Magnetic resonance imaging dynamic contrast enhancement (DCE) characteristics of healed myocardial infarction differ from viable myocardium

Purpose

To determine whether healed myocardial infarction alters dynamic contrast-enhancement (DCE) curve shapes as well as late gadolinium-enhancement (LGE).

Materials and methods

Twenty patients with chronic myocardial infarction underwent MR imaging at 1.5 T with blood and myocardial T1 measurements before and after contrast administration for forty minutes. Viable and infarcted myocardial partition coefficients were calculated using multipoint slope methods for ten different DCE sampling intervals and windows. Partition coefficients and coefficients of determination were compared with paired statistical tests to assess the linearity of DCE curve shapes over the 40 min time period.

Results

Calculated partition coefficients did not vary significantly between methods (p = 0.325) for viable myocardium but did differ for infarcted myocardium (p < 0.001), indicating a difference in infarcted DCE. There was a significant difference between viable and infarcted myocardial partition coefficients estimates for all methods with the exception of methods that included measurements during the first 10 min after contrast agent administration.

Conclusion

Myocardial partition coefficients calculated from a slope calculation vary in healed myocardial infarction based on the selection of samples due to non-linear DCE curve shapes. Partition coefficient calculations are insensitive to data sampling effects in viable myocardium due to linear DCE curve shapes.     

H Magnetic resonance imaging of rigid polymeric solids

Implementation of the ¹H magnetic resonance single-point imaging technique has provided new opportunities for the direct imaging of rigid solids, particularly semicrystalline polymers with spin-spin relaxation times, T^*₂, of the order of 10 μs and greater. Potential applications of industrial relevance in the following areas are briefly discussed and illustrated: fabricated/processed parts, photochemical degradation, oxidation, and blend characterization.     

Optimizing tissue contrast in magnetic resonance imaging

Magnetic resonance imaging demands that tissue contrast and signal-to-noise advantages be sought in each component of the imaging system. One component of magnetic resonance imaging in which contrast and signal-to-noise ratios are easily manipulated is in the choice of pulse sequences and interpulse delay times. This article provides a general method for determining the best choices of interpulse delay times in pulse sequences and applies that method to saturation recovery, inversion recovery, and spin-echo sequences. Saturation recovery and inversion recovery sequences with rephasing pulses, and tissues with unequal hydrogen densities are considered. Optimization of pulse sequences is carried out for the two distinct cases of (a) a fixed number of sequence repetitions and (b) a fixed total imaging time. Analytic expressions are derived or approximate expressions are provided for the interpulse delay times that optimize contrast-to-noise ratios in each pulse sequence. The acceptable range of interpulse delay times to obtain reasonable contrast using each pulse sequence is discussed.     

H Magnetic resonance imaging and P magnetic resonance spectroscopy in experimental filariasis

¹H Magnetic resonance imaging and ³¹P magnetic resonance spectroscopy (MRS) have been carried out in experimental rodent filariasis, i.e., Acanthocheilonema viteae infection in the rodent host, Mastomys coucha. The T₂-weighted image of the infected host shows fine hyperintense thread like structures of adult filariid nests in the cervical region. ³¹P MRS of normal and infected hosts, localized over the same region of interest, show seven major peaks corresponding to phosphomonoesters (including glucose-6-phosphate, fructose-6-phosphate, fructose-1-6-diphosphate, phosphorylcholine, and adenine monophosphate or AMP), inorganic phosphate, glycerophosphorylcholine, phosphoenolpyruvate, phosphocreatine and nucleoside di- and tri-phosphates. Concentrations of phosphomonoesters (PMEs) are higher in the normal rodent compared with the infected ones. In vivo ³¹P MRS provides a non-invasive assessment of tissue bioenergetics and phospholipid metabolism.     

Time resolved spectroscopic NMR imaging using hyperpolarized Xe

We have visualized the melting and dissolution processes of xenon (Xe) ice into different solvents using the methods of nuclear magnetic resonance (NMR) spectroscopy, imaging, and time resolved spectroscopic imaging by means of hyperpolarized ¹²⁹Xe. Starting from the initial condition of a hyperpolarized solid Xe layer frozen on top of an ethanol (ethanol/water) ice block we measured the Xe phase transitions as a function of time and temperature. In the pure ethanol sample, pieces of Xe ice first fall through the viscous ethanol to the bottom of the sample tube and then form a thin layer of liquid Xe/ethanol. The xenon atoms are trapped in this liquid layer up to room temperature and keep their magnetization over a time period of 11 min. In the ethanol/water mixture (80 vol%/20%), most of the polarized Xe liquid first stays on top of the ethanol/water ice block and then starts to penetrate into the pores and cracks of the ethanol/water ice block. In the final stage, nearly all the Xe polarization is in the gas phase above the liquid and trapped inside the pores. NMR spectra of homogeneous samples of pure ethanol containing thermally polarized Xe and the spectroscopic images of the melting process show that very high concentrations of hyperpolarized Xe (about half of the density of liquid Xe) can be stored or delivered in pure ethanol.     

