Achim Seeger

A Comprehensive Approach to the Analysis of Contrast Enhanced Cardiac MR Images

Current magnetic resonance imaging (MRI) technology allows the determination of patient-individual coronary tree structure, detection of infarctions, and assessment of myocardial perfusion. Joint inspection of these three aspects yields valuable information for therapy planning, e.g., through classification of myocardium into healthy tissue, regions showing a reversible hypoperfusion, and infarction with additional information on the corresponding supplying artery. Standard imaging protocols normally provide image data with different orientations, resolutions and coverages for each of the three aspects, which makes a direct comparison of analysis results difficult. The purpose of this work is to develop methods for the alignment and combined analysis of these images. The proposed approach is applied to 21 datasets of healthy and diseased patients from the clinical routine. The evaluation shows that, despite limitations due to typical MRI artifacts, combined inspection is feasible and can yield clinically useful information.

Risk Stratification by Adenosine Stress Cardiac Magnetic Resonance in Patients With Coronary Artery Stenoses of Intermediate Angiographic Severity

OBJECTIVES The purpose of this study was to determine the role of adenosine stress cardiac magnetic resonance (CMR) for risk stratification in patients with coronary artery stenoses of intermediate angiographic severity. BACKGROUND Coronary angiography only provides a morphological description of coronary lesions. As the patients prognosis is closely related to the functional significance of angiographically detected coronary lesions, a functional assessment is desirable in patients with coronary artery stenoses of intermediate severity. METHODS Myocardial perfusion measurements at rest and adenosine stress were performed on 81 patients (75.6% male, mean age 64.2 years) with stable angina pectoris (AP) and coronary artery stenoses of intermediate angiographic severity (50% to 75%). Regardless of the CMR result, all patients were treated conservatively with an intensified medical treatment, and a follow-up was performed after 18 +/- 8 months and 30 +/- 8 months. The primary end point was defined as a major adverse cardiac event (MACE): all-cause death, stroke, acute coronary syndrome; the secondary end point was defined as target vessel revascularization. Furthermore, AP and dyspnea were evaluated. RESULTS After the follow-up period of 30 +/- 8 months, 9 patients with perfusion deficit (PD) suffered from MACE, whereas no MACE occurred among the 36 patients without PD (p = 0.014). Among patients who had MACE, the number of ischemic segments (2.3 +/- 1.6 vs. 1.4 +/- 1.6, p = 0.0025) was significantly higher, whereas the number of delayed enhancement segments did not differ (1.4 +/- 1.6 vs. 1.6 +/- 2.3, p = 0.4). Target vessel revascularization was required in 38% of patients with PD and 6% of patients without PD (p = 0.005). In addition, the percentage of freedom from AP and dyspnea at the follow-up after 18 +/- 8 months was significantly lower among patients without perfusion deficit (69.4% vs. 15.6%; p = 0.0001). After a follow-up period of 30 +/- 8 months, the rate of AP (11.1% vs. 8.3%, p = 0.33) as well as the percentage of patients free of symptoms was similar in both groups (77.8% vs. 88.9%, p = 0.82). CONCLUSIONS Adenosine stress CMR may help to identify patients at risk who benefit from intensified medical treatment and close follow-up.

Comparison of Three Different MR Perfusion Techniques and MR Spectroscopy for Multiparametric Assessment in Distinguishing Recurrent High-Grade Gliomas from Stable Disease

RATIONALE AND OBJECTIVES Magnetic resonance (MR) perfusion techniques and MR spectroscopy (MRS) provide specific physiological information that may allow distinction between recurrent glioma and progression from stable disease. MATERIALS AND METHODS Forty patients underwent conventional MR imaging, dynamic contrast-enhanced T1-weighted perfusion imaging, dynamic susceptibility contrast-enhanced perfusion imaging (DSC), and multivoxel MRS. Arterial spin labeling was available in 26 of these patients. Quantitative parameters were calculated in tumor recurrences and stable disease, which were retrospectively verified on clinical and radiological follow-up. Receiver operating characteristic curves for each parameter were generated for the differentiation between recurrent glioma and stable disease. A forward discriminant analysis was undertaken to assess the power of the conjunction of MR perfusion techniques and MRS. RESULTS Of the 40 patients, 23 were determined to have recurrent gliomas. Differences in arterial spin labeling between the two groups were not statistically significant (P = .063). Sensitivities and specificities for the detection of recurrent lesions in dynamic contrast-enhanced T1-weighted perfusion imaging and DSC were 61.9% and 80% transfer constant k(trans), 77.3% and 84.6% for cerebral blood flow, and 81% and 76.9% for cerebral blood volume, respectively. Among the parameters in MRS, the ratio of choline to normalized creatine showed the best diagnostic accuracy (P = .014; sensitivity 70%, specificity 78.6%). When considering all perfusion modalities, diagnostic accuracy could be increased to 82.5%, adding MRS to the multiparametric approach resulted in a diagnostic accuracy of 90.0%. CONCLUSIONS MR perfusion techniques and MRS are useful tools that enable improved differentiation between recurrent glioma and stable disease. Among the single parameters, DSC showed the best diagnostic performance. Multiparametric assessment substantially improved the ability to differentiate the two entities.

