Ioannis Seimenis

Magnetic Resonance Angiography, Function and Viability Evaluation in Patients with Kawasaki Disease

OBJECTIVESnWe evaluated the ability of magnetic resonance imaging to perform a noninvasive assessment of coronary arteries, function and viability in one examination in a population with Kawasaki disease.nnnBACKGROUNDnMagnetic resonance angiography (MRA) can identify coronary abnormalities in patients with Kawasaki disease (KD). Contrast enhanced cardiovascular magnetic resonance (CeCMR) is the current gold standard for scar detection. Steady-state, free precession (SSFP) cine is a reliable technique to evaluate myocardial function and wall motion.nnnMETHODSnTwenty patients with KD aged 7-12 yrs, were examined. Coronary MRA was performed using a 1.5 T system with two ECG-triggered pulse sequences. CeCMR images were acquired 15 minutes after the i.v. injection of 0.1 mmol/kg Gd-DTPA using an inversion recovery sequence. SSFP cines were acquired using 6-mm short-axis slices from the atrioventricular ring to the apex.nnnRESULTSnAneurysms of the coronary arteries were identified in 7 patients and coronary ectasia was present in the remaining 12 patients while 1 patient had both. Transmural anterior-apical scar was detected by ceCMR in two cases, while small inferior necrosis was identified in another 2 cases. Left ventricular function was deteriorated only in the two patients with antero-apical infarction. The presence of myocardial infarction was detected in the territory supplied by the involved coronary artery.nnnCONCLUSIONnIn Kawasaki disease MRA, SSFP cine and ceCMR are able to perform noninvasive coronary artery evaluation, function and infarct detection in a single study.

Multiscale Amplitude-Modulation Frequency-Modulation (AM–FM) Texture Analysis of Multiple Sclerosis in Brain MRI Images

This study introduces the use of multiscale amplitude modulation-frequency modulation (AM-FM) texture analysis of multiple sclerosis (MS) using magnetic resonance (MR) images from brain. Clinically, there is interest in identifying potential associations between lesion texture and disease progression, and in relating texture features with relevant clinical indexes, such as the expanded disability status scale (EDSS). This longitudinal study explores the application of 2-D AM-FM analysis of brain white matter MS lesions to quantify and monitor disease load. To this end, MS lesions and normal-appearing white matter (NAWM) from MS patients, as well as normal white matter (NWM) from healthy volunteers, were segmented on transverse T2-weighted images obtained from serial brain MR imaging (MRI) scans (0 and 6-12 months). The instantaneous amplitude (IA), the magnitude of the instantaneous frequency (IF), and the IF angle were extracted from each segmented region at different scales. The findings suggest that AM-FM characteristics succeed in differentiating 1) between NWM and lesions; 2) between NAWM and lesions; and 3) between NWM and NAWM. A support vector machine (SVM) classifier succeeded in differentiating between patients that, two years after the initial MRI scan, acquired an EDSS ≤ 2 from those with EDSS >; 2 (correct classification rate = 86%). The best classification results were obtained from including the combination of the low-scale IA and IF magnitude with the medium-scale IA. The AM-FM features provide complementary information to classical texture analysis features like the gray-scale median, contrast, and coarseness. The findings of this study provide evidence that AM-FM features may have a potential role as surrogate markers of lesion load in MS.

Correlation Between Magnetic Resonance Angiography (MRA) and Quantitative Coronary Angiography (QCA) in Ectatic Coronary Vessels

Coronary artery ectasia (CAE) is defined as a dilatation of an arterial segment to a diameter at least 1.5 times that of the adjacent normal artery. The correct follow-up of ectatic vessels is hampered by the need for repeat angiograms. In this work we compared quantitative coronary angiography (QCA) measurements of the diameter of the proximal most ectatic part of coronary vessels, with corresponding measurements obtained by magnetic resonance angiography (MRA) using both gradient echo and turbo spin echo imaging sequences. Fifteen patients (14 male), aged 45-65 years, with known CAE were prospectively studied. Two electrocardiogram (ECG)-triggered pulse sequences were implemented for coronary magnetic resonance angiography. The first was a three-dimensional (3D), segmented, k-space gradient-echo sequence, employing a T2-weighted preparation prepulse and a frequency-selective, fat-saturation prepulse to enhance white blood (WB) contrast of the coronary arteries. The second sequence was an M2D dual Inversion Recovery (IR) Turbo Spin-Echo with a linear k-space acquisition scheme, providing black-blood (BB) contrast of the coronaries. All scans were carried out with the patient free breathing using a 2D, real-time Navigator beam, for respiratory motion tracking and gating. All patients underwent QCA, and the diameter of the proximal most ectatic part of each vessel was measured and compared with white-blood and black-blood MRA measurements. The average length of continuously visualized LM, LAD, LCx, and RCA by MRA was 2.5 +/- 0.3, 5.8 +/- 0.8, 3.9 +/- 1.0, and 7.2 +/- 1.2 cm, respectively. There were no statistically significant differences between diameter measurements of the proximal most ectatic part of each vessel, obtained with WB and BB sequences. There was a close correlation between MRA and QCA measurements (r = 0.87, p < 0.001). Bland-Altman analysis showed no systematic differences between the examined methods, over the whole range of vessel diameters measured. Coronary MRA is in close correlation with QCA for CAE detection. Magnetic resonance angiography, being noninvasive, may prove of significant value for the efficient follow-up of these patients.