Magnetic resonance imaging of an infected urethral diverticulum: A case report

We present a case report of a urethral diverticulum where magnetic resonance imaging suggested infected contents of the urethral diverticulum besides providing superb detail of periurethral anatomy. The critical clinical question was answered.     

Magnetic resonance microscopy of iron transport in methanogenic granules

Interactions between anaerobic biofilms and heavy metals such as iron, cobalt or nickel are largely unknown. Magnetic resonance imaging (MRI) is a non-invasive method that allows in situ studies of metal transport within biofilm matrixes. The present study investigates quantitatively the penetration of iron (1.75 mM) bound to ethylenediaminetetraacetate (EDTA) into the methanogenic granules (spherical biofilm). A spatial resolution of 109 × 109 × 218 μm³ and a temporal resolution of 11 min are achieved with 3D Turbo Spin Echo (TSE) measurements. The longitudinal relaxivity, i.e. the slope the dependence of the relaxation rate (1/T₁) on the concentration of paramagnetic metal ions, was used to measure temporal changes in iron concentration in the methanogenic granules. It took up to 300 min for the iron–EDTA complex ([FeEDTA]²⁻) to penetrate into the methanogenic granules (3–4 mm in diameter). The diffusion was equally fast in all directions with irregularities such as diffusion-facilitating channels and diffusion-resistant zones. Despite these irregularities, the overall process could be modeled using Fick’s equations for diffusion in a sphere, because immobilization of [FeEDTA]²⁻ in the granular matrix (or the presence of a reactive barrier) was not observed. The effective diffusion coefficient (D_ejf) of [FeEDTA]²⁻ was found to be 2.8 × 10⁻¹¹ m² s⁻¹, i.e. approximately 4% of D_ejf of [FeEDTA]²⁻ in water. The Fickian model did not correspond to the processes taking place in the core of the granule (3–5% of the total volume of the granule), where up to 25% over-saturation by iron (compare to the concentration in the bulk solution) occurred.     

High-field magnetic resonance imaging using solenoid radiofrequency coils

High-resolution magnetic resonance imaging using dedicated high-field radiofrequency micro-coils at 16.4 T (700 MHz) was investigated. Specific solenoid coils primarily using silver and copper as conductors with enamel and polyurethane coatings were built to establish which coil configuration produces the best image. Image quality was quantified using signal-to-noise ratio and signal variation over regions of interest. Benchmarking was conducted using 5-mm diameter coils, as this size is comparable to an established coil of the same size. Our 1.4-mm-diameter coils were compared directly to each other, from which we deduce performance as a function of conductor material and coating. A variety of materials and conductor coatings allowed us to choose an optimal design, which we used to image a kidney section at 10-micron resolution. We applied zero-fill extrapolation to achieve 5-micron resolution.     

Novel methodology for 3D reconstruction of carotid arteries and plaque characterization based upon magnetic resonance imaging carotid angiography data

In this study, we present a novel methodology that allows reliable segmentation of the magnetic resonance images (MRIs) for accurate fully automated three-dimensional (3D) reconstruction of the carotid arteries and semiautomated characterization of plaque type. Our approach uses active contours to detect the luminal borders in the time-of-flight images and the outer vessel wall borders in the T(1)-weighted images. The methodology incorporates the connecting components theory for the automated identification of the bifurcation region and a knowledge-based algorithm for the accurate characterization of the plaque components. The proposed segmentation method was validated in randomly selected MRI frames analyzed offline by two expert observers. The interobserver variability of the method for the lumen and outer vessel wall was -1.60%±6.70% and 0.56%±6.28%, respectively, while the Williams Index for all metrics was close to unity. The methodology implemented to identify the composition of the plaque was also validated in 591 images acquired from 24 patients. The obtained Cohen's k was 0.68 (0.60-0.76) for lipid plaques, while the time needed to process an MRI sequence for 3D reconstruction was only 30 s. The obtained results indicate that the proposed methodology allows reliable and automated detection of the luminal and vessel wall borders and fast and accurate characterization of plaque type in carotid MRI sequences. These features render the currently presented methodology a useful tool in the clinical and research arena.     