Assessment of left ventricular volumes and mass with fast 3D cine steady-state free precession k-t space broad-use linear acquisition speed-up technique (k-t BLAST)

To compare left ventricular (LV) volume and mass assessment using two‐dimensional (2D) cine steady‐state free precession (SSFP) and k‐t space broad‐use linear acquisition speed‐up technique (k‐t BLAST) accelerated 3D magnetic resonance imaging (MRI).

Ultrafast Whole-Body MR Angiography with Two-dimensional Parallel Imaging at 3.0 T: Feasibility Study

The study was approved by the local ethics committee, and informed consent was provided by all participants prior to the examination. The aim of the study was to assess the feasibility of whole-body three-dimensional (3D) contrast material-enhanced magnetic resonance (MR) angiography with parallel imaging in the phase- and section-encoding directions (ie, integrated parallel acquisition technique [iPAT(2); Siemens, Erlangen, Germany]) for all anatomic imaging stations in combination with a single injection of contrast material. Whole-body contrast-enhanced MR angiography was performed in 23 patients at 3.0 T. Images were evaluated by two independent observers for quality on a four-point scale (where a score of 1 indicated poor image quality and a score of 4, excellent image quality); signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) were calculated for representative vessel regions in each station. Mean image quality scores were 3.13 +/- 1.15 (standard deviation) and 3.17 +/- 1.14 for observers 1 and 2, respectively (kappa = 0.81). Signal intensity measurements revealed mean SNR values between 36.2 +/- 8.0 and 56.2 +/- 17.7 and mean CNR values between 29.0 +/- 7.4 and 48.2 +/- 15.7. The data suggest that contrast-enhanced MR angiography with iPAT(2) is feasible for whole-body applications and allows acquisition of 3D data sets with adequate spatial resolution within short measurement times, facilitating a single injection of contrast material.

Preoperative evaluation of potential living related kidney donors with high-spatial-resolution magnetic resonance (MR) angiography at 3 tesla comparison with intraoperative findings

Purpose:The purpose of this prospective study was to determine the feasibility and accuracy of high-spatial-resolution MR imaging at 3 Tesla (T) in the preoperative evaluation of potential living related kidney donors. Materials and Methods:Eighteen potential donors (8 men, 10 women; mean age, 50.1 ± 14.2 years) for renal transplantation were evaluated with 3 T MR imaging. A high-spatial-resolution 3-dimensional (3D) gradient-echo MR angiography (repetition time/echo time, 3.0/1.14 ms; flip, 19–23°; matrix, 512; slice thickness, 1.0 mm) using parallel acquisition technique (GRAPPA) with an acceleration factor of 3 was performed on a whole body scanner. Images were evaluated in a prospective and blinded fashion by 2 MR radiologists. The number of renal arteries, presence of early branches (defined as a branch arising within 2 cm of the main renal ostium), and renal artery stenosis were analyzed. The renal parenchyma, collecting system and ureters, were evaluated on the MR urograms. Interpretation of MR images were compared with surgical findings. Results:Based on MR angiography data sets, a total of 36 main and 9 accessory renal arteries was found. There were 5 renal arteries presenting an early branching (≤2 cm). The correct venous anatomy was identified in 13 of 14 patients (93%), including a single left renal vein anterior to the aorta (n = 3), retroaortic left renal vein (n = 2), and single right renal vein (n = 9). A single collecting system in all harvested kidneys was identified correctly with MR imaging. Overall, the sensitivity and positive predictive value of MRI in correctly determining the vascular and parenchymal anatomy in the harvested kidney was 85% and 93%, respectively. Conclusions:High-spatial-resolution contrast-enhanced MR angiography at 3 T can predict successful donor nephrectomy in potential living related kidney donors.

Impact of restrictive physiology on intrinsic diastolic right ventricular function and lusitropy in children and adolescents after repair of tetralogy of Fallot

Background Restrictive right ventricular (RV) physiology is a phenomenon considered potentially beneficial when detected in children and adolescents with repaired tetralogy of Fallot (ToF). It is typically characterised by antegrade flow in the pulmonary artery in late diastole at the time of atrial contraction. However, little is known about the impact of restrictive physiology on intrinsic diastolic RV function or lusitropy. Methods Diastolic function was prospectively assessed at baseline level and during dobutamine infusion using the pressure–volume conductance system. End diastolic forward flow in the pulmonary artery was measured by MRI. Results Twenty-five patients aged 17.9±7.5 years were studied. Although the end diastolic RV pressure, the time constant of isovolumic RV relaxation (τ) and dP/dtmin were similar between both groups, the slope of the end diastolic pressure–volume relationship (Eed) was significantly higher in the restrictive group indicating increased diastolic stiffness in these patients (0.14±0.05 vs 0.06±0.01, p=0.03). Dobutamine stress, however, led to an increase in Eed in the entire ToF cohort indicating an abnormal diastolic response to catecholamines in these patients. Conclusions Diastolic RV stiffness of repaired ToF patients with restrictive physiology is increased. The lusitropic response of the RV to β adrenergic agents is abnormal after ToF repair regardless of whether restrictive physiology is present or not. This has potential implications, particularly for postoperative drug management.

