Keigo Kawaji

Role of Perfusion at Rest in the Diagnosis of Myocardial Infarction Using Vasodilator Stress Cardiovascular Magnetic Resonance

In clinical practice, perfusion at rest in vasodilator stress single-photon emission computed tomography is commonly used to confirm myocardial infarction (MI) and ischemia and to rule out artifacts. It is unclear whether perfusion at rest carries similar information in cardiovascular magnetic resonance (CMR). We sought to determine whether chronic MI is associated with abnormal perfusion at rest on CMR. We compared areas of infarct and remote myocardium in 31 patients who underwent vasodilator stress CMR (1.5 T), had MI confirmed by late gadolinium enhancement (LGE scar), and coronary angiography within 6 months. Stress perfusion imaging during gadolinium first pass was followed by reversal with aminophylline (75 to 125 mg), rest perfusion, and LGE imaging. Resting and peak-stress time-intensity curves were used to obtain maximal upslopes (normalized by blood pool upslopes), which were compared between infarcted and remote myocardial regions of interest. At rest, there was no significant difference between the slopes in the regions of interest supplied by arteries with and without stenosis >70% (0.31 ± 0.16 vs 0.26 ± 0.15 1/s), irrespective of LGE scar. However, at peak stress, we found significant differences (0.20 ± 0.11 vs 0.30 ± 0.22 1/s; p <0.05), reflecting the expected stress-induced ischemia. Similarly, at rest, there was no difference between infarcted and remote myocardium (0.27 ± 0.14 vs 0.30 ± 0.17 1/s), irrespective of stenosis, but significant differences were seen during stress (0.21 ± 0.16 vs 0.28 ± 0.18 1/s; p <0.001), reflecting inducible ischemia. In conclusion, abnormalities in myocardial perfusion at rest associated with chronic MI are not reliably detectable on CMR images. Accordingly, unlike single-photon emission computed tomography, normal CMR perfusion at rest should not be used to rule out chronic MI.

REGIONAL RIGHT VENTRICULAR EJECTION FRACTION AND CARDIAC OUTPUT IN REPAIRED TETRALOGY OF FALLOT

Patients with repaired Tetralogy of Fallot (rTOF) have changes in global and regional right ventricular (RV) function due to residual pulmonic valve stenosis and insufficiency, anatomic defects, surgical scar or conduction delays. Global RV volumes and ejection fraction (EF) obtained from

Three-dimensional changes in regional right ventricular curvature and function in tetralogy of fallot

Background Many patients with Tetralogy of Fallot (TOF) have residual pulmonic stenosis and/or regurgitation after surgical repair, leading to maladaptive right ventricular (RV) remodeling. Cardiovascular magnetic resonance (CMR) is currently the gold standard for evaluating RV size and function. Analysis of regional volume and three-dimensional (3D) curvature of the RV from CMR images may provide new insights into the remodeling process. The aim of this study is to describe RV remodeling by characterizing regional endocardial surface curvature and function in patients with TOF. Methods CMR (1.5T Philips Achieva) was performed in subjects with repaired TOF (N=17, age range 9-53 years) and healthy volunteers (N=10, age range 23-43 years). The RV end-diastolic and end-systolic endocardial surfaces were manually segmented from a contiguous stack of short axis cine slices to construct a 3D model using custom software (figure). This model was used to measure regional volume and ejection fraction for the RV inflow, outflow, and trabecular regions. Local endocardial surface curvature was displayed on a color map of the 3D volume surface and regional curvature was calculated for the RV inflow, outflow, trabecular, free wall, and septal segments. The values for curvature were indexed to volume to remove the influence of volume between regions. The parameters from individuals with TOF were compared to those acquired from the healthy volunteers. Results As shown in the table, individuals with TOF had larger global RV volume and reduced ejection fraction when compared to controls. The trabecular region had relatively preserved ejection fraction, despite exhibiting the most enlargement. Conversely, the outflow and inflow regions had greater reductions in ejection fraction but only mild enlargement. The Trabecular region enlargement coincided with increased regional curvature, which was not as striking in the inflow and outflow regions. Those with TOF had higher overall free wall curvature. Septal curvature in TOF patients was higher (slightly convex) compared to controls (slightly concave). Global curvature, combining all septal and free wall regions, was higher in TOF patients. Conclusions Using analysis of RV 3D regional curvature and volumes from CMR images, we show that individuals with repaired TOF have regional variation in RV remodeling and function. Further evaluation is required to understand the clinical implications of this variable remodeling.

