RF Surface Coil Research Articles

Robust dual-angle measurement in magnetization transfer spectroscopy by time-optimal control.

Magnetization transfer spectroscopy relies heavily on the robust determination of relaxation times of nuclei participating in metabolic exchange. Challenges arise due to the use of surface RF coils for transmission (high variation) and the broad resonance band of most X nuclei. These challenges are particularly pronounced when fast mapping methods, such as the dual-angle method, are employed. Consequently, in this work, we develop resonance offset and robust excitation RF pulses for 31P magnetization transfer spectroscopy at 7T through ensemble-based time-optimal control. In our approach, we introduce a cost functional for designing robust pulses, incorporating the full Bloch equations as constraints, which are solved using symmetric operator splitting techniques. The optimal control design of the RF pulses developed demonstrates improved accuracy, desired phase properties, and reduced RF power when applied to dual-angle mapping, thereby improving the precision of exchange-rate measurements, as demonstrated in a preclinical in vivo study quantifying brain creatine kinase activity.

Hyperpolarized 15N caffeine, a potential probe of liver function and perfusion.

To demonstrate hyperpolarization of 15N-caffeine and report exploratory findings as a potential probe of liver function and perfusion. An amorphous formulation of [1,3-15N2]caffeine was developed for hyperpolarization via dissolution dynamic nuclear polarization. Polarizer hardware was augmented to support monitoring of solid-state 15N MR signals during the buildup of hyperpolarization. Liquid state hyperpolarized 15N MR signals were obtained in a preclinical 3T magnet by interfacing an external spectrometer console with home-built RF surface coils. 15N signal decay constants were estimated in H2O and in vivo in liver and brain regions of rats at 3 T. Decays were also measured at 9.4 T to assess the effect of B0, and in the presence of albumin to assess the impact of protein binding. Polarization levels of 3.5% and aqueous T1 relaxation times of nearly 200 s were attained for both N1and N3 positions at 3 T. Shorter apparent decay constants were observed in vivo, ranging from 25 s to 43 s, with modest extensions possible by exploiting competitive binding of iophenoxate with plasma albumin. Downstream products of caffeine could not be detected on in vivo 15N-MR spectra of the liver region, even with metabolic stimulation by -naphthoflavone treatment. Considering the high perfusion rate of brain, persistence of caffeine signal in this region is consistent with potential value as a perfusion imaging agent. These results establish the feasibility of hyperpolarization of hyperpolarized 15N-caffeine, but further work is necessary to establish the role of this new agent to probe liver metabolism and perfusion.

External waveguide magnetic resonance imaging for lower limbs at 3 T.

We report a method based on the traveling-wave MRI approach, in order to acquire images of human lower limbs with an external waveguide at 3T. We use a parallel-plate waveguide and an RF surface coil for reception, while a whole-body birdcage is used for transmission. The waveguide and the surface coil are located right outside the magnet, in the magnetic resonance (MR) conditional devices zone. We ran numerical simulations to investigate the field generated by the surface coil located at one of the waveguides, as well as a saline-solution phantom positioned on the opposite side (150cm away) inside the magnet. We obtained phantom images by varying the distance between the coil and the phantom, in order to investigate the signal-to-noise ratio and to validate our numerical simulations. Lower limb images of a healthy volunteer were also acquired, demonstrating the viability of this approach. Standard pulse sequences were used and no physical modifications were made to the MR imager. These numerical and experimental results show that traveling-wave MRI can produce high-quality images with only a simple waveguide and an RF coil located outside the magnet. This can be particularly favorable when acquiring images of lower limbs requiring a larger field ofview.

A Novel Energy Harvesting Circuit for RF Surface Coils in the MRI System.

RF surface coils are commonly used as receivers in Magnetic Resonance Imaging (MRI) systems to acquire sensitive signals from the human body. These coils rely on cables for power and transferring information from the patient to the computer for processing. Higher image quality and faster scan times are possible by using an array of surface coils, and there is a constant need for high-density surface coil arrays. Each array element utilizes at least three cables and, increasing the number of elements in the array also increases the number of cables, making the cable bundle bulkier. This makes the placement of cables complicated for the operators and may cause patient harm when improperly positioned. Wireless technologies can eliminate cables, and this paper proposes a novel design for harvesting the ambient RF energy present during the transmit phase of the MRI system operation. After introducing the surface coil's building blocks, the importance of the decoupler as a mechanism for safety and image quality is detailed. The paper presents the analysis and design of an RF energy harvesting circuit that couples to the decoupler circuit. Its performance is tested both in simulation and the Philips Ingenia 3.0 T MRI system. The results show that the circuit successfully harvests energy, up to 1 W, during the MRI's transmit phase without any adverse effects on the decoupler or surface coil. To make energy harvesting (EH) beneficial, a new GaN -based FET switch that consumes low power is also proposed.