Effect of Posture Change on the Geometric Features of the Healthy Carotid Bifurcation

Segmented cross-sectional MRI images were used to construct 3-D virtual models of the carotid bifurcation in ten healthy volunteers. Geometric features, such as bifurcation angle, internal carotid artery (ICA) angle, planarity angle, asymmetry angle, tortuosity, curvature, bifurcation area ratio, ICA/common carotid artery (CCA), external carotid artery (ECA)/CCA, and ECA/ICA diameter ratios, were calculated for both carotids in two head postures: 1) the supine neutral position; and 2) the prone sleeping position with head rotation to the right (~80°). The results obtained have shown that head rotation causes 1) significant variations in bifurcation angle [32% mean increase for the right carotid (RC) and 21% mean decrease for the left carotid (LC)] and internal carotid artery angle (97% mean increase for the RC, 43% mean decrease for the LC); 2) a slight increase in planarity and asymmetry angles for both RC and LC; 3) minor and variable curvature changes for the CCA and for the branches; 4) slight tortuosity changes for the braches but not for the CCA; and 5) unsubstantial alterations in area and diameter ratios (percentage changes <;10%). The significant geometric changes observed in most subjects with head posture may also cause significant changes in bifurcation hemodynamics and warrant future investigation of the hemodynamic parameters related to the development of atherosclerotic disease such as low oscillating wall shear stress and particle residence times.

Coronary flow evaluation by TIMI frame count and magnetic resonance flow velocity in patients with coronary artery ectasia

PURPOSEnCoronary artery ectasia (CAE) is defined as a dilatation of an arterial segment to a diameter at least 1.5 times that of the adjacent artery. It is characterized by slow flow, predisposing to thrombosis. The TIMI frame count (TFC) technique has been successfully used for the assessment of coronary flow velocity using coronary angiograms (CA). Our aim was to compare TFC with magnetic resonance peak flow velocity (PFV) for the evaluation of the coronary flow in patients with CAE.nnnMETHODSnFifteen male patients with CAE, aged 45-60 yrs, and 15 age-matched male controls were studied by both techniques. Only patients without coronary obstructive disease were included. Magnetic resonance coronary angiography (MRA) was performed with a 1.5T scanner. The most ectatic part of the proximal 1/3 of the vessel involved was examined. Velocity-encoded MR images were acquired in a double oblique imaging plane, which was perpendicular to the same ectatic segment. The findings were compared with TFC results.nnnRESULTSnTen patients had RCA ectasia and five LAD ectasia. In CAE patients, peak flow velocity was 10.7 +/- 1.4 cm/sec in RCA and 11.4 +/- 2.3 cm/sec in LAD. TFC was 42.9 +/- 7.4 in RCA and 52.0 +/- 20.1 in LAD. In controls, peak flow velocity was 18.1 +/- 1.9 in RCA and 21.0 +/- 1.7 cm/sec in LAD. TFC was 20.4 +/- 1.59 in RCA and 19.8 +/- 1.12 in LAD. Controls had significantly higher peak flow velocity (p < 0.001) and lower TFC (p < 0.001) in both RCA and LAD, compared to patients with CAE. In patients with CAE, there was a negative correlation between PFV and TFC measurements (r = -0.74, p < 0.001).nnnCONCLUSIONnCoronary flow in CAE patients can be assessed both by TFC and PFV. The noninvasive nature of PFV gives the opportunity for serial, easily repeatable, flow evaluation in these patients.

Quantitative analysis of brain white matter lesions in multiple sclerosis subjects

In this study the value of magnetic resonance image (MRI) shape and texture analysis was assessed in multiple sclerosis (MS) subjects, both in differentiating between normal or normal appearing and abnormal tissue and in assessing disease onset. Shape and texture analysis was carried out in normal brain white matter and lesions detected in transverse sections of T2-weighted magnetic resonance (MR) images acquired from 22 symptomatic untreated subjects. All detected brain lesions were manually segmented by an experienced MS neurologist and confirmed by a radiologist. The results showed that there was no significant difference for most of the shape features and for all of the texture features between MS lesions at 0 and 6–12 months. For some texture features there was significant difference between normal or normal appearing tissue and MS lesions at 0 and 6–12 months. Further research with more subjects is required for computing shape and texture features that may provide information for better and earlier differentiation between normal tissue and MS lesions.