Isotropic High-Spatial-Resolution Contrast-enhanced 3.0-T MR Angiography in Patients Suspected of Having Renal Artery Stenosis

The purpose of this study was to prospectively evaluate the diagnostic performance of contrast material-enhanced magnetic resonance (MR) angiography performed at 3 T for assessment of renal artery stenosis (RAS) by using parallel acquisition techniques with high acceleration factors and with digital subtraction angiography (DSA) as the reference standard. The study was institutional review board approved, and written informed consent was obtained from all patients. Twenty-nine patients (18 men, 11 women; mean age, 57.1 years +/- 14.3 [standard deviation]) suspected of having RAS underwent MR angiography. Images were evaluated qualitatively and quantitatively. The interobserver variability, sensitivity, specificity, and positive and negative predictive values of 3-T MR angiography, as compared with DSA (performed in 15 patients), were calculated. All examinations yielded good or excellent image quality. The sensitivity and specificity of MR angiography in grading significant (>75%) stenosis were 94% and 96%, respectively. Owing to its high sensitivity, contrast-enhanced 3-T MR angiography can be used reliably to exclude RAS and can serve as a useful screening method in the diagnostic work-up of patients with arterial hypertension.

Pretreatment Evaluation of Peripheral Vascular Malformations Using Low-Dose Contrast-Enhanced Time-Resolved 3D MR Angiography: Initial Results in 22 Patients

OBJECTIVE The objective of our study was to assess the feasibility and diagnostic performance of time-resolved MR angiography (MRA) in the pretreatment evaluation of peripheral vascular malformations at 1.5 T. SUBJECTS AND METHODS Twenty-two consecutive patients (15 women and seven men; mean age, 22.1 ± 12.1 years) who were known or suspected to have vascular malformations were studied using time-resolved MRA with interleaved stochastic trajectories and parallel acquisition followed by conventional MRA (n = 12). All studies were performed on a 1.5-T whole-body MR system. Image sets of time-resolved and conventional MRA were independently reviewed by two observers for image quality, level of confidence and presence, location, and classification of vascular malformations. The interobserver agreement was calculated using conventional MRA as the standard of reference. RESULTS On the basis of time-resolved MRA, nine of the lesions were categorized as high-flow arteriovenous malformations (AVMs), the remaining 13 lesions were categorized as low-flow vascular malformations or hemangiomas. There was no significant difference in the image quality grading scores between the two observers for time-resolved MRA (p = 0.61) and conventional MRA (p = 0.54). The kappa coefficient revealed good agreement (κ = 0.76) between time-resolved MRA and conventional MRA. Both observers visualized fine vascular details with higher confidence in two patients on conventional MRA. The additional functional information regarding feeding artery and flow patterns provided by time-resolved MRA was confirmed by digital subtraction in all nine cases. CONCLUSION Time-resolved MRA provided the temporal information needed for the appropriate classification of vascular malformations, enabling visualization of both the arterial feeders and draining veins. Furthermore, time-resolved MRA has the potential to be used as an initial and screening diagnostic tool obviating conventional MRA to categorize these lesions and determine their extent to correctly guide treatment.

Low-Dose, Time-Resolved, Contrast-Enhanced 3D MR Angiography in the Assessment of the Abdominal Aorta and Its Major Branches at 3 Tesla

RATIONALE AND OBJECTIVES The aims of this study were to evaluate the effectiveness of low-dose, contrast-enhanced (CE), time-resolved, three-dimensional magnetic resonance angiography (MRA) in the assessment of the abdominal aorta and its major branches at 3 T and to compare the results with those of high-spatial resolution CE MRA. MATERIALS AND METHODS Twenty-two consecutive patients (eight men, 14 women; mean age, 43.9 +/- 17.9 years) underwent CE time-resolved three-dimensional MRA and high-spatial resolution three-dimensional MRA. Studies were performed using a 3-T magnetic resonance system; gadolinium-based contrast medium was administered at a dose of 3 to 5 mL for time-resolved MRA, followed by 0.1 mmol/kg gadopentetate dimeglumine for single-phase CE MRA. For analysis purposes, the abdominal arterial system was divided into 11 arterial segments, and image quality as well as the presence and degree of vascular pathology were evaluated by two independent magnetic resonance radiologists. RESULTS A total of 242 arterial segments were visualized with good image quality. Time-resolved MRA was able to visualize the majority of arterial segments with good definition in the diagnostic range. Vascular pathologies (stenosis, occlusion) or abnormal vascular anatomy was detected in 19 arterial segments, with good interobserver agreement (kappa = 0.78). All image findings were detected with time-resolved CE MRA by both observers and were confirmed by correlative imaging. CONCLUSION Low-dose, time-resolved MRA at 3 T yields rapid and important anatomic and functional information in the evaluation of the abdominal vasculature. Because of its limited spatial resolution, time-resolved MRA is inferior to CE MRA in demonstrating fine vascular details.