Comparison of hyperpolarized 13 C and non-hyperpolarized deuterium MRI approaches for imaging cerebral glucose metabolism at 4.7 T.

The purpose of this study was to directly compare two isotopic metabolic imaging approaches, hyperpolarized (HP) 13 C MRI and deuterium metabolic imaging (DMI), for imaging specific closely related segments of cerebral glucose metabolism at 4.7 T. Comparative HP-13 C and DMI neuroimaging experiments were conducted consecutively in normal rats during the same scanning session. Localized conversions of [1-13 C]pyruvate and [6,6-2 H2 ]glucose to their respective downstream metabolic products were measured by spectroscopic imaging, using an identical 2D-CSI sequence with parameters optimized for the respective experiments. To facilitate direct comparison, a pair of substantially equivalent 2.5-cm double-tuned X/1 H RF surface coils was developed. For improved results, multidimensional low-rank reconstruction was applied to denoise the raw DMI data. Localized conversion of HP [1-13 C]pyruvate to [1-13 C]lactate, and [6,6-2 H2 ]glucose to [3,3-2 H2 ]lactate and Glx-d (glutamate and glutamine), was detected in rat brain by spectroscopic imaging at 4.7 T. The SNR and spatial resolution of HP-13 C MRI was superior to DMI but limited to a short time window, whereas the lengthy DMI acquisition yielded maps of not only lactate, but also Glx production, albeit with relatively poor spectral discrimination between metabolites at this field strength. Across the individual rats, there was an apparent inverse correlation between cerebral production of HP [1-13 C]lactate and Glx-d, along with a trend toward increased [3,3-2 H2 ]lactate. The HP-13 C MRI and DMI methods are both feasible at 4.7 T and have significant potential for metabolic imaging of specific segments of glucose metabolism.

Impact of a parallel magnetic field on radiation dose beneath thin copper and aluminum foils

Purpose: The RF coils for magnetic resonance image guided radiotherapy (MRIgRT) may be constructed using thin and/or low-density conductors, along with thinner enclosure materials. This work measures the surface dose increases for lightweight conductors and enclosure materials in a magnetic field parallel to a 6 MV photon beam. Methods: Aluminum and copper foils (9–127 μm thick), as well as samples of polyimide (17 μm) and polyester (127 μm) films are positioned atop a polystyrene phantom. A parallel plate ion chamber embedded into the top of the phantom measures the surface dose in 6 MV photon beam. Measurements (% of dose at the depth of maximum dose) are performed with and without a parallel magnetic field (0.22T at magnet center). Results: In the presence of a magnetic field, the unobstructed surface dose is higher (31.9%Dmax versus 22.2%Dmax). The surface dose is found to increase linearly with thickness for thin (<25 μm) copper (0.339%Dmaxμm−1) and aluminum (0.116%Dmaxμm−1) foils. In the presence of a magnetic field the slope is lower (copper: 0.16%Dmaxμm−1, aluminum: 0.06%Dmaxμm−1). The effect of in-beam foils is reduced due to partial shielding of the surface from contaminant electrons. Copper causes a surface dose increase ≈3 times higher than aluminum of the same thickness, consistent with their relative electron density. Polyester film (127μm) increases the surface dose (to 35% Dmax with field) about as much as a gown (36% Dmax with field), while the increase with polyimide film (17μm) is less than 1% above the open field dose. Conclusions: Thin copper and aluminum conductors increase surface dose by an amount comparable to a hospital gown. Similarly, enclosure materials made of thin polyester or polyimide film increase surface dose by only a few %Dmax in excess of an unobstructed beam. Based on measurements in this study, in-beam, surface RF coils are feasible for MRIgRT systems.

