Imaging



MR Fingerprinting may offer much improved method of quantitative tissue analysis

 



At the 24th Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM) in Singapore, in May this year, Case Western Reserve University and Siemens Healthcare announced an exclusive research partnership to further develop a quantitative imaging method known as Magnetic Resonance Fingerprinting (MRF). Researchers at the Cleveland, Ohio, university and Siemens’ developers will further refine this highly promising method of quantitative tissue analysis.

“The most innovative applications can only be brought to life through the collaborative efforts of industry and research,” said Dr Christoph Zindel, head of the business line Magnetic Resonance at Siemens Healthcare.

Mark Griswold, PhD, professor of radiology at Case Western Reserve, explained: “The goal of MR Fingerprinting is to specifically identify and characterize individual tissues and diseases. But to try to get there, we’ve had to rethink a lot of what we do in MRI.”

MRF is an innovative, highly versatile and insightful method of measurement, intended to provide non-invasive, userand scanner-independent quantification of tissue properties. The MRF method is designed to measure a wide range of parameters simultaneously, quantifying many important tissue properties.

Presently, the evaluation of MR images is generally qualitative. In doing so, the properties of the pathology are determined by observing differences in contrast between tissues, instead of being based on absolute measurements of individual tissue properties. Quantitative approaches exist, involving the measurement of diffusion, fat/iron deposits, perfusion or relaxation times, for example. But these sequences often require significant amounts of scan time, and the results vary depending on the scanner and the user. Given the potential low level of variance across a large number of examinations and its expected reproducibility across scanners and in different institutions, MRF could achieve more accurate monitoring and evaluation of patient treatment.

The MRF technique does not acquire traditional clinical images, but instead is designed to gather tissue information based on the signal evolution from each voxel. Acquisition parameters are varied in a pseudorandom fashion, while the signal evolutions are recorded. These are then compared to a database, or “dictionary”, to find the entry that best represents the acquired signal evolution of each voxel.

The signal evolutions equate in many ways to “fingerprints” of tissue properties, which, like the identification of human fingerprints in forensics, can only be analyzed by comparing them with a file containing all known fingerprints. The dictionary is equivalent to the database where all the known fingerprints are stored, together with all the information relative to each person. In the forensic case, each fingerprint points to the feature identification of the associated person such as name, height, weight, eye colour, date of birth, etc. In the case of MRF, each fingerprint in the dictionary points to the MR related identification features of the associated tissue (such as T1, T2, relative spin density, B0, diffusion, etc.).

The CWRU research team is driving the expansion of this method for a range of different tissue properties. At the same time, the university is working toward expanding the technology to cover additional fields of application. The research team has successfully performed initial tests with brain and prostate tumour patients as well as breast cancer patients with liver metastases. MRF has also been used in cardiac examinations and with patients with multiple sclerosis. For Siemens, the focus of this collaboration is to improve reproducibility and possibly to extend the procedure to different MR scanners and fi eld strengths. Case Western Reserve uses numerous systems from Siemens, and employs the Magnetom Skyra 3-tesla system for the purposes of this research project.

An initial result of this collaborative process launched in September 2015 is a “Work-in-Progress” package, an imaging package for selected Siemens scanners used in research. These WIP packages have been successfully tested since January 2016 at the University Hospital Essen, Germany, and the Medical University of Vienna, Austria, using further Siemens MRI systems.

“The MR Fingerprint technique lets us see more details than the standard imaging process, and has the potential to redefi ne MRI,” said Professor. Siegfried Trattnig, of the Center of Excellence for High Field Magnetic Resonance at the Medical University of Vienna, referring to the initial research studies involving patients with malignant brain tumours and low-grade gliomas.

“In this way, MRF could help us, as radiologists, to make the paradigm shift from qualitative to quantitative imaging and to incorporate quantitative data into our daily routine.”

This has the potential to reduce scan times and in turn, bring considerable cost savings in the future.


‘Salt’ MRI scans could give a clearer picture of disease

 
MRI experts at The University of Nottingham have won a £1 million grant to adapt scanning techniques to pick up sodium in the body. The research could lead to much more detailed MRI scans in the future with signifi cant improvements to the diagnosis and treatment of many diseases.

