This is achieved by increasing using multiple turns of the coil to increase its sensitivity, to allow high duty of pulsing. At the same time, the design will consider the inductance of the coil gradient, which will have to be minimized. The components of the MR system that are important in this regard include the gradient amplifier, voltage across the inductive, and the resistance across the gradient coil. Q3. The effects of gradient G(r) on Larmor processional frequency at a position r is to change the processional frequency at this position r. Q4. The optimal separation of two current carrying loops to produce as linear a magnetic field gradient as is possible at the centre of the two loops is when 2Z1 =, where a refers to the coil radius. The reason as to why this separation is different from the necessary one to produce a homogenous field is because separating the field in that manner help in generating relatively pure fields. Q5. Slew rate refers to the maximum gradient strength as a factor of the rise time (Vmax/L). The slew rate needs to be as large as possible because it helps in stimulating the peripheral nerves of the human body, thereby creating a “crawling” type sensation on the skin. Q6. Reason why it is necessary to shield gradient coils: This is done mainly to reduce the net inductance of the system Q7. Type of effect caused by gradient coil shielding to reduce combat the effects of eddy-current induced magnetic fields. Q8. The causes of undesirable sounds produced by magnetic resonance imaging at runtime are due to gradient coil experiencing magnetic forces and torques when being pulsed. The reason is that as the coils get physically restrained, the energy associated with the magnetic forces is released acoustically as loused sound. The undesirable sound can be reduced by: Designing a gradient coil that are torque and force balanced; Shaping the gradient pulses to reduce sound produced; Using acoustically absorbent formers for the coils; Encasing the gradient coils in an evacuated chamber so that waves of the sound are not compatible. Q9. The main cause of nerve stimulation due to magnetic resonance imaging is the slew rate push and the maximum gradient strengths that induce field in the patient, thereby stimulating the nerves. This is mainly observed by experiencing a “crawling” type sensation on the skin. It can also be observed through twitching of muscles as the nerves get stimulated. Q10. The causes of impurities in the static magnetic field (BO) include: The patient and radiofrequency coils in the DSV, which may alter the magnetic field due to their magnetic properties; Imperfection in the magnetic manufacturing process; Installation site where ferrous installations done near the magnet may end up altering the homogeneity of the magnetic field over the DSV. Q11. The two types of image quality reduction caused by zonal impurities in the static magnetic field are: Artifacts; Homogeneity. Part B The three topics in my order of preference are: 1) Interventional MR system; 2) MR gradient coils: action and performance; 3) RF resonators for MR applications. The main reason as to why I have chosen the three topics is due to my desire to learn more about them so that I can acquire more knowledge
Part (A) Q1. Desirable properties of a pulsed gradient coil system The following are the desirable properties of a pulsed gradient coil system: The gradient must be very linear over DSV with impurities not more than 5%; The gradient coil set must be of low resistance to minimize power dissipation; Should be able to be pulsed very first; Should be shielded to prevent induction of eddy currents to the magnetic structure when gradient is pulsed; Forces, torques and acoustic output as well as vibration need to be minimal…
Functional magnetic resonance imaging or fMRI is a process of mapping brain activities by analysing the modifications in blood flow and oxygenation levels that vary according to neural activities taking place within the brain (Huettel, Song and McCarthy, 2009).
Figure 1 shows an example of an MRI image from a moving patient. In such cases, use of sedation or general anesthesia is warranted to increase tolerance to an unpleasant but necessary procedure, and to expedite MRI imaging of a distressed patient (Medical Advisory Secretariat, 2003; Shellock, 2011).
Magnetic resonance Imaging involves the use of powerful magnetic fields and radio frequencies to produce computerized and detailed images of soft tissues, organs and bones, as well as any other internal body structure. Unlike some imaging techniques, such as X-ray or computed tomography, MRI does not require the use of ionizing radiation.
735–737). This has particularly been witnessed in creasing of breast as a way of treating cancer and other related malignant tumors. However, technicians and radiologists working on these systems quite often encounter image artifacts related to radio waves with strong magnets in the scanner.
As one of the major types of radio frequency (RF) coils, phased array coils offer several distinct advances to MRI technologies. Those include increased signal to noise (SNR) ratios for improved image quality; the ability to do parallel imaging faster and/or with improved image quality; and reduced scan times in general.
The discussion includes the three fundamental magnetic types that comprise an MRI machine, and the conditions for which their functioning is optimized. Theoretical prototypes are also discussed, as well as different configurations to increase the performance of radiofrequency resignation pursuant to a high quality scan.
This technique - which primarily which exploits the magnetic properties of certain nuclei - is based on nuclear magnetic resonance, a phenomenon first measured by Isidor Rabi in molecular beams, and then described fully by Bloch and Purcell who theorized and expanded the technique to both liquids and solids.
Q8. The causes of undesirable sounds produced by magnetic resonance imaging at runtime are due to gradient coil experiencing magnetic forces and torques when being pulsed. The reason is that as the coils get physically
NR) ratios for improved image quality; the ability to do parallel imaging faster and/or with improved image quality; and reduced scan times in general. However, phased array coils have their own disadvantages. Those include higher component costs and more noise and artifacts for
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