NMR 센서용 자석과 고주파 코일 기술

화학, 의학, 물리, 생물 등 다양한 분야에서 활용도가 높지만 거대한 자석과 제어장치로 인해 휴대할 수 없는 NMR 장치를 소형 센서로 제작하기 위한 기본 개념을 제시하고, NMR 센서 프로브의 구성 요소인 자석과 고주파 코일의 전산모사와 실제 설계, 제작을 통해 기본적인 특성을 살펴보았다. Nd-Fe-B 희토류 영구 자석은 직경 3~6 mm, 높이 1~7 mm의 다양한 크기로 제작하여 크기에 따른 자기장 세기를 조사하였다. CMOS 공정을 적용한 원형의 면-코일은 Al-1%Si 금속을 증착, 패턴닝 후 400°C에서 열처리하여 제작하였으며, 선폭 10 μm, 간격 2 μm, 외경 ~0.4 mm 크기로 제작되었고, 10.47 MHz에서 8.7 Ω/mm의 높은 저항 임피던스와 낮은 Q 값 ( 1)이 측정되었다. 한편, PCB 기술로 제작한 PCB 면-코일은 선폭 100 μm 이상, 외경 약 2 mm로 제작되었고, 10.27 MHz에서 1 Ω 이하의 낮은 저항 임피던스와 4.85±0.18의 Q 값을 갖는 것으로 평가되었다.

Local Multi-Channel RF Surface Coil versus Body RF Coil Transmission for Cardiac Magnetic Resonance at 3 Tesla: Which Configuration Is Winning the Game?

IntroductionThe purpose of this study was to demonstrate the feasibility and efficiency of cardiac MR at 3 Tesla using local four-channel RF coil transmission and benchmark it against large volume body RF coil excitation.MethodsElectromagnetic field simulations are conducted to detail RF power deposition, transmission field uniformity and efficiency for local and body RF coil transmission. For both excitation regimes transmission field maps are acquired in a human torso phantom. For each transmission regime flip angle distributions and blood-myocardium contrast are examined in a volunteer study of 12 subjects. The feasibility of the local transceiver RF coil array for cardiac chamber quantification at 3 Tesla is demonstrated.ResultsOur simulations and experiments demonstrate that cardiac MR at 3 Tesla using four-channel surface RF coil transmission is competitive versus current clinical CMR practice of large volume body RF coil transmission. The efficiency advantage of the 4TX/4RX setup facilitates shorter repetition times governed by local SAR limits versus body RF coil transmission at whole-body SAR limit. No statistically significant difference was found for cardiac chamber quantification derived with body RF coil versus four-channel surface RF coil transmission. Our simulation also show that the body RF coil exceeds local SAR limits by a factor of ~2 when driven at maximum applicable input power to reach the whole-body SAR limit.ConclusionPursuing local surface RF coil arrays for transmission in cardiac MR is a conceptually appealing alternative to body RF coil transmission, especially for patients with implants.

TH-AB-BRA-12: Experimental Results From the First High-Field Inline MRI-Linac

Purpose: The pursuit of real-time image guided radiotherapy using optimal tissue contrast has seen the development of several hybrid MRI-treatment systems, high field and low field, and inline and perpendicular configurations. As part of a new MRI-Linac program, an MRI scanner was integrated with a linear accelerator to enable investigations of a coupled inline MRI-Linac system. This work describes our experimental results from the first high-field inline MRI-Linac. Methods: A 1.5 Tesla magnet (Sonata, Siemens) was located in a purpose built RF cage enabling shielding from and close proximity to a linear accelerator with inline orientation. A portable linear accelerator (Linatron, Varian) was installed together with a multi-leaf collimator (Millennium, Varian) to provide dynamic field collimation and the whole assembly built onto a stainless-steel rail system. A series of MRI-Linac experiments was performed to investigate: (1) image quality with beam on measured using a macropodine (kangaroo) ex vivo phantom; (2) the noise as a function of beam state measured using a 6-channel surface coil array and; (3) electron focusing measured using GafChromic film. Results: (1) The macropodine phantom image quality with the beam on was almost identical to that with the beam off. (2) Noise measured with a surface RF coil produced a 25% elevation of background noise when the radiation beam was on. (3) Film measurements demonstrated electron focusing occurring at the center of the radiation field. Conclusion: The first high-field MRI-Linac has been built and experimentally characterized. This system has allowed us to establish the efficacy of a high field in-line MRI-Linac and study a number of the technical challenges and solutions. Supported by the Australian National Health and Medical Research Council, the Australian Research Council, the Australian Cancer Research Foundation and the Health and Hospitals Fund.

