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Enhancing susceptibility weighted imaging through collaborative research

Clinical News
Yoneda, Tetsuta Kumamoto University • Japan

At Philips we listen to our customers and continuously collaborate with our clinical partners on developing, testing and evaluating new methods. The insights and contributions of our customers feed into the development of new or improved features.

 

When Tetsuya Yoneda, PhD, physicist at Kumamoto University Hospital in Japan, had discussed his ideas on susceptibility weighted imaging with the Philips Japan clinical science team, it was the start of a fruitful collaboration. The results helped the Philips product development team.

 

Susceptibility weighted imaging is an MR imaging technique used to visualize susceptibility differences between tissues. Magnetic susceptibility represents the ability of a tissue to become magnetized in a magnetic field. Tissues and substances behave differently in a magnetic field, because they have different paramagnetic and diamagnetic properties that influence T2* and phase.

 

“The aim in susceptibility weighted imaging is to enhance contrast between materials with different susceptibility to visualize, for instance, deoxygenated blood as a result of the exposed iron it contains. Deoxygenated blood also appears dark on T2*-weighted images, but the sensitivity is higher on susceptibility weighted imaging,” says Dr. Yoneda.

 

“Susceptibility weighted imaging also uses phase information, which depends on field strength, so the effect is stronger on a 3.0T system,” says Dr. Yoneda. “That is why we worked with the Achieva 3.0T TX system. We mainly use the 32-channel head coil as it provides very nice quality imaging.”

 

 Tetsuya Yoneda, PhD Kumamoto University Hospital
Tetsuya Yoneda, PhD
Kumamoto University Hospital

Redesigning data reconstruction

“I have worked on the reconstruction algorithm of susceptibility weighted imaging data. The initial susceptibility weighted imaging methods were based on differences in paramagnetic properties, which is sufficient to visualize hemorrhage that contains deoxygenated blood. Additionally, I explored the possibility to make the method sensitive to diamagnetic materials, which could also allow visualization of accumulations containing diamagnetic materials, such as calcifications.”

 

Visualizing fine anatomical structures.  These images illustrate the power of the reconstruction with phase difference enhanced imaging (PADRE) to delineate fine anatomical structures. The left and middle images show many brainstem tracts with good contrast. These are very difficult to visualize on conventional MRI sequences. In the right image, neuronal nuclei in the thalamus are easily seen. The capability to delineate neuronal nuclei and tracts – with realistic scan duration, high spatial resolution, high contrast – may be a useful tool for investigating multiple system atrophy as in Parkinson’s disease and surgical procedures such as deep brain stimulation. Achieva 3.0T TX, 3D-T1FFE, 0.5 x 0.5 x 2.0 mm (1.0 mm overcontiguous), TE 23 ms, TR 32 ms, scan time 3:40 min. Images courtesy of Dr. Kitajima, MD, Kumamoto University

Balancing scan parameters

In collaboration with technologists, neuroradiologists, medical doctors and the Philips Japan MR team Dr. Yoneda finally achieved the desired results. “The mathematical function is now completely different. It enhances any kind of phase information and not just paramagnetic phase information like in the initial methods on our system,” says Dr. Yoneda. “Another difference is that the method eliminates the phase-wrapping artifact from the phase information. That phase wrap arises from long TE, but a long TE is desirable to generate high contrast on the phase information, so we had to find a compromise to get the good contrast.”

 

“High sensitivity for venous blood products makes it possible to see hemorrhage and even microbleeds,” says Dr. Yoneda. “Using my method we have also imaged patients with neuro and brain diseases such as arteriovenous malformation, cortical displacement, degenerative diseases such as Parkinson’s disease, multiple sclerosis and multiple system atrophy. We are hoping to extend our work to the rest of the body.”

 

The collaboration between Dr. Yoneda and Philips is ongoing and focusing on further exploring together the potential of this technique.

 

Susceptibility weighted imaging methods

Click an image to enlarge
 Susceptibility weighted image Susceptibility weighted image reconstructed with phase difference enhanced imaging SWIp image
Susceptibility weighted image
Susceptibility weighted image reconstructed with phase difference enhanced imaging
SWIp image
 Susceptibility weighted image zoomed image <br>
phase difference enhanced SWIp image
Susceptibility weighted image
zoomed image
phase difference enhanced
SWIp image

 

On the susceptibility weighted images many vessels are seen. The SWIp images show also small vessels, and with higher contrast. For instance, the deep medullary veins (blue arrows) are better delineated on the SWIp image. This high contrast delineation of vessels is realized with the multi-echo acquisition, where the short TE magnitude image is used to create a high-signal background with low-signal susceptibility artifact; the long TE phase image information is used to create high vessel contrast; and scan time is kept short.

     

The susceptibility weighted images reconstructed with phase difference enhanced imaging (PADRE) show calcification in the pineal body (red arrow). The zoomed image shows white matter tracts such as the optic radiation (blue arrow) which reaches the occipital lobe (orange arrow).

 

The susceptibility weighted images are acquired by Dr. Yoneda using Achieva 3.0T TX, 3D-T1FFE, 0.45 x 0.45 x 2.0 mm (1.0 mm overcontiguous), TE 20 ms, TR 23 ms.

   

The SWIp images are acquired by Philips using Ingenia 3.0T, 0.4 x 0.6 x 1.0 mm (0.5 mm overcontiguous), TE 7.2, 14.7, 22.2, 29.7 ms, TR 38 ms, SENSE 3.5, 4:08 min.

Different contrast types

 2D MS coronal PRESTO, long TE
2D MS coronal
PRESTO, long TE

 

MRI has the ability to use different scan methods to create different contrast types, which is an advantage over other modalities. Usually only the magnitude images are used, but phase difference enhanced imaging reconstruction could be applied to different sequences. In this way, different sequences can naturally make different background contrast, resulting in various types of SWIp-like contrast. We are currently studying the use of PADRE in different sequences to explore whether this could provide useful additions in clinical scanning. Achieva 3.0T TX.

 

Tetsuya Yoneda, PhD, is physicist at the Department of Medical Physics in Advanced Biomedical Sciences, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan.

 



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Clinical News
Achieva 3.0T TX
Brain, hemorrhage, Neuro, Parkinson's, susceptibility weighted imaging, SWIp
 

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