.9 (18.2) ml v 25.2 (1.7) ml, p < 0.05). The volume of hyperenhancement (percentage of total LV myocardium), where present, was lower in AS than in HCM (4.3 (1.9)% v 8.6 (7.4)%, p< 0.05). Hyperenhancement was observed in 4.5 (3.1) and 4.6 (2.7) segments in AS and HCM, respectively (p = 0.93), and the enhancement pattern was mostly patchy with multiple foci. CONCLUSIONS: Focal scarring can be observed in severe LV hypertrophy caused by AS and HCM, and correlates with the severity of LV remodelling. However, focal scarring is significantly less prevalent in adaptive LV hypertrophy caused by AS than in genetically determined HCM.

Mechanisms of regional wall motion abnormalities in contrast-enhanced dobutamine stress echocardiography.

BACKGROUND: In the diagnosis of coronary artery disease (CAD) with Dobutamine Stress Echocardiography (DSE), regional wall motion abnormalities (RWMA) are assumed to indicate a perfusion deficit. METHODS AND RESULTS: For a more particular examination of RWMAs, we compared simultaneous echo-contrast (Optisone)-enhanced DSE (0-40 microg/kg Dobutamine, 16-segment- model) and MiBi-SPECT in a prospective double-blinded study design in 69 non-selected consecutive patients (44 male, 25 female, age 64+/-12 years). Additionally, all patients were examined by coronary-angiography. The prevalence of significant CAD (stenosis >50% lumen diameter) was 52%. DSE had a sensitivity of 78% and a specificity of 66% for the detection of significant CAD with a positive and negative predictive value of 72 and 73%, respectively. Among 28 patients with significant CAD and positive DSE study (true positive), 78% displayed a corresponding perfusion deficit in MiBi-SPECT. Among 11 patients with a positive DSE study but no current significant coronary stenosis (false positive), 82% showed stress-induced RWMAs in the inferior/posterior region, 73% displayed left ventricular hypertrophy, 54% resting-ECG abnormalities and 45% resting-RWMA (3 previous MI, 2 previous CABG surgery). Among 8 patients with negative DSE study but significant coronary stenosis (false negative), 75% had a stenosis of the LCX, 63% displayed resting- WMA, 63% displayed left bundle branch block or ST-segment depression, 50% displayed only peripheral coronary stenosis, and DSE visualization was suboptimal in 38%. CONCLUSION: This prospective study in non-selected patients shows that the majority of RWMAs in DSE are matched to a perfusion deficit detectable by nuclear imaging. Nevertheless, pre-existing cardiac abnormalities may also lead to stress-induced RWMA not associated with a perfusion deficit or mask a perfusion deficit upon DSE. Particularly in patients with LV hypertrophy, resting-RWMA, bundle branch block or ST segment depression, the predictive value of DSE may, therefore, be limited.