Relationship of Number of Phases per Cardiac Cycle and Accuracy of Measurement of Left Ventricular Volumes, Ejection Fraction, and Mass

In cine cardiac magnetic resonance imaging (MRI) studies, for any preset imaging parameters the number of phases per cardiac cycle for a single slice is proportional to breath-hold duration. We investigated the relationship between the accuracy of measurement of left ventricular (LV) end-diastolic and end-systolic volumes (EDV and ESV, respectively), mass and ejection fraction (EF), and the number of phases acquired per cardiac cycle. Twelve adult volunteers underwent cardiac MRI and five complete LV functional studies were obtained with 8, 11, 14, 17, and 20 phases per cardiac cycle. We calculated LV volumes, EF, and mass for each acquisition, and compared them using the 20-phase acquisition as the reference standard. The scan duration was proportional to the number of phases acquired. There was a systematic underestimation of LV, EDV, and EF, with decreasing number of phases. Differences from the reference standard became significant for the 8-phase acquisition (p<0.05). Subgroup analysis showed that only those with slower heart rates (<65/min) had significant differences in EDV, but not in EF, for the 8-phase acquisition. For those with faster heart rates, no differences were detected between the different acquisitions. There were no significant differences between all acquisitions for the LV ESV and mass. We conclude that at least 11 phases per cardiac cycle are needed to maintain accuracy for cine cardiac MRI studies. Decreasing the number of phases per cardiac cycle beyond this cutoff may introduce significant error of measurement, particularly for the left ventricular EDV and EF and especially for those with bradycardia, and should be avoided.

An Approach for Preoperative Planning and Performance of MR-guided Interventions Demonstrated With a Manual Manipulator in a 1.5T MRI Scanner

PurposeThe aim of this work was to develop and test a general methodology for the planning and performance of robot-assisted, MR-guided interventions. This methodology also includes the employment of software tools with appropriately tailored routines to effectively exploit the capabilities of MRI and address the relevant spatial limitations.MethodsThe described methodology consists of: (1) patient-customized feasibility study that focuses on the geometric limitations imposed by the gantry, the robotic hardware, and interventional tools, as well as the patient; (2) stereotactic preoperative planning for initial positioning of the manipulator and alignment of its end-effector with a selected target; and (3) real-time, intraoperative tool tracking and monitoring of the actual intervention execution. Testing was performed inside a standard 1.5T MRI scanner in which the MR-compatible manipulator is deployed to provide the required access.ResultsA volunteer imaging study demonstrates the application of the feasibility stage. A phantom study on needle targeting is also presented, demonstrating the applicability and effectiveness of the proposed preoperative and intraoperative stages of the methodology. For this purpose, a manually actuated, MR-compatible robotic manipulation system was used to accurately acquire a prescribed target through alternative approaching paths.ConclusionsThe methodology presented and experimentally examined allows the effective performance of MR-guided interventions. It is suitable for, but not restricted to, needle-targeting applications assisted by a robotic manipulation system, which can be deployed inside a cylindrical scanner to provide the required access to the patient facilitating real-time guidance and monitoring.

Carbon beam dosimetry using VIP polymer gel and MRI

VIP polymer gel dosimeter was used for Carbon ion beam dosimetry using a 150 MeV/n beam with 10 Gy plateau dose and a SOBP irradiation scheme with 5 Gy Bragg peak dose. The results show a decrease by 8 mm in the expected from Monte Carlo simulation range in water, suggesting that the dosimeter is non water equivalent. However VIP shows efficiency close to 1 in the plateau region and significantly reduced efficiency in the peak. On the other hand the SOBP results yield an efficiency close to 1 in the SOBP implying that the dose response of the VIP dosimeter may not be solely related to LET.

On the use of VIP gel dosimetry in HDR brachytherapy

An experimental procedure is discussed with regard to its potential in 192Ir HDR brachytherapy dosimetry. Two samples of VIP normoxic gel formulation are used; one for gel response calibration and the other for acquiring experimental data. Using the same irradiation method for both calibration and experimental purposes (an 192Ir HDR brachytherapy source) and treating the two samples identically (i.e. the two samples are prepared, irradiated and scanned at the same time and stored together at all times) leads to total dose uncertainties comparable to those of other well established dosimetry methods over a significant dose range (~7Gy-40Gy). In this dose range, the described procedure can be used to either acquire absolute dosimetry results for the characterisation of new 192Ir HDR brachytherapy sources, or to facilitate the planning of relative dosimetry experiments for the verification of calculations by new generation treatment planning systems that are currently phasing in, in complex 3D dose distributions involving inhomogeneities and finite medium geometries.