ARMRIT Review Test Questions With Correct Answers

The exact middle of the bore of the magnet is termed: - Answer Isocenter Without proper safety limits on the MR system exposure to the time-varying magnetic fields created by the rapid switching of the gradient could create a potential environment for: - Answer Including electrical current in the patient's tissues Faraday's Law deals with induction of a current by a magnet. true or false? - Answer true The orientation of the main magnetic field of a low field permanent magnet is vertical. True or false? - Answer True ; permanent lowfield magnets utilize a magnetic field oriented vertically Superconductive magnets have high homogeneity compared to other magnets types. true or false? - Answer true ; One advantage of a superconductive magnet is its excellent homogeneity The start up cost for a superconductive magnet is high. true or false? - Answer true ; Initial cost may exceed two million dollars in addition to the expensive cyrogen up keep. A type of magnet that is generally used for a 1.0t or a 1.5t system is a: - Answer Superconductive magnet The basic type of magnets used in MR are: - Answer Permanent, resistive , superconductive A procedure called shimming: - Answer Adjust the magnetic field to achieve the most homogenous field Superconductive magnets utilize two types of cyrogens. - Answer Helium and nitrogen Types of transmit coils are: - Answer a) Body, b) head, c) volume coils, d) all of the above. D all of the above Various types of receiver coils are: - Answer a) solenoidal coil, b) volume,birdcage,surface coil, c) Helmholtz pair coil, d) All of the above: D all of the coils are true receiver coils To gain SNR and gain high resolution: - Answer Use a small surface coil Which of the following is not an example of a surface coil: - Answer body coils are not surface coils In a cross-sectional view of the magnet bore, which set of coils are the closest to the bore? - Answer RF coil- the cross sectional of the MR system reveals the order of thecoils: the magnet bore, then the RF coils, Then the gradient coils, then the shim coils & the outer most are magnet coils. MR systems can be shielded by two processes. They are: - Answer Passive and active shielding The more expensive type of shielding that uses additional solenoid magnets outside the cyrogen bath that restricts the magnetic field line to an acceptable location is the: - Answer Active- passive shielding can be accomplished by lining the walls with steel while the more expensive alternative is active shielding Surface coils are connected inside the scanner by cables. These cables shouldnt touch the patient because: - Answer They could burn the patient. Quadrature design coils give you a lower SNR. true or false? - Answer True: Quadrature coil designs improve SNR due to increased coverage. The two coils in a magnet used to transmit RF are the shim and tune coils. true or false? - Answer False: transmit coils are usually the body and head coils. Magnetic field gradients are generated by what? - Answer coils of wire situated within the bore of the magnet. In the event of a cryogenic leak or catastrophic magnet quench, the first thing the technologist should do is? - Answer evacuate all persons from the scan room. The given field strength (ex..1.5T) of the magnet is maintained at the: - Answer Middle od the axis of the bore, middle of the axis reamins at the field strength. When employing a surface coil the signal intensity: - Answer decreases as anatomy gets further from the coil. Surface coils are "receive only" coils. true or false? - Answer False The largest possible receiver coil should be chosen: true or false? - Answer False- optimally smallest coils are best Surface coils are free standing & have no electrical components. true or false? - Answer false The precessonial frequency of hydrogen at 1.5T is 68MHz. true or false? - Answer False- Hydrogen @1.5T is 63.86MHz What happens to the precessional frequency of those protons which experience a higher magnetic field? - Answer It increases To achieve the shortest scan time possible, which of the following would not be selected. - Answer Shortest TE possible. TE doesnt effect scan time In a 2DFT scan using a TR of 1 second, a TE of 30msec, a FOV 24, Matrix 128 & 2 NSA. What is your total scan time for 1 slice? - Answer 4.2 minutes; 1x128x2/60=4.2 In MR , the frequency of water is_________ as compared to the frequency of fat. - Answer Higher- The frequency in H2O is higher than fat The following statement: Any signal must be sampled at least twice per cycle in order to represent or reproduce it accurately; is a mathematical principle called: - Answer Nyquist Theorem If the Nyquist theorem is not adhered to in the MR experiment what is the result? - Answer Aliasing At equilibrium more nuclear spines are________ with the magnetic field. - Answer In Alignment When the magnetic field is energized the nuclear spins start to return to process, as they return to equilibrium they give of: - Answer NMR signal Repeatedly applying RF pulses at time internals less than the T2 & T1 times of the tissues refers to: - Answer A steady state- a steady state is a condition where the TR is shorter than the T1 & T2 times of tissues. In an MRI expirement , what occurs first after RF excitation - Answer T2* Decay The most widely used pulse sequence is: - Answer Spin-Echo For the spin-echo pulse sequence, FID is the signal used to create the image. true or false? - Answer False- pulse sequence echoes are the MR signals that make an image in SE scans The signal produced immediately after a RF pulse is: - Answer FID - signal produced immediately after a RF pulse. Which