Multicenter reproducibility of quantitative susceptibility mapping in a gadolinium phantom using MEDI+0 automatic zero referencing: Magnetic Resonance in Medicine

To determine the reproducibility of quantitative susceptibility mapping at multiple sites on clinical and preclinical scanners (1.5 T, 3 T, 7 T, and 9.4 T) from different vendors (Siemens, GE, Philips, and Bruker) for standardization of multicenter studies.

Three-dimensional analysis of regional right ventricular shape and function in repaired tetralogy of Fallot using cardiovascular magnetic resonance

BACKGROUND Patients with surgically repaired tetralogy of Fallot (rTOF) often have residual pulmonic valve regurgitation, leading to abnormal remodeling and dysfunction of the right ventricle often requiring pulmonic valve replacement. We tested the hypothesis that 3D analysis of right ventricular (RV) shape and function may reveal differences in regional adaptive remodeling that occurs in patients with rTOF, depending on whether a transannular patch (TAP) was utilized. METHODS Forty patients with rTOF who underwent cardiac magnetic resonance imaging (1.5 T), including 20 with and 20 without TAP, and 10 normal controls were studied. Images were analyzed to measure RV endocardial curvature and global and regional volume and function. RESULTS RV ejection fraction (EF) was 42 ± 11% in TAP and 38 ± 9% in no-TAP (p = 0.19), both lower than 54 ± 3% in controls (p < 0.01). Left ventricular (LV) EF was 54 ± 9% in TAP, 54 ± 8% in no-TAP (p = 0.87) and 61 ± 16% in controls (both p < 0.01). Indexed LV end-diastolic volumes were higher in no-TAP than in TAP subgroup (p = 0.02). With TAP, mid RV septum showed lower curvature during diastole (less convex), than the mid and apical free walls and free wall adjacent to the RV outflow tract (RVOT; more convex). There were no differences in curvature during systole between rTOF subgroups but mid and RVOT free walls showed higher curvature versus controls. CONCLUSIONS This is the first study to comprehensively describe the influence of TAP on changes in regional RV shape in patients with rTOF. Understanding these differences may help guide therapeutic options for residual pulmonary valve regurgitation in rTOF patients.

A fast, noniterative approach for accelerated high‐temporal resolution cine‐CMR using dynamically interleaved streak removal in the power‐spectral encoded domain with low‐pass filtering (DISPEL) and modulo‐prime spokes (MoPS)

Purpose To introduce a pair of accelerated non‐Cartesian acquisition principles that when combined, exploit the periodicity of k‐space acquisition, and thereby enable acquisition of high‐temporal cine Cardiac Magnetic Resonance (CMR). Methods The mathematical formulation of a noniterative, undersampled non‐Cartesian cine acquisition and reconstruction is presented. First, a low‐pass filtering step that exploits streaking artifact redundancy is provided (i.e., Dynamically Interleaved Streak removal in the Power‐spectrum Encoded domain with Low‐pass filtering [DISPEL]). Next, an effective radial acquisition for the DISPEL approach that exploits the property of prime numbers is described (i.e., Modulo‐Prime Spoke [MoPS]). Both DISPEL and MoPS are examined using numerical simulation of a digital heart phantom to show that high‐temporal cine‐CMR is feasible without removing physiologic motion vs aperiodic interleaving using Golden Angles. The combined high‐temporal cine approach is next examined in 11 healthy subjects for a time–volume curve assessment of left ventricular systolic and diastolic performance vs conventional Cartesian cine‐CMR reference. Results The DISPEL method was first shown using simulation under different streak cycles to allow separation of undersampled radial streaking artifacts from physiologic motion with a sufficiently frequent streak‐cycle interval. Radial interleaving with MoPS is next shown to allow interleaves with pseudo‐Golden‐Angle variants, and be more compatible with DISPEL against irrational and nonperiodic rotation angles, including the Golden‐Angle‐derived rotations. In the in vivo data, the proposed method showed no statistical difference in the systolic performance, while diastolic parameters sensitive to the cines temporal resolution were statistically significant (P < 0.05 vs Cartesian cine). Conclusions We demonstrate a high‐temporal resolution cine‐CMR using DISPEL and MoPS, whose streaking artifact was separated from physiologic motion.

A novel profile/view ordering with a non‐convex star shutter for high‐resolution 3D volumetric T1 mapping under multiple breath‐holds

To examine a novel non‐convex star ordering/shutter for reducing the number of breath‐holds in cardiac three‐dimensional (3D) T1 Mapping MRI with multiple breath‐holds.

