Application on Signal Processing In MRI

Magnetic Resonance imaging(MRI) is a radiology technique that create pictures of the internal organs, tissue, and physiological processes occurring inside a patient's body. MRIs can provide an exceptional level of detail. MRI is different from the x-rays and computed tomography(CT) because it uses strong magnets and radio waves to produce the images, rather than the using ionizing radiation(x-rays). Because it does not use ionizing radiation, MRI is safer than x-rays and CT. An MRI scanner is essentially a giant magnet surrounded by a powerful magnetic field. 

 Now talking about safety, Your protection is the primary concern of the healthcare professional, so your radiology team will follow strict guidelines to keep you safe. Next this team will ask you to remove all your jewelry and metallic objects from your body as MRI room contain a heavy metallic energy. Your radiology team will also provide you with earplugs. MRI machines can be rather loud, so your radiology team will ask you to wear earplugs that protect your hearing.

 

 Now let's talk  about the Signal processing in MRIs. Application of Signal Processing in MRI are as follow's:

1. MR Fluoroscopy.
2. Real-Time Navigator Echoes.
3.  Real-Time Image-Triggered MR Angiography.
4. Interactive fast-Spin-Imaging.

 

MR Fluoroscopy

 

This term refers to continuous real-time MR imaging as might be used to facilitate to setup of high quality, diagnostic images. It is same to the use of x-ray fluoroscopy which serves a similar purpose in x-ray based imaging. In some sense this is the most direct application of real-time signal processing in that image reconstruction is performed as the data are acquired, and the operator controls the plane of section based on the sequence of displayed images. In an early demonstration with gradient echo acquisition the real-time capability was shown to reduce by almost an order of magnitude the time required to localize specific sections of the left ventricle Using spiral trajectories, imaging rates as high as 10 Hz have been achieved, and this has been used for cardiac imaging in patients who have been poor candidates for echocardiography.

 

Real-Time Navigator Echoes

The term “navigator” echo refers to an MR signal measured to monitor the motion of an object during the course of the acquisition of the image data. It was originally designed to allow for the data to be retrospectively corrected for the motion measured. With real-time processing techniques, however, it is possible to use the navigator echo to adjust the acquisition instantaneously, within millisec of acquisition. This can be useful for imaging of the heart, in which case it is necessary to account for both cardiac and respiratory motion. By restricting the data acquisition to the diastolic phase of the cardiac cycle, cardiac motion can be accounted for. By using a navigator echo to monitor the superior-inferior position of the diaphragm, this motion information can be used to include or reacquire the accompanying raw data or even to adjust the plane of excitation in an attempt in an attempt to track the heart position. More recently navigator echoes are being acquired along specific circular trajectories in k-space, so-called orbital navigator echoes, in order to have a high degree of sensitivity to rotation. These are being used in functional neuro MRI, a field which is particularly prone to error if the subject moves during the data acquisition.

Real- Time Image-Triggered MR Angiography 

 

 A growing application in MRI is the imaging of blood vessels using an intravenously administered contrast agent. Because of the wide range of transit times from patient to patient of the contrast bolus as it moves from the venous injection site to the arteries of interest, and because of the need to accurately time the MR acquisition to the arterial phase of the contrast bolus, it is necessary to determine proper timing on a patient-specific basis. One effective way to do this is real-time image or "fluoroscopically triggered"  contrast-enhanced MR angiography. With this technique good spatial resolution 2D images are acquired of the targeted arterial anatomy in real time at rates of 1-2 Hz after the contrast material has been injected. Upon visualization of contrast arrival in the targeted vessels, the operator triggers the very high resolution 3D scan by mouse click. This technique has proven to be highly reliable in capturing the desired arterial phase for blood vessels from the neck to the pelvis [24]. Real-time signal processing methods used are high speed reconstruction, interactive localization, and instantaneous switching between 2D and 3D pulse sequences.

Interactive Fast-Spin-Echo Imaging 

 

Yet another emerging application of real-time MRI techniques is the use of RARE [4] or fast-spin-echo imaging on an interactive basis. When implemented as a single shot approach all of the desired k-space data are read out in one excitation cycle. Recently this method has been incorporated with real-time reconstruction and parameter control to allow interactive imaging. As part of this, the technique of driven equilibrium has been used to maintain high SNR, even for TR times of 2000 millisec or less, and Wiener demodulation has been incorporated to restore spatial resolution loss due to T2 modulation. The resultant interactive spin-echo method is currently being used in studies of the pelvic floor, for fetal imaging, and improved methods for MR cholangiopancreatography (MRCP).

In End I would like to say that the Real-Time MRI signal processing techniques are growing in importance in allowing expanded applications of MRI as well as improved reliability by allowance for patient specific characteristics.