A novel technique to use the body’s natural sodium (salt) content to provide a more detailed picture of tissue health and disease is to be pioneered by MRI experts at The University of Nottingham.

The team at the Sir Peter Mansfi eld Imaging Centre (SPMIC) will develop the untapped potential of Sodium MRI as an advanced scanning technology.

Current clinical MRI uses hydrogen in the body’s water and fat to produce scans, but this does not provide all the information about tissue health and disease progression stages. Sodium ions naturally occurring in the body are much smaller than water molecules and are involved in many body functions associated with pathology. Sodium MRI has great potential to be a useful new high and ultra-high fi eld scanning target in the future.

Kidney disease will be the main application of the research working in collaboration with the Centre for Kidney Research and Innovation (CKRI), but the team believes that Sodium MRI can also be used for more accurate diagnosis and monitoring of other diseases, and perhaps will give new insights into disease mechanisms as sodium management is important in the brain, lung, liver, and musculoskeletal system.

The grant will allow the researchers to develop sodium MRI on the 3T and 7T magnetic field scanners at the SPMIC, University Park Campus, Nottingham. The team will use MRI coils for sodium imaging – these are the receivers of radiofrequency signals in the MRI scanner specifi cally tuned to the resonant frequency of sodium ions. The researchers will develop new pulse sequences so these new coils can image the torso and limbs. The team hopes eventually to take Sodium MRI technology from bespoke research into real world healthcare in healthy volunteers and patients.

Translational imaging researcher Dr Galina Pavlovskaya, School of Medicine, SPMIC said: “Sodium MRI is a novel and undeveloped technology which has huge potential for the healthcare of the future. We are delighted to receive the funding to take it forward at Nottingham. The technique of using sodium ions in the body as a biomarker for imaging is very challenging because of the lower detectability of the sodium signal in biological tissue by currently available MRI scanners. However, high and ultra-high magnetic fi eld scanners available in the Centre should be able to help to circumvent this obstacle.

“Sodium ions are much smaller than the hydrogen protons bound to oxygen molecules in the water in our bodies which are mapped by conventional MRI. Therefore, sodium has the capacity to give us a much clearer and detailed picture of the structure and health of an organ from deep inside the tissue. Our aim is to refi ne the technology so we can turn theory into clinical reality.”

Co-researcher Dr Susan Francis, School of Physics, SPMIC added: “The team has a special interest in new types of functional MRI using novel targets like sodium as quantitative biomarkers of disease in the body, in particular in the kidney. The kidney is an ideal target for our project because it is important in the regulation of sodium in the body. If we can image how sodium is distributed in the kidney and how that differs in a diseased kidney, the impact on the diagnosis and treatment of kidney injury or disease is potentially great. The technique also has specifi c relevance to understanding sodium and water balance in dialysis patients.

The project will end in 2018 with a Sodium MRI Conference for the worldwide MRI research and clinical community.


‘Researchers make breakthrough in new MRI scan technology for lung disease

 
New scanning technology which will give a much clearer picture of lung disease has taken a major step forward thanks to scientists at The University of Nottingham.

The experts at the Sir Peter Mansfi eld Imaging Centre have developed a process using specially treated krypton gas as an inhalable contrast agent to make the spaces inside the lungs show up on a Magnetic resonance imaging (MRI) scan. It’s hoped the new process will eventually allow doctors to virtually see inside the lungs of patients.

Traditional magnetic resonance imaging uses hydrogen protons in the body as molecular targets to give a picture of tissue but this does not give a detailed picture of the lungs because they are full of air. Recent technological developments have led to a novel imaging methodology called Inhaled Hyperpolarised Gas MRI that uses lasers to ‘hyperpolarise’ a noble (inert) gas which aligns (polarises) the nuclei of the gas so it shows up on an MRI scan.

The work will make 3D imaging using ‘atomic spies’ like helium, xenon, or krypton possible in a single breath hold by the patient. Nottingham has pioneered hyperpolarized krypton MRI and is currently ad-vancing this technology towards the clinical approval processes.