Short T2 contrast with three-dimensional ultrashort echo time imaging

There is increasing interest in imaging short T2 species which show little or no signal with conventional magnetic resonance (MR) pulse sequences. In this paper, we describe the use of three-dimensional ultrashort echo time (3D UTE) sequences with TEs down to 8 μs for imaging of these species. Image contrast was generated with acquisitions using dual echo 3D UTE with echo subtraction, dual echo 3D UTE with rescaled subtraction, long T2 saturation 3D UTE, long T2 saturation dual echo 3D UTE with echo subtraction, single adiabatic inversion recovery 3D UTE, single adiabatic inversion recovery dual echo 3D UTE with echo subtraction and dual adiabatic inversion recovery 3D UTE. The feasibility of using these approaches was demonstrated in in vitro and in vivo imaging of calcified cartilage, aponeuroses, menisci, tendons, ligaments and cortical bone with a 3-T clinical MR scanner. Signal-to-noise ratios and contrast-to-noise ratios were used to compare the techniques.     

Magnetic resonance velocity imaging of liquid and gas two-phase flow in packed beds

Single-phase liquid flow in porous media such as bead packs and model fixed bed reactors has been well studied by MRI. To some extent this early work represents the necessary preliminary research to address the more challenging problem of two-phase flow of gas and liquid within these systems. In this paper, we present images of both the gas and liquid velocities during stable liquid–gas flow of water and SF₆ within a packing of 5 mm spheres contained within columns of diameter 40 and 27 mm; images being acquired using ¹H and ¹⁹F observation for the water and SF₆, respectively. Liquid and gas flow rates calculated from the velocity images are in agreement with macroscopic flow rate measurements to within 7% and 5%, respectively. In addition to the information obtained directly from these images, the ability to measure liquid and gas flow fields within the same sample environment will enable us to explore the validity of assumptions used in numerical modelling of two-phase flows.     

Assessment of mitral regurgitation by magnetic resonance imaging

To evaluate the potential of magnetic resonance imaging (MRI) in detection and quantification of mitral regurgitation, 26 pts. with echocardiographically or angiographically documented mitral regurgitation were examined using a 0.5 Tesla superconducting magnet. In each patient a multislice-multiphase study in a sagittal-coronal double angulated projection (four-chamber view equivalent) was performed to assess left and right ventricular volumes, ejection fraction and regurgitant fraction. Additionally a blood flow sensitive cine-study (fast field echo: FFE) was done to visualize direction and area of regurgitant jet. MRI data were compared with quantitative and qualitative assessment of mitral regurgitation by angiography, 2D echocardiography, Doppler sonography and color flow mapping. Using the FFE mode MRI was able to detect the regurgitant jet as a typical signal loss within the left atrium in all patients. The ratio of regurgitant jet area/left atrium area as determined by MRI showed a correlation with a comparable ratio from color Doppler sonography of R = 0.87 (p < 0.001). There was also good agreement in semiquantitative grading of mitral regurgitation between MRI and angiography (R = 0.77, p < 0.001). The determination of left and right ventricular stroke volume allowed the calculation of the regurgitant fraction, which showed a correlation with invasively determined regurgitation fraction of R = 0.84 (p < 0.001). These data provide additional information that MRI may be useful as a noninvasive technique to detect and quantify mitral regurgitation.     

Research and progress in magnetic resonance imaging of triple-negative breast cancer

Triple-negative breast cancer (TNBC), which characterized by distinct biological and clinical pathological features, has a worse prognosis because the lack of effective therapeutic targets. Breast MR is the most accurate imaging modality for diagnosis of breast cancer currently. MR imaging recognition could assist in diagnosis, pretreatment planning and prognosis evaluation of TNBC. MR findings of a larger solitary lesion, mass with smooth mass margin, high signal intensity on T₂-weighted images and rim enhancement are typical MRI features associated with TNBC. Further work is necessary about the clinical application of dynamic contrast-enhanced MR imaging (DCE-MRI), DWI and MRS.     

Labeling of macrophages using bacterial magnetosomes and their characterization by magnetic resonance imaging

This work investigated macrophages labeled with magnetosomes for the possible detection of inflammations by MR molecular imaging. Pure magnetosomes and macrophages containing magnetosomes were analyzed using a clinical 1.5 T MR-scanner. Relaxivities of magnetosomes and relaxation rates of cells containing magnetosomes were determined. Peritonitis was induced in two mice. T₁, T₂ and T₂* weighted images were acquired following injection of the probes. Pure magnetosomes and labeled cells showed slight effects on T₁, but strong effects on T₂ and T₂* images. Labeled macrophages were located with magnetic resonance imaging (MRI) in the colon area, thus demonstrating the feasibility of the proposed approach.     

