MR Methods

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Our preclinical MR core facility offers a variety of advanced imaging methods, with a particular focus on the assessment of cardiac structure and function:

Index:
Cardiac Cinematographic (CINE) MRI
Late Gadolinium Enhancement (LGE)
Flow and Tissue Phase Mapping
T1 mapping
MR Spectroscopy
Fat Imaging
Neuroimaging
Ex-vivo
Ongoing research

Cardiac Cinematographic (CINE) MRI


Cardiac cine MRI is a widely used MR technique for making videos of the beating heart in vivo. It allows measurement of e.g. the mass and blood volumes of the heart. Importantly, cine MRI facilitates reliable measurement of the ventricular volumes throughout the entire cardiac cycle, which allows measurement of stroke volume (the ejected volume per heartbeat) and ejection fraction (the ratio of stroke volume and maximum volume). Cine MRI also allows rough assessment of the deformation of the heart, for instance wall thickening.



Related publications from the core facility:
Thienpont B. et al., J. Clin. Invest., 127(1), 335-348, (2017)
Zoccarato, A. et al., Circ. Res., 117(8), 707-19, (2015)


CINE of the beating mouse heart (IEMR)

Late Gadolinium Enhancement (LGE)

Late gadolinium enhanced (LGE)  Lili
LGE image of one day post-infarction rat (IEMR)


Both in patients and preclinical models, LGE Cardiac MRI provides a noninvasive phenotyping tool for accurate and easy detection and quantification of myocardial fibrosis by probing the retention of gadolinium-contrast agent in myocardial tissue. Late gadolinium enhancement (LGE) cardiac MRI has been used extensively in a large number of studies for the measurement of myocardial scarring. A contrast agent with gadolinium (Gd) diffuses rapidly out of capillaries and into tissue but cannot cross intact cell membranes. So, after an intra-venous or intraperitoneal bolus, both normal and abnormal myocardium passively accumulate Gd, but with time, because of slower kinetics and a larger volume of distribution, abnormal myocardium retains a slightly larger amount of Gd per unit volume. In an inversion-recovery T1-weighted image, regions with higher Gd related to areas of scarring and necrosis are revealed as bright spots.


Related publication from the core facility:
Olsen M. B. et al., Cell Reports, 18(1), 82-92, (2017)


Flow and Tissue Phase Mapping


Phase-contrast MRI is a versatile MRI technique which routinely is used to measure blood flow (flow-encoded MRI) or myocardial function (tissue phase mapping). Research at the Oslo Preclinical MRI group has focused at establishing phase-contrast MRI as a robust tool for measuring the regional function of the myocardium, in particular strain and work. Also, we have used phase-contrast MRI to assess the flow into the rat heart.



Related publications from the core facility:
Espe E.K. et al., Circ. Cardiovasc. Imaging, 8(2), (2015)
Espe E.K. et al., J. Cardiovasc. Magn. Reson., 15, 82, (2013)


PC-MRI strain and strain rate measurement of the beating rat heart (IEMR)


T1 mapping


Extracellular matrix remodeling is an essential biological process. Particularly, increased fibrotic growth is associated with stiffening of the ventricle, leading to diastolic, and eventually systolic, dysfunction. Detecting myocardial fibrosis is of importance for risk stratification, contributes to understanding the mechanisms responsible for fibrosis initiation, progression, and resolution, and, ultimately, allows for the design of new antifibrotic treatments. T1 mapping is a technique to quantify the exact T1 of the tissue. It also employs Gd based contrast agent. However, T1 mapping allows the detection of variations in gadolinium distribution within the tissue with higher resolution than replacement fibrosis imaging, i.e. LGE. Combining precontrast/native T1 and postcontrast T1, the extra cellular volume fraction can be calculated.


For more information about T1 mapping: Jellis, C. L., Kwon, D.H., Cardiovasc. Diagn. Ther., 4(2), 126-137, (2014)



MR spectroscopy

MRS_1
Image of 1D quantitative 31P spectroscopy from skeletal muscle of a rat (IEMR)

In addition to imaging methods for the assessment of cardiac structure, function and perfusion, localized spectroscopic methods have been developed to study the metabolism in the mouse heart in vivo. High-energy phosphates (HEPs), such as adenosine triphosphate (ATP) and phosphocreatine (PCr), are the chemical currency that pays for almost all of the energy-consuming processes within the body, particularly the heart. Several MRI and MRS studies have demonstrated that the normal cardiac PCr-to-ATP (PCr/ATP) ratio is reduced in chronic heart failure. 2D 31P chemical shift imaging (CSI) can yield a whole-heart metabolic profile in one scan with relatively high resolution. In addition, 1D 31P spectroscopy on skeletal muscle also provides the opportunity to quantify PCr and ATP in different disease animal models.


For more information about cardiac MR spectroscopy:
Hudsmith, L. E., Neubauer, S., JACC Cardiovasc. Imaging, 2(1), 87-96, (2009)



1D quantitative 31P spectroscopy from skeletal muscle of a rat. The highest peak at 0 ppm is PCr and the three small peaks at the right side are gamma-ATP, alpha-ATP and beta-ATP. (IEMR)



A 2D CSI image of a mouse heart. Three spectra from three voxels represent different regions in the FOV, including myocardium, mixed myocardium and blood, chest wall. (IEMR)

Body and Liver Fat imaging


It has been shown that not only body fat percentage, but also how the body fat is distributed is strongly related to cardiovascular disease. In addition, a large proportion of patients with nonalcoholic fatty liver disease have co-existing metabolic syndrome which is a major risk factor for cardiovascular disease. Therefore, we have applied whole-body fat and liver fat measurement on studying animals to assess the co-factor of cardiac heart disease.



Whole body fat images of an obese mouse
(IEMR)





Neuroimaging


Our lab is equipped with an RF coil setup specifically for rodent neuroimaging, producing e.g. T2-weighted images showing anatomical details with high resolution, or Gd enhanced T1-weighted images delineating glioma in a mouse brain. The mouse model of Medial Temporal Lobe Epilepsy (MTLE, kainate) is a well-established model for epilepsy research. We have applied T2-weighted and diffusion imaging, as well as manganese-enhanced T1-weighted images to detect the neuro-anatomical changes that occur during epileptogenesis.

Ex-vivo Imaging


We acquire high-resolution 3D ex vivo images overnight, making full use of the available machine time. The samples are fixated in Gd-doped agarose to give a bright background. The samples can range from animal organs, such as the heart, to human specimens.


Related publication from the core facility:
Krohn-Hansen, D. et al., J. Plast. Surg. Hand Surg., 49(5), 284-288, (2015)




High resolution image of a human eye, resolution is 52 Ám * 52Ám * 52Ám (IEMR)




High resolution image of an ex-vivo heart, resolution is 12.5 Ám * 12.5Ám * 12.5Ám (IEMR)



METHODS:

ONGOING RESEARCH:

Click for more information about Oslo Preclinical MR Core Facility and contact addresses.

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