3D late gadolinium enhanced cardiovascular MR with CENTRA-PLUS profile/view ordering: Feasibility of right ventricular myocardial damage assessment using a swine animal model

AIMS To develop a high-resolution, 3D late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (MRI) technique for improved assessment of myocardial scars, and evaluate its performance against 2D breath-held (BH) LGE MRI using a surgically implanted animal scar model in the right ventricle (RV). METHODS AND RESULTS A k-space segmented 3D LGE acquisition using CENTRA-PLUS (Contrast ENhanced Timing Robust Acquisition with Preparation of LongitUdinal Signal; or CP) ordering is proposed. 8 pigs were surgically prepared with cardiac patch implantation in the RV, followed in 60days by 1.5T MRI. LGE with Phase-Sensitive Inversion Recovery (PSIR) were performed as follows: 1) 2DBH using pneumatic control, and 2) navigator-gated, 3D free-breathing (3DFB)-CP-LGE with slice-tracking. The animal heart was excised immediately after cardiac MR for scar volume quantification. RV scar volumes were also delineated from the 2DBH and 3DFB-CP-LGE images for comparison against the surgical standard. Apparent scar/normal tissue signal-to-noise ratio (aSNR) and contrast-to-noise ratio (aCNR) were also calculated. 3DFB-CP-LGE technique was successfully performed in all animals. No difference in aCNR was noted, but aSNR was significantly higher using the 3D technique (p<0.05). Against the surgical reference volume, the 3DFB-CP-LGE-derived delineation yielded significantly less volume quantification error compared to 2DBH-derived volumes (15±10% vs 55±33%; p<0.05). CONCLUSION Compared to conventional 2DBH-LGE, 3DFB-LGE acquisition using CENTRA-PLUS provided superior scar volume quantification and improved aSNR.

IMPLEMENTATION OF A WIDEBAND LATE GADOLINIUM ENHANCEMENT CARDIAC MAGNETIC RESONANCE PROTOCOL TO IMPROVE ASSESSMENT OF MYOCARDIAL SCAR IN PATIENTS WITH IMPLANTABLE CARDIOVERTER DEFIBRILLATORS

Background: Severe susceptibility artifacts (SA) limit the use of cardiac magnetic resonance (CMR) in patients with implantable cardioverter defibrillators (ICDs). The use of a previously developed wideband (WB) late gadolinium enhancement (LGE) technique may ameliorate these artifacts. We sought to

The extracellular matrix patch implanted in the right ventricle evaluated with cardiovascular magnetic resonance protocol to assess regional physio-mechanical properties

OBJECTIVES An extracellular matrix patch was implanted in the porcine right ventricle for in situ myocardial regeneration. A newly developed cardiovascular magnetic resonance protocol was utilized to investigate the regional physio-mechanical function of the patch. METHODS Cardiovascular magnetic resonance was performed at 60-day after the porcine right ventricular wall full thickness substitution with an extracellular matrix cardiac patch (n = 5). Dacron patches and remote normal right ventricle served as control (n = 5/each). Late gadolinium enhancement, strain encoding and rest perfusion were measured for scar/patch detection, regional contractility and tissue perfusion. Image analyses were performed by two observers to validate interobserver reproducibility. RESULTS All imaging sequences were successfully obtained. The patches were located with late gadolinium enhancement imaging in 95% accuracy. All the parameters demonstrated significant differences among extracellular matrix, Dacron and normal myocardium (P < 0.05), which correlated with histological findings, including constructive remodelling with nascent myocardium and profound vasculogenesis/angiogenesis in extracellular matrix patches, and scar formation in Dacron. Bland-Altman analysis demonstrated good interobserver reproducibility with minimal bias (strain encoding/peak strain: mean difference = -0.32%, 95% limits of agreement = -1.2 to 0.57, correlation = 0.97; rest perfusion/relative maximum upslope: mean difference = -0.74, 95% limits of agreement = -2.0 to 0.53, correlation = 0.92), along with excellent correlation obtained from linear regression (strain encoding: R2 = 0.93; rest perfusion: R2 = 0.85). CONCLUSIONS With the cardiovascular magnetic resonance protocol, we successfully confirmed early signs of functional myocardial regeneration in implanted extracellular matrix patches. This approach is promising in assessing in situ regional physio-mechanical properties and degree of regeneration of implanted tissue-engineered materials.