of the following is not an intrinsic parameter effecting image contrast? - Answer Repetition time At 1.0T fat has a T1 relaxation time of approximately: - Answer 180msec At 1.0T the T2 relaxation time of water is approximately: - Answer 2500msec At 1.0T the T1 relaxation time of CSF is approximately: - Answer 2000msec At 1.0T the T2 relaxation time of white matter is approximately: - Answer 80msec The T1 time of fat is said to be: - Answer Short The molecular mobility in water (CSF) causes the T1 time of water (CSF) to be: - Answer Long- The NMV of water takes longer to realign & the T1 of water is long The T2 time of fat is said to be: - Answer Short The T2 time of water is said to be: - Answer Long The relative number of protons per unit volume defines: - Answer PD - Protons denisty refers to the relative # of protons per unit volume of tissues An example of tissue with a low proton density would be: - Answer Cortical Bone Which of the following statements is true: - Answer Fat has a Short T1 & a short T2 How does the signal from fat & water appear on T2-weighted images? - Answer Dark fat & bright water Which of the following statements is true of T1-weighting? - Answer TR controls the amount of T1-weighting. (because the TR controls how each vector can recover before it is excited by the next RF pulse to achieve T1-weighting the TR must be short) Which of the following statements is true of T2-weighting? - Answer TE controls the amount of T2-weighting; for T2-weighting the TE must be long on SE The contrast from PD, T1, T2, occur simultaneously & contribute to the image contrast; true or false? - Answer True For a T1-weighted image you would want to: - Answer exaggerate T1 & diminish T2 For a T2-weighted image you would want to: - Answer Exaggerate T2 & diminish T1 For a T1-weighted image you would use a: - Answer Short TR & Short TE For a T2-weighted image you would use a: - Answer Long TR & Long TE For a Proton Density image you would use a: - Answer Long TR & Short TE For a Proton density weighted image you would want to: - Answer diminish T2 and diminish T1 Which of the following set of parameters used for a spin echo pulse sequence would yield an image that would be T1-weighted. - Answer 500msec TR, 20msec TE Which of the following set of parameters used for a SE pulse sequence would yield an image that would be T2-weighted. - Answer 2500msec TR, 80msec TE Which of the following set of parameters used for a SE pulse sequence would yield an image that would be PD-weighted. - Answer 2000msec TR, 30msec TE In real life, the transverse magnetization decays much faster due to experiencing slightly different magnetic fields & is called: - Answer T2* In a SE pulse sequence what is used to re-establish phase Coherence caused by spatial inhomogenity of the magnetic field? - Answer A 180 degree RF pulse T2* is actually slower than T2. true or false? - Answer false- T2* is actually faster than T2 because it is a combination of Two effects How can dephasing caused by magnetic field inhomogenities be compensated for in MRI? - Answer Use a 180 degree RF pulse A SE sequence is compromised of: - Answer A 90 degree RF pulse followed at a specific time by a 180 degree pulse An inversion recovery pulse sequence is comprised of: - Answer A 180 degree RF pulse followed by a 90 degree RF pulse Fat has a short T1 & a short T2. true or false? - Answer true What timing parameters are selected by the operator when performing a gradient recalled echo sequence? - Answer Flip angle, TR, TE In order to produce images based on differences in T1, the time interval between 90-degree excitation pulses should be: - Answer Short how does signal from cerebral spinal fluid appear on a standard short TR & short TE, Spin echo pulse sequence in which no suppression techniques have been used? - Answer Dark - T1 water & CSF appear dark How does signal from fat appear on a standard short TR & short TE, SE pulse sequence in which no suppression techniques have been used? - Answer Bright - Fat is bright on T1 How does signal from CSF appear on a standard long TR & Long TE. Spin echo pulse sequence in which no suppression techniques have been used? - Answer Bright - water appear bright on T2 In gradient echo imaging what parameters control the amount of T1 wieghting of the images? - Answer TR & Flip angle To be considered a T2 weighted image the TE range of a SE sequence shoulde be: - Answer 80 to 120ms As the TE is increased the signal intenstity of successive SE will: - Answer Decrease in a gradient echo pulse sequences a steady state is achieved & in the condition the TR is: - Answer Less than the T1 & T2 of the tissues When doing a coherent gradient echo pulse sequence that is T2* weighted in order to maintain the steady state the flip angle should be in the range of: - Answer 30 to 45 degrees There are two methods to acheive RF spoiling with a gradient echo sequence that relies on incoherent residual transverse magnetization. They are used mainly to produce what type of image? - Answer T1 When performing a conventional gradient echo sequence with a flip angle of 60 degrees. What type of images will be produced? - Answer T1 weighted When doing a fast gradient echo sequence, one way to decrease the sequence time is by increasing the receiver bandwidth. However what would be the disadvantage to this? - Answer Reduce SNR the driven equilibrium tissue prepared gradient echo sequences will produce what type of image contrast? - Answer T2 A gradient echo image with a Flip angle of 10 degrees will exhibit what type of contrast? - Answer T2-the larger the flip angle increase the degree os saturation therefore T1 contrast is increased