Hyperpolarised MRI research has been trying to overcome a problem with these noble gases retaining their hyperpolarised state for long enough for the gas to be inhaled, held in the lungs and scanned. Now in a paper published in the Proceedings of the National Academy of Sciences, the Nottingham team has developed a new technique to generate hyperpolarised krypton gas at high purity, a step that will signifi - cantly facilitate the use of this new contrast agent for pulmonary MRI.

Chair in Translational Imaging at the Sir Peter Mansfi eld Imaging Centre, Professor Thomas Meersmann, said: “It is particularly demanding to retain the hyperpolarized state of krypton during preparation of this contrast agent. We have solved a problem by using a process that is usually associated with clean energy related sciences. It’s called catalytic hydrogen combustion. To hyperpolarise the krypton-83 gas we diluted it in molecular hydrogen gas for the laser pumping process. After successful laser treatment the hydrogen gas is mixed with molecular oxygen and literallypresexploded it away in a safe and controlled fashion through a catalysed combustion reaction.

"Remarkably, the hyperpolarized state of krypton-83 esurvivesf the combustion event. Water vapour, the sole product of the ecleanf hydrogen reaction, is easily removed through condensation, leaving behind the purifi ed laser-polarized krypton-83 gas diluted only by small remaining quantities of harmless water vapour. This development signifi cantly improves the potential usefulness of laser-pumped krypton-83 as MRI contrast agent for clinical applications.

"This new technique can also be used to hyperpolarise another useful noble gas, xenon- 129, and may lead to a cheaper and easier production of this contrast agent.

As part of a recent Medical Research Council funding award, hyperpolarised krypton-83 is currently being developed for whole body MRI at high magnetic fi eld strength in the Sir Peter Mansfi eld Imaging Centrefs large 7 Tesla scanner. Studies will be carried out fi rst on healthy volunteers before progressing to patient trials at a later phase. 

  • doi:10.1073/pnas.1600379113

MRI helps predic preterm birth

 
MRI of the cervix is more accurate than ultrasound at predicting if some women will have a preterm birth, according to a new study from Italy appearing in Radiology.

Early dilation of the cervix, a neck of tissue connecting the uterus with the vagina, during pregnancy can lead to premature delivery. Women in their second trimester of pregnancy with a cervix measuring 15 millimetres or less, as seen on ultrasound, are considered to be at higher risk of preterm birth. However, ultrasound has limitations as a predictor of preterm birth, as it does not provide important information on changes in cervical tissue in the antepartum phase just before childbirth.

“A better understanding of the process of antepartum cervical remodelling, loosely divided in two distinct phases called softening and ripening, is critical to improve the diagnosis of cervical malfunction and anticipate the occurrence of birth,” said thestudy’s lead author, Gabriele Masselli, MD, from the Radiology Department at Sapienza University in Rome.

To learn more, D. Masselli and colleagues used an MRI technique called diffusionweighted imaging (DWI) to examine pregnant women who had been referred for suspected foetal or placental abnormality. DWI reveals differences in the mobility of water molecules in tissue and the results can be used to create apparent diffusion coeffi cient (ADC) maps that provide a measure of local cell density. DWI has been increasingly used for abdominal and pelvic diseases, but has not been tested for the evaluation of the uterine cervix in pregnant patients.

Each of the 30 pregnant women in the study had a sonographically short cervix and a positive foetal fi bronectin test between 23 and 28 weeks of gestation. Foetal fi bronectin is a glue-like protein that helps hold the foetal sac to the uterine lining, and the presence of it before week 35 of gestation may indicate a higher risk of preterm birth.

Of the 30 women, eight, or 27%, delivered within a week of the MRI examination. The other 22 delivered an average of 55 days later. The researchers compared differences in ADC values at MRI between two areas of the cervix: the inner, subglandular zone and the outer, stromal area. While stromal ADC and sonographic cervical length showed no difference between both groups, the subglandular ADC was higher in patients with impending delivery, suggesting an increased mobility of water molecules in that area consistent with cervical ripening.

“Our results indicate that a high ADC value recorded at the level of the subglandular area of the cervix is associated with the imminent delivery of asymptomatic patients with a short cervix,” Dr Masselli said.

 

 Date of upload: 8th July 2016

 

                                  
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