MRI (Practice Exam Qs) Question And Answers Well Detailed 100% Explained Answers.

T1, T2 and PD weighted images are obtained by controlling the parameters referred to as "Time to Repeat" (TR) and "Time to Echo" (TE). Discuss the consequences (positive or negative) of choosing a long TE in terms of image quality - correct answer Having a long TE does provide good contrast in a T2 image but the signals have reduced too, therefore the SNR has reduced (noisy image) Increased TE also increases the acquisition time and chances of patient motion Long TR and Long TE - correct answer T2 weighted image Short TR and Short TE - correct answer T1 weighted image Long TR and Short TE - correct answer PD weighted image Short TR and Long TE - correct answer Mixture of T1 & T2 It is important to have a uniform gradient magnetic field along the entire length of the patient. Discuss the purpose of this gradient field, why uniformity is so important and what is used to ensure that this is the case - correct answer We need to know what the magnetic field is at each point of the body so that we can send in the correct RF signals to obtain resonance with the dipoles in the required slice. If the magnetic field is not uniform then there will be a mismatch with the RF and the wobble frequency of the appropriate dipoles. Shim coils make sure that the magnetic field is uniform before applying the slice gradient field You receive a patient for post-operative assessment after spinal fixation. Describe the process to ensure a patient is safe to enter the MRI room - correct answer Safety questionnaire - any other devices e.g. pacemaker Check implant against safety info on MRIS and/or manufacturers website i.e. MRI safe, unsafe or conditional Date of surgery, how long has fixation been in (6-8 weeks usually considered safe - decided locally) Changed into gown - all loose metal removed, belts, hair pins etc The patient is concerned they might feel claustrophobic. Explain 4 ways you will help ensure they are comfortable as possible during the examination - correct answer There is a microphone so you will be able to talk with them between sequences There is a buzzer so if they are anxious they can squeeze it and you will check on them and bring them out of the scanner if they wish Through the headphones you can play relaxing music The coil may have a mirror or you can offer them prism glasses which help you see out of the scanner There is a fan blowing cool air over the patient Explain the difference between Spin Echo (SE) and Gradient Echo (GE) signal generation. Diagram acceptable - correct answer SE only uses RF pulses to generate signal. A 90degree RF excitation pulse flips the magnetisation into Mxy, then a 180degree refocusing pulse is applied and signal is generated GE uses an excitation pulse of less than 90degree RF followed by gradient pulses (as opposed to 180degree RF pulses) to refocus spins MR Techs have to align scans to anatomy for accurate slice acquisition. Describe in words the correct slice position for the axial plane of the brain - correct answer The axial plane for MRI is found by a line bisecting the anterior and posterior commissures of the corpus callosum (some sources say 5degrees caudal from this line) Demonstrate your understanding of the significance of FLAIR imaging, when detecting Multiple Sclerosis plaques - correct answer FLAIR saturates out signal from cerebrospinal fluid which is important as MS plaques appear bright on T2 weighted images. MS plaques often originate in the corpus callosum, which neighbours the lateral ventricle which contains CSF, therefore if we saturate out signal from CSF the plaques will be more obvious You are imaging a glioma and the Radiology Registrar has injected gadolinium. What image weighting will the subsequent sequences be acquired with? Justify your answer - correct answer T1 weighting as gadolinium reduces T1 time of tissues where it collects such as tumours Define NSF and explain who is at risk of this reaction - correct answer Nephrogenic systemic fibrosis This reaction occurs in patients who have poor renal function Analyse the following statement, demonstrating your understanding of pulse sequence selection and the basic physical principles behind image artifacts: "T2* GE is the optimal pulse sequence for T2 imaging of the cervical spi