Design and Development of a General‐Purpose Transmit/Receive (T/R) Switch for 3T MRI, Compatible for a Linear, Quadrature and Double‐Tuned RF Coil

AbstractThis work presents the design and development of a general‐purpose T/R switch for MR imaging and spectroscopy, compatible with single and double‐tuned RF coils using linear, quadrature, or both modes at a low cost and with minimum development time using simple electronic circuits. This T/R switch was demonstrated with a custom double‐tuned 1H/31P transmit receive surface RF coils built for 31P MRS of a lamb's heart with surgically created congenital heart defects. Two passive trap circuits tuned to 1H and 31P frequencies fed from a common drive point were built to filter two different frequency T/R switches. The T/R switch was built for a 1H linear RF coil and 31P quadrature RF coil. This T/R switch design is easily modifiable to linear, quadrature and double‐tuned RF coils of relatively wide range of frequencies, so as to enable imaging of proton and X‐nuclei at 3T field. The performance of the custom T/R switch was tested with bench measurements of its isolation, insertion loss and switching time, under pulsed conditions, and on a phantom with a 3T magnet by comparing the signal‐to‐noise ratio with a commercial T/R switch. A high isolation, low insertion loss and fast switching time in the range of nanoseconds were obtained on the bench. Identical isolation was observed under pulsed conditions. An improvement of about 29% gain in signal‐to‐noise ratio was obtained with this T/R switch compared to the commercial T/R switch.

An adaptive diffusion-weighted whole-body magnetic resonance imaging scheme using the multistation approach

Whole-body diffusion-weighted imaging (DWI) is a useful tool in oncology, which enables fast screening of disseminated tumors, lymph nodes or abscesses in the body. Multistation magnetic resonance imaging (MRI) or continuously moving table (CMT) MRI can be performed to overcome the limited field of view (FOV) of the magnet bore in whole-body DWI. Although CMT-MRI is regarded as a more advanced form of whole-body MRI, it cannot be widely used because most of the available MR systems are not equipped with the required hardware/software to perform CMT. Thus, optimizing the multistation approach for whole-body DWI, which is more widely available and easier to perform with the existing MR systems, is worthwhile. To improve the quality of DW images acquired with the multistation approach, we used different combinations of the built-in body RF coil and the phased-array surface RF coils for reception of the signals in whole-body DWI in this work. If different coils are selectively used in the extended FOV and appropriate reconstruction algorithms are exploited, the screening ability of whole-body DWI can be improved while minimizing the patient’s discomfort and the artifacts due to physiological motions.

SU‐E‐J‐239: Influence of RF Coil Materials On Surface and Buildup Dose From a 6MV Photon Beam

Purpose:In order to perform real time tumour tracking using an integrated Linac‐MR, images have to be acquired during irradiation. MRI uses RF coils in close proximity to the imaged volume. Given current RF coil designs this means that the high energy photons will be passing through the coil before reaching the patient. This study experimentally investigates the dose modifications that occur due to the presence of various RF coil materials in the treatment beam.Methods:Polycarbonate, copper or aluminum tape, and Teflon were used to emulate the base, conductor and cover respectively of a surface RF coil. These materials were placed at various distances from the surface of polystyrene or solid water phantoms which were irradiated in the presence of no magnetic field, a transverse 0.2T magnetic field, and a parallel 0.2T magnetic field. Percent depth doses were measured using ion chambers.Results:A significant increase in surface and buildup dose is observed. The surface dose is seen to decrease with an increasing separation between the emulated coil and the phantom surface, when no magnetic field is present. When a transverse magnetic field is applied the surface dose decreases faster with increasing separation, as some of the electrons created in the coil are curved away from the phantom's surface. When a parallel field is present the surface dose stays approximately constant for small separations, only slightly decreasing for separations greater than 5cm, since the magnetic field focuses the electrons produced in the coil materials not allowing them to scatter.Conclusion:Irradiating a patient through an RF coil leads to an increase in the surface and buildup doses. Mitigating this increase is important for the successful clinical use of either a transverse or a parallel configuration Linac‐MR unit.This project is partially supported by an operating grant from the Canadian Institute of Health Research (CIHR MOP 93752)

Determination of position and shape of flexible mri surface coils using the Microsoft Kinect for attenuation correction in PET/MRI.