Magnetic resonance measurement of blood flow in peripheral vessels after acute exercise

Velocity-encoded Cine magnetic resonance imaging (MRI) was used to measure blood flow in the anterior tibial artery (AT), posterior tibial artery (PT), and popliteal artery of adult human subjects (mean age 29 yr) before and after 90 s of ankle dorsiflexion exercise. Before exercise, mean flow, peak systolic velocity, and end-diastolic velocity in AT were 8.1 ± 1.6 (SE, n = 6) ml/min, 26.9 ± 2.6 cm/s, and −0.6 ± 0.4 cm/s, respectively. After exercise, mean flow and peak systolic velocity in AT increased by 19-fold and 3-fold, respectively, and end-diastolic velocity increased to 8.7 ± 1.1 cm/s. Flow in popliteal artery above its bifurcation was similar to the sum of flows in AT and PT, both before and after exercise. Flow in AT declined exponentially after exercise with a mean half-time of 4 min. The results demonstrate the utility of MR phase-encoded flow-velocity measurements for physiological studies of peripheral vascular dynamics after exercise.     

Magnetic resonance imaging of coronary arteries and heart valves in a living mouse: techniques and preliminary results

New investigations in MRI of a mouse heart showed high-contrast cardiac images and thereby the possibility of doing functional cardiac studies of in vivo mice. But is MRI, in addition, capable of visualizing microstructures such as the coronary arteries and the heart valves of a living mouse? To answer this question, 2D and 3D gradient echo sequences with and without flow compensation were used to image the coronary arteries. To increase signal-to-noise ratio, a birdcage resonator was optimized for mouse heart imaging. Contrast between blood and myocardium was achieved through the inflow effect. A segmented three-dimensional FLASH sequence acquired with a multiple overlap thin slab technique showed the best results. With this technique an isotropic resolution of 100 microm was achieved. The left coronary artery could be visualized up to the apex of the heart. This is demonstrated with short axis views and 3D surface reconstructions of the mouse heart. The four cardiac valves were also visible with the 3D method.     

Evaluation of left ventricular function with cardiac magnetic resonance imaging using Fourier fitting

The aims of this study were to investigate the applicability of Fourier fitting in the magnetic resonance (MR) evaluation of left ventricular (LV) function and to determine the optimal number of harmonics for fitting. Cine cardiac MR imaging was performed in 10 subjects, and an LV time–volume curve was generated. Fourier fitting was applied to the original curve using 1–10 harmonics, and the qualities of the time–volume curve and first-derivative curve were evaluated. LV functional parameters were calculated from curves generated with and without fitting. The quality of the original time–volume curve was good, and Fourier fitting had no substantial effect on functional parameters obtained directly from the time–volume curve such as ejection fraction. The first-derivative curve generated without fitting showed substantial artificial fluctuation. The application of Fourier fitting depressed the fluctuation and tended to decrease estimates of peak ejection rate and peak filling rate. Five or six harmonics appeared to be appropriate for obtaining a high-quality first-derivative curve. In conclusion, Fourier fitting was indicated to aid in reducing the artificial fluctuation of the first-derivative curve generated from cine cardiac MR imaging and to contribute to the evaluation of functional parameters derived from the first-derivative curve.     

Magnetic resonance imaging with superparamagnetic iron oxide particles for the detection of myocardial reperfusion

The effect of superparamagnetic iron oxide particles on magnetic resonance myocardial signal intensity was examined in order to define the ability of this agent to identify normal, ischemic, and reperfused myocardium. Data were obtained from 6 normal rats (group 1) and from 6 heterotopic isogenic rat heart transplants (group 2) at 4.7 T with a multislice spin-echo sequence. Images were acquired in (a) normal rats before and after the infusion of 36 μmol Fe/kg of AMI-25 (group 1) and (b) rat heart transplants during control, global myocardial ischemia (before and after the injection of 72 μmol Fe/kg of AMI-25), and following reperfusion (group 2). Myocardial signal intensity decreased by 36 ± 4%, p < 0.001, following contrast infusion in normal hearts (group 1). The intensity remained constant in the rat heart transplants (group 2) during coronary occlusion, both before and after the infusion of AMI-25 and decreased by 61 ± 7%, p < 0.001, upon reperfusion. The larger effect of AMI-25 in reperfused as compared to normal myocardium suggests the presence of ischemia-induced hyperemia. There was no significant difference (analysis of variance) among intensities from different myocardial regions in either group at any stage of the experiment. We conclude that the use of AMI-25 permits identification of normal, ischemic, and reperfused myocardium and may therefore be helpful for the early detection of reperfusion following thrombolytic therapy for acute myocardial infarction.