Janusz H. Hankiewicz

Early impairment of transmural principal strains in the left ventricular wall after short-term, high-fat feeding of mice predisposed to cardiac steatosis.

Background—Myocardial lipid accumulation precedes some cardiomyopathies, but little is known of concurrent effects on ventricular mechanics. We tested the hypothesis that intramyocardial lipid accumulation during a short-term, high-fat diet (HFD) affects 2-dimensional strains in the heart. We examined the hearts of nontransgenic (NTG) mice and of transgenic mice predisposed to elevated triacylglyceride (TAG) storage linked to low-level overexpression of peroxisome proliferator activated receptor (PPAR-&agr;). Methods and Results—Myocardial lipid and transmural principal strains E1 and E2 were determined in vivo with 1H magnetic resonance spectroscopy/imaging before and after 2 weeks of an HFD in both PPAR-&agr; and NTG littermate mice. Baseline lipid was elevated in PPAR-&agr; compared with NTG mice. An HFD increased mobile lipid by 174% in NTG mice (P<0.05) and by 79% in PPAR-&agr; mice (P<0.05). After an HFD, lipid and TAG were higher in PPAR-&agr; versus NTG mice by 63% and 81%, respectively. However, TAG in PPAR-&agr; mice after an HFD was similar to TAG in PPAR-&agr; mice fed a regular diet, suggesting that the magnetic resonance spectroscopy signal from lipid is not exclusive to TAG. Only at the highest lipid contents, achieved in PPAR-&agr; mice, were strains affected. Endocardial strain was most compromised, with a negative correlation to lipid (P<0.05). Conclusions—A short-term HFD elevated myocardial lipid measures as determined by magnetic resonance spectroscopy, which became dissociated from TAG content in hearts predisposed to cardiac steatosis. The increased lipid was associated with concurrent, transmural reductions in E1 and E2 strains across the left ventricular wall. Strains were attenuated at the highest levels of lipid accumulation, suggesting a threshold response. Thus, 2-dimensional strains are impaired early and without left ventricular diastolic dysfunction, owing to cardiac steatosis.

17O magnetic resonance imaging of the human brain

Abstract Here we show the first example of in vivo oxygen-17 (17O) magnetic resonance imaging of the human in natural abundance. Two-dimensional fast multi-planar gradient recalled 90 deg echo (FMPGR/90) pulse sequence and three-dimensional projection reconstruction pulse sequence methods were used.

Improved Cardiac Tagging Resolution at Ultra-High Magnetic Field Elucidates Transmural Differences in Principal Strain in the Mouse Heart and Reduced Stretch in Dilated Cardiomyopathy

Cardiac tagging resolution for regional principal strains E1 and E2 has been a limiting factor for the study of dilated mouse hearts, in which the left ventricle (LV) wall thickness can drop to below 1 mm. Therefore, high resolution tagging was performed at 14.1 T to enable transmural principal strain measurements across the LV wall of normal mouse hearts and average principal strains in thinned LV walls of a transgenic mouse (PKCepsilon TG) that develops dilated LV. A modified DANTE tagging and fast gradient imaging method produced a tagging grid dimension of 0.33 x 0.33 mm and line thickness under 0.1 mm. In normal mice, average E1 strain in the epicardium was significantly higher than the endocardial E1 (epi = 0.22 +/- 0.10; endo = 0.13 +/- 0.07, p < 0.05), while magnitude of average endocardial E2 was greater than in the epicardium (endo = -0.12 +/- 0.03, epi = -0.08 +/- 0.03; p < 0.001). E1 strain averaged over four segments was reduced in dilated hearts compared to controls (PKCepsilon TG = 0.14 +/- 0.02; control = 0.18 +/- 0.02, p < 0.01), with specific reductions in septal (33%) and lateral (31%, p < 0.01) segments. E2 strain was similar between dilated and control hearts at -0.11 +/- 0.01. Thus, improved tagging resolution demonstrates that stretch (E1), but not compression strains (E2), are reduced as a result of significant LV wall thinning in a mouse model of dilated cardiomyopathy.