Due to the varying position and shape of flexible MRI RF surface coils, the creation of attenuation maps for these coils is a challenging task. Nevertheless, coil material (metal, plastic, rubber) attenuates the PET signal to a considerable amount. Thus, including a coil μ-map into the human μ-map is essential. In this work, we present a method to determine the position and shape of flexible coils with the help of the Microsoft Kinect depth camera. Phantom PET/MRI (Siemens Biograph mMR) and CT scans (Siemens Biograph mCT) were performed with and without the flexible 32-channel coil equipped with 15 markers visible in CT and Kinect. Prior to the PET/MRI acquisition, Kinect data is acquired of the phantom with the coil on top. The manually extracted marker positions from CT and Kinect are used to non-rigidly transform the template CT according to the Kinect marker positions describing the shape of the coil during PET/MRI acquisition. An appropriate μ-map can then be calculated from the transformed CT dataset. Subsequently, the μ-map is placed in relation to the patient table according to the Kinect-derived marker positions. First results show that the coil shape can be determined with the help of the Kinect camera. The transformation of the template CT dataset according to Kinect marker positions during PET/MRI leads to appropriate results. Furthermore, the position of the coil can also be determined for an accurate placement of the μ-map in relation to the patient table. The determination of position and shape of flexible surface coils using the Kinect camera can be a way to include the CT-based coil μ-map in PET/MRI acquisitions without the need for additional MRI scans. Accuracy and practicability of the method have to be tested in further experiments.

Eight-channel transceiver RF coil array tailored for ¹H/¹⁹F MR of the human knee and fluorinated drugs at 7.0 T.

The purpose of this study was to evaluate the feasibility of an eight-channel dual-tuned transceiver surface RF coil array for combined (1)H/(19)F MR of the human knee at 7.0 T following application of (19)F-containing drugs. The (1)H/(19)F RF coil array includes a posterior module with two (1)H loop elements and two anterior modules, each consisting of one (1)H and two (19)F elements. The decoupling of neighbor elements is achieved by a shared capacitor. Electromagnetic field simulations were performed to afford uniform transmission fields and to be in accordance with RF safety guidelines. Localized (19)F MRS was conducted with 47 and 101 mmol/L of flufenamic acid (FA) – a (19)F-containing non-steroidal anti-inflammatory drug – to determine T1 and T2 and to study the (19)F signal-to-dose relationship. The suitability of the proposed approach for (1)H/(19)F MR was examined in healthy subjects. Reflection coefficients of each channel were less than -17 dB and coupling between channels was less than -11 dB. Q(L)/Q(U) was less than 0.5 for all elements. MRS results demonstrated signal stability with 1% variation. T1 and T2 relaxation times changed with concentration of FA: T1 /T2 = 673/31 ms at 101 mmol/L and T1 /T2 = 616/26 ms at 47 mmol/L. A uniform signal and contrast across the patella could be observed in proton imaging. The sensitivity of the RF coil enabled localization of FA ointment administrated to the knee with an in-plane spatial resolution of (1.5 × 1.5) mm(2) achieved in a total scan time of approximately three minutes, which is well suited for translational human studies. This study shows the feasibility of combined (1)H/(19)F MRI of the knee at 7.0 T and proposes T1 and T2 mapping methods for quantifying fluorinated drugs in vivo. Further technological developments are necessary to promote real-time bioavailability studies and quantification of (19)F-containing medicinal compounds in vivo.

Design and analysis of matching network for stepped impedance structured 1.5 Tesla magnetic resonance imaging RF surface coil

In this paper a new impedance matching technique is proposed to improve the return loss performance of the stepped impedance 1.5 Tesla Magnetic Resonance Imaging (MRI) RF coil. Recently the concepts of stepped impedance microstrip transmission line sections were used in MRI RF volume coil developments. In this paper to further advance this approach a Stepped Impedance Structure (SIS) is focused for surface type RF coils along with suitable impedance matching network. The matching network consists of a lumped capacitor and inductor forming an L shaped structure. The quality factor based design procedure is followed to determine the value of matching network components. The performance of L section design is verified for different SIS RF coil width values. A performance comparison of L section matching network for different SIS RF coil width values is also presented. The workability of the proposed matching network has been verified using Advanced Design System (ADS) S-parameter simulation results.

MR-monitored focused ultrasound using the acoustic-coupling water bath as an intrinsic high-mode dielectric resonator.

