MRI Essay Example | Topics and Well Written Essays - 1500 words - 1

MRI - Essay Example Due to huge abundance of water in the body, hydrogen atoms are focused upon in this process. Upon applying the magnetic field, the hydrogen atoms align in the direction of the magnetic field. Next, when radio waves are added to the magnetic field, it results in the deflection of the magnetic field and resonation of the hydrogen atoms. Resonation frequency of hydrogen atoms is dependent upon the strength of the magnetic field. Upon the switching off of the radio frequency, the atoms get aligned again, generating a signal which is used to create MRI image. After giving subtle time for atoms to relax, multiple signals are produced to detect abnormalities in the tissues. (Berger, 2002) These signals are generated in the form of an image depicting significant information. (Dawson, 2008) (Blink, 2004) It has wide range of applications in evaluating blood flow in the arteries (Clinical Policy, 2001) and diagnosis of soft tissue problems such as brain tumours, multiple sclerosis, torn ligame nts, shoulder injuries and earlier stages of stroke. MRI offers multiple privileges to probe deep into soft tissues which CT scans or X-ray do not provide. Secondly, they don’t use any ionising radiations and are thus claimed safe as radio waves are found all around and do not damage the tissues. (Berger, 2002) Thirdly, MRI offers diagnosis of a specific area in the patient at various planes unlike CT scan that is limited only to one plane. (WebMD, 2009) However, there are several limitations to it such as 1) high cost of an MRI scan; 2) victims of claustrophobia are hesitant to undergo the diagnosis and condition to hold breath for long durations, 90 minutes or so, is quite uncomfortable for aged patients. (Michaelmas, 2004) Nevertheless, MRI is one of the major breakthroughs in medicine, allowing the doctors and researchers to accurately diagnose disease conditions of ailing humans. Magnetic Resonance Venography (MRV) is another technique based on nuclear magnetic resonance that is used particularly for monitoring the blood flow in veins of the body. (Vega, 2008) A detailed account of the different scenarios at which MRA and MRV are being used is discussed in a report by Clinical policy Bulletins. (Clinical Policy, 2001) The only difference between MRI and MRV is that MRV uses special computer software to generate the images. This paper will discuss the various techniques used in MRV namely Phase Contrast 3D PC MRV, Time of Flight 3D TOF MRV and Contrast enhanced (3D MRV CE) and MRI scanners in general. Phase Contrast 3D PC MRV This technique makes use of velocity induced shifts to measure blood flow. The velocity of blood flow is proportional to the phase shift, thus giving true quantification of blood flow and direction of blood flow. (Lirng, 2010) (Srichai MB, 2009) Signal intensity is encoded by velocity on the MR image, where stationary protons appear in gray colour. Blood flow in one direction is brighter as compared to the flow in the opposite direction. (Srichai MB, 2009) A significant factor called VENC factor, which is targeted to visualize arteries or veins in the region of interest. The higher the VENC factor, the arteries become more clear and vivid on the MRI image; lower VENC factor values help in visualizing veins. The direction of flow and flow velocities can be calculated using the MRI images. (Medical Physicist, n.d.) Various implications of 3D-PC have been explored in the past decade. Stoquart-ElSankari et al investigated