Ferromagnetic particles as magnetic resonance imaging temperature sensors

Magnetic resonance imaging is an important technique for identifying different types of tissues in a body or spatial information about composite materials. Because temperature is a fundamental parameter reflecting the biological status of the body and individual tissues, it would be helpful to have temperature maps superimposed on spatial maps. Here we show that small ferromagnetic particles with a strong temperature-dependent magnetization, can be used to produce temperature-dependent images in magnetic resonance imaging with an accuracy of about 1 °C. This technique, when further developed, could be used to identify inflammation or tumours, or to obtain spatial maps of temperature in various medical interventional procedures such as hyperthermia and thermal ablation. This method could also be used to determine temperature profiles inside nonmetallic composite materials.

Zinc doped copper ferrite particles as temperature sensors for magnetic resonance imaging

We investigate the use of Cu0.35Zn0.65Fe2O4 particles as temperature-dependent sensors in magnetic resonance imaging (MRI). This material has a Curie temperature near 290 K, but in the large magnetic fields found in MRI scanners, there is a significant temperature-dependent magnetic moment near body temperature; 310 K. When the ferrite particles are doped into an agar gel, the temperature-dependent magnetic moment leads to a temperature-dependent broadening of the NMR linewidth for water protons and to a temperature-dependent image intensity for MRI, allowing one to make temperature maps within objects. The temperature resolution is about 1.3 K.

Development of a ring PET insert for MRI

Our research group constructed a 12-module PET detection ring composed of Hamamatsu multi-pixel photon counter (MMPC) silicon photomultiplier (SiPM) detectors placed in a ring that is fully MRI compatible. This brain imager can be placed around the head of a patient (clinical setting) or subject (research setting) and allow for comfortable upright imaging. However, an alternative way to use this device, as enabled by the technology, is to indeed scan individuals in the supine position in conjuncture with current MRI systems. This PET prototype is able to image simultaneously as the MRI scan is occurring, thus maximizing co-registration and the accuracy of the assignment of metabolically active voxels to their anatomically correct counterparts as identified by the MR image. In this study, we first conducted some basic instrumentation tests to ensure the device was functioning properly outside of the MRI, and additionally scan some phantoms (Derenzo; Hoffman Brain) to assess the quality in which our brain imager is able to produce adequate images. After these initial studies, we conducted multiple different experiments inside a 3 Tesla MRI in order to see how the magnetic field would influence the operation of the PET imager and vice versa. Through simultaneous PET/MRI scanning of a Hoffman brain phantom filled with F18 radioactivity and water, it was shown that the quality of the MR image was largely unaffected by the PET imager. Furthermore, although the quality of PET imaging was affected by the RF pulsing, an acceptable PET image was nevertheless produced. As we discuss following the results, the success of this study shows that our brain imager is indeed MR compatible, and that next generation devices based on its concepts will continue to improve combined PET/MRI functionality. As two of the major advantages of this imager are the potential for low-dose scanning and its adaptability to any MRI scanner, this study suggests that PET/MRI brain imaging with low dose is in principle possible using an insert which could be adapted to any MRI scanner, using standard RF coils for that scanner.

Early Impairment of Transmural Principal Strains in the Left Ventricle Wall Following Short-Term, High Fat Feeding of Mice Predisposed to Cardiac Steatosis