The conventional set-up for MR-monitored focused ultrasound surgery includes a piezoelectric transducer and an acoustic-coupling water bath integrated into the MR patient table; a large surface RF coil is placed close to the patient or, alternatively, the body coil is used as the MR receiver. Potential disadvantages of this approach are that the body coil has low sensitivity because of its low filling factor and the local RF coil can interfere with and cause reflections of the ultrasound irradiation. In this article, a completely new approach is presented, in which an MR transmit/receive coil is not needed at all. Instead, the dimensions of the water bath are adjusted so that a high-order dielectric mode is excited, resulting in efficient MR excitation and reception at the transducer focal point. An example of monitoring ultrasound-mediated heating in a phantom is shown on a 7-T human system, although the new method can also be applied at lower fields.

Computer-aided design and analysis of surface type RF coil for 1.5 tesla magnetic resonance imaging applications

Magnetic Resonance Imaging (MRI) technique is widely used to capture the images of the liquid items inside the human body. In this work, a microstrip-based surface type RF radiating coil is proposed for 1.5 tesla MRI. The design involves the determination of inductive reactance for the selected coil geometry using Advanced Design System (ADS) smith chart utility. The resonance capacitor value is selected to make the coil resonance frequency exactly at 63.85 MHz. The coil will have an external matching and tuning capacitors to compensate for the mutual coupling effect of near field radiation. An FR4 (Flame Retardant type 4 Epoxy) substrate having a thickness of 1.6 mm is selected to construct the microstrip-based RF surface coil. Return loss behaviour of the proposed 1.5 tesla 2L section RF coil has been compared with 1.5 tesla 4L section and 7 tesla 4L section RF coils using ADS 2011 S parameter simulation.

An embedded four‐channel receive‐only RF coil array for fMRI experiments of the somatosensory pathway in conscious awake marmosets

fMRI has established itself as the main research tool in neuroscience and brain cognitive research. The common marmoset (Callithrix jacchus) is a non-human primate model of increasing interest in biomedical research. However, commercial MRI coils for marmosets are not generally available. The present work describes the design and construction of a four-channel receive-only surface RF coil array with excellent signal-to-noise ratio (SNR) specifically optimized for fMRI experiments in awake marmosets in response to somatosensory stimulation. The array was designed as part of a helmet-based head restraint system used to prevent motion during the scans. High SNR was obtained by building the coil array using a thin and flexible substrate glued to the inner surface of the restraint helmet, so as to minimize the distance between the array elements and the somatosensory cortex. Decoupling between coil elements was achieved by partial geometrical overlapping and by connecting them to home-built low-input-impedance preamplifiers. In vivo images show excellent coverage of the brain cortical surface with high sensitivity near the somatosensory cortex. Embedding the coil elements within the restraint helmet allowed fMRI data in response to somatosensory stimulation to be collected with high sensitivity and reproducibility in conscious, awake marmosets.

216 IMPAIRED IN VIVO MITOCHONDRIAL KREBS CYCLE ACTIVITY FOLLOWING MYOCARDIAL INFARCTION ASSESSED USING HYPERPOLARIZED MAGNETIC RESONANCE SPECTROSCOPY

An increasing body of evidence links alterations in cardiac metabolism with the progression of heart disease. Using the recently developed technique of hyperpolarized 13 C magnetic resonance spectroscopy, in vivo alterations in mitochondrial metabolism were assessed following myocardial infarction (MI). Hyperpolarization of 13C containing compounds can increase their signal by >10,000 fold over conventional methods. MI with reperfusion surgery was performed on eleven female Wistar rats. Four sham animals were also prepared. Animals were given two hyperpolarized scans, of either [1- 13 C] or [2- 13 C] pyruvate, at 1, 6 and 22 weeks post-MI. [1- 13 C] or [2- 13 C] pyruvate were hyperpolarized and dissolved in a GE prototype polarizer. 1ml of 80mM hyperpolarized pyruvate was injected over 10s via a tail vein catheter into an anaesthetised rat positioned in a 7T MR scanner. Spectra were acquired every second for a 1min following injection, using a 5 o RF excitation pulse. Signal was localised to the heart using a custom 13 C RF surface coil. Metabolic alterations were correlated with ejection fraction (EF) assessed by echocardiography, at each timepoint to yield information on the interplay between cardiac function and mitochondrial metabolism. One week post-MI, there were no detectable alterations in in vivo cardiac mitochondrial metabolism over the range of EFs observed. This is an early adaptive phase post-MI, where scar formation and remodelling of the heart are occurring. Six weeks post-MI, a novel finding in this study was impaired in vivo mitochondrial Krebs cycle activity, in addition to decreased flux into acetylcarnitine, which correlated with the EF. These changes were seen in the absence of any alterations in pyruvate dehydrogenase (PDH) flux. Thus, in vivo alterations in Krebs cycle flux may indicate an early maladaptive phase in the metabolic derangement following MI. By 22 weeks post-MI, alterations were also seen in PDH flux, which positively correlated with EF, highlighting a reduction in glucose oxidation and Krebs cycle activity in the infarcted heart. At 22 weeks, biochemical analysis was performed on excised hearts, to further characterize the metabolic alterations accompanying MI. Enzyme activities of PDH, citrate synthase, isocitrate dehydrogenase and carnitine acetyltransferanse positively correlated with EF. Metabolomic analysis revealed reduced levels of Kerbs cycle intermediates. The correlation between function and metabolism raises an interesting paradox; is the reduction in PDH and Krebs cycle activity due to a reduction in contraction and therefore a reduced energy requirement, or does the altered PDH and Krebs cycle activity lead to reduced energy levels meaning cardiac contraction is impaired? This study highlights the importance of assessing metabolism at multiple timepoints in vivo , and demonstrates the potential of hyperpolarized MRS for investigating the metabolic effects of progressive diseases, potentially in a clinical setting.