Background—Myocardial lipid accumulation precedes some cardiomyopathies, but little is known of concurrent effects on ventricular mechanics. We tested the hypothesis that intramyocardial lipid accumulation during a short-term, high-fat diet (HFD) affects 2-dimensional strains in the heart. We examined the hearts of nontransgenic (NTG) mice and of transgenic mice predisposed to elevated triacylglyceride (TAG) storage linked to low-level overexpression of peroxisome proliferator activated receptor (PPAR-&agr;). Methods and Results—Myocardial lipid and transmural principal strains E1 and E2 were determined in vivo with 1H magnetic resonance spectroscopy/imaging before and after 2 weeks of an HFD in both PPAR-&agr; and NTG littermate mice. Baseline lipid was elevated in PPAR-&agr; compared with NTG mice. An HFD increased mobile lipid by 174% in NTG mice (P<0.05) and by 79% in PPAR-&agr; mice (P<0.05). After an HFD, lipid and TAG were higher in PPAR-&agr; versus NTG mice by 63% and 81%, respectively. However, TAG in PPAR-&agr; mice after an HFD was similar to TAG in PPAR-&agr; mice fed a regular diet, suggesting that the magnetic resonance spectroscopy signal from lipid is not exclusive to TAG. Only at the highest lipid contents, achieved in PPAR-&agr; mice, were strains affected. Endocardial strain was most compromised, with a negative correlation to lipid (P<0.05). Conclusions—A short-term HFD elevated myocardial lipid measures as determined by magnetic resonance spectroscopy, which became dissociated from TAG content in hearts predisposed to cardiac steatosis. The increased lipid was associated with concurrent, transmural reductions in E1 and E2 strains across the left ventricular wall. Strains were attenuated at the highest levels of lipid accumulation, suggesting a threshold response. Thus, 2-dimensional strains are impaired early and without left ventricular diastolic dysfunction, owing to cardiac steatosis.

In vivo natural-abundance17O/1H MRI of rhesus monkey body in a whole-body scanner

In vivo natural-abundance17O and1H magnetic resonance imaging (MRI) techniques were combined to image the whole body of a rhesus monkey. The results demonstrate the feasibility of acquiring consecutive fast17O and1H images with a standard MRI scanner. The method has applications in the field of functional MRI and in17O MRI measurements of metabolism rate.

Combined17O/1H MRI study in a whole-body scanner

A simple method of obtaining consecutive1H and natural-abundance17O images is described with a scanner’s original body resonator (for1H) and a homemade linear birdcage (for17O). Two kinds of experiments were performed to test the method. In the first experiment, a proton image of the phantom was acquired with a whole-body resonator. In the second experiment, the phantom was inserted into an oxygen birdcage resonator and imaged again with a whole-body resonator. The intensities of images resulting from the experiments were analyzed. Although theB1 field homogeneity is disturbed, the proton images acquired with a whole-body resonator when the oxygen resonator is present are of acceptable quality for use in the combined17O/1H imaging.

Combined 1H MRI, PET and Multinuclear MRS hybrid imaging system

In this abstract we describe a novel method of combining three imaging modalities: 1H Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET), and multinuclear Magnetic Resonance Spectroscopy (MRS) in one system dedicated for true molecular imaging. The addition of PET to MRI was introduced to provide functional/metabolic information about diseases or natural processes in the human body. High resolution and soft tissue contrast of 1H MRI morphological images is complemented by PET’s ability to depict metabolic processes through the use of biologically active radioactively labeled imaging agents, paving the way for molecular imaging. The application of localized 1H MRS is implemented by using the imaging coil tuned to proton resonances. Localized, or MRI-guided, MR spectroscopy enables quantification of chemical composition of different tissue components in small volumes of less than 0.1 ml. Particularly in the brain, 1H MRS can for example measure accurately N-acetyl aspartate (NAA), lactate, glutamate, creatine, and choline to provide a view of the progression of neuro-degeneration. However, the use of coil exclusively tuned to 1H significantly limits the “window” of observation by elimination of other biologically relevant nuclei like 13C, 14N, 17O, or 31P. Therefore we propose introducing a second resonator that will be tuned to these nuclei. We anticipate that MRS of other than 1H nuclei will provide more spectroscopic details and remove the ambiguity that exists in the 1H spectra from overlapping lines. The additional coil tuned to specific X-nuclei can be embedded within the existing 1H coil or can be removable, to be added whenever MRS on these nuclei is deemed necessary.