219 PPAR-ALPHA KNOCKOUT LEADS TO AN AGE-INDUCED INCREASE IN IN VIVO PYRUVATE DEHYDROGENASE FLUX

<h3>Introduction</h3> Peroxisome proliferator-activated receptors (PPARα, β/δ, γ) are important regulators of cardiac fatty acid metabolism. PPARα has the highest binding affinity for fatty acids and is the dominant cardiac PPAR isoform. The PPARα knockout mouse has been extensively used to investigate the role of PPARα in metabolism and disease. This study aimed to understand the role of PPARα in the aging heart, through assessment of the metabolism of [1–13C] pyruvate, using hyperpolarisation by dynamic nuclear polarisation (DNP). <h3>Methods</h3> <i>Animals-</i> Six young (3–4 months) and six old (20–22 months) controls (129SvEv) and five young (3–4 months) and six old (20–22 months) PPARα-KO mice (on a 129SvEv background) received a hyperpolarised scan, performed between 7 am and 11 am, while mice were in the fed state. <h3>Hyperpolarised 13C MRS Protocol</h3> [1–13C] pyruvate was hyperpolarised and dissolved as previously described. An aliquot of 0.15 ml of 80 mM hyperpolarised [1–13C] pyruvate solution was injected over 10 s via a tail vein catheter into an anaesthetised mouse, positioned in a 7 T MR scanner. Spectra were acquired for 1 min following injection, with 1 s temporal resolution, using a 15° RF excitation pulse. Signal was localised to the heart using a home-built 13C RF surface coil. Quantified peak areas were input into a kinetic model, described by Atherton et al, and plotted against time. The rate of exchange of the 13C label between pyruvate and its metabolites was termed 13C label incorporation. 13C label incorporation into the bicarbonate pool has been used as a measure of pyruvate dehydrogenase (PDH) flux in the rat. <h3>Biochemical analysis</h3> Protein levels of glucose transporter (GLUT) 4, medium chain acyl-CoA dehydrogenase (MCAD), PDH kinase (PDK) 2 and PDK4 were measured in cardiac tissue by western blotting. PPARα mRNA levels were assessed using qRT-PCR. <h3>Results</h3> Young and old PPARα-KO hearts had significantly decreased PPARα mRNA levels relative to controls and a 59% decrease in protein levels of the PPARα target gene, MCAD. Cardiac PDH flux did not differ between young control and PPARα-KO mice, but in old PPARα-KO mice, PDH flux was increased by 96% relative to controls. Analysis of cardiac metabolic proteins revealed a 141% increase in GLUT4 expression in old PPARα-KO mice. There were no differences in PDK2 or PDK4 protein levels, suggesting that the increased PDH flux in aged PPARα-KO mice was not mediated by altered PDH phosphorylation. <h3>Conclusions</h3> Aged PPARα-KO mice exhibited increased cardiac PDH flux relative to young and old control mice. This may be mediated by increased GLUT4 protein levels, which would facilitate glucose uptake and glycolysis. No changes in PDK2 and PDK4 expression were observed, although the enzymatic activities of these proteins were not examined.