Understanding MRI Enhancement: Mechanisms, Magnetic Fields, and Contrast Agents, Exams of Nursing

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The effects of main magnetic field inhomogeneities on the FID signal are corrected for in a Spin-echo sequence by applying a second radio-frequency pulse. The flip angle of this radio-frequency pulse is: 180 degrees Of the following statements, which describes part of the basic MR imaging process? Radio-frequency signals interact with hydrogen protons Which type of electromagnetic coils correct inhomogeneities in the main magnetic field? Shim coils Immediately after an initial 90 degree radio-frequency pulse is turned off, the hydrogen protons will begin to: Dephase Tissues that are very efficient at Spin-lattice interactions near the Larmor frequency, such as fatty tissues, should have: Low T1 values and produces hyperintense signals T1 is the measurement of time for the longitudinal component of the net magnetization vector to recover what percentage of its original value after the application of a 90 degree radio-frequency pulse? 63% The tissue characteristic which depends more on the state (solid, liquid, gas) of a tissue than any other factor is: T2 effects The basic process of MR signal generation contains two basic steps, they are: Stimulation and relaxation The T1 Process is also known as: Spin-Lattice

The T2 process is also known as: Spin-Spin Once in the main magnetic field, a majority of hydrogen protons will align themselves: Parallel to B Magnetic resonance imaging is derived from the process known as: Nuclear magnetic resonance The tissue characteristic that depends heavily on the relative content of fat molecules and free water is: T1 effects Which type of receiver radio-frequency coil is placed close to the patient's body for the purpose of imaging superficial anatomic structures? Surface coils An equation derived to predict the MR signal intensity of a particular tissue as a result of a spin-echo pulse sequence is the: Larmor equation Which equation is true of the relaxation process? Without the effects of T2 star, T2 decay continues Because of the spinning motion of the hydrogen proton it has the same properties as a bar magnet. The hydrogen proton's spinning motion gives it a: Magnetic moment On a proton density image, two types of tissue that contain very low concentrations of hydrogen appear very hypointense are: (RESEARCH THIS) Cortical bone and lung (RESEARCH THIS) Magnetic susceptibility is defined as: (RESEARCH THIS) Tendency of a substance to attract or repel magnetic lines of force which is decided by the magnetic properties of its electrons (RESEARCH THIS) In comparison to computed axial tomography, an advantage of MR is: Superior soft-tissue contrast resolution Fast transition phenomenon and entry phenomenon are theories that explain which of the following tissue characteristics? Velocity effects

In 1990 Lauffer described two types of contrast media, the mechanism of the T1 agent is to D) decrease T1 relaxation time, this emitting high signal. For the following spin echo protocol: fov 320/TR 500/ TE 25/ slice thickness 5mm/ slice gap 1 mm/ NEX 4/ matrix 192. Increasing the Field of View will Increase SNR What factor, in spatial localization, does the slope of the slice select gradient? Slice thickness What is the gyro-magnetic ratio of hydrogen 42.58MHz For the followong spin echo protocol. FOV 320/ TR 500/ TE 25/ slice thickness 5mm/ slice gap 1mm/ NEX 4/ matrix 192. Decreasing slice thickness will Decrease SNR The Process of relaxation begins when B1 is turned off A sinewave is a symbol used to measure electromagnetic energy. A sinewave's two components of measure are: Wavelength and frequency Magnetic fields have direction which are usually designated as north and south, therefore magnetic fields are described as: Dipoles At any one time, human body tissue, in general, is made up of 50-90%: H(Hydrogen) Once the net magnetization vector (NMV) has moved away from equilibrium the following will occur: The transverse component will increase The T1 process is also known as: Spin-Lattice Which of the following is the Larmor equation? W0=Y+B The mechanism of T2 contrast enhancement agents is to:

Decrease T2 relaxation time, therefore producing low signal Which type of MRI magnet requires cryogen to cool magnetic coils to 4 degrees Kelvin? Superconductive A time constant that characterizes the fast rate of transverse magnetization because of the inhomogeneities of the main magnetic field is: T2* As the net magnetization vector precesses within the transverse plane, it induces an electrical current in a: Radio-frequency coil To symbolize the flow and area of a magnetic field, lines are used which are called: Field or flux All chemical substances have an assigned constant known as the: Gyro-magnetic ratio. MRI systems require rooms that provide specific shielding requirements. These rooms are lined with what types of materials? Copper or galvanized steel Which type of MRI magnet requires no electricity to maintain its magnetic field and can weigh from 18,000 lb to 200,000 lb? Permanent An equation derived to predict the MR signal intensity of a particular tissue as the result of a Spin-echo pulse sequence is the: Larmor equation At any one time, human body tissue, in general, is made up of 50-90% of what substance? H(Hydrogen) Tissues that are very efficient at spin-lattice interactions near the Larmor frequency, such as fatty tissues, should have: Low T1 values and produces hyperintense signals. A sinewave is a symbol used to measure electromagnetic energy. A sinewave's two components of measurement are: Wavelength and frequency Tissues that are efficient at both T1 and T2 interactions have low (short) relaxation times, and therefore have:

B) gradient field strength The primary function of the anterior cruciate ligament is to prevent C) anterior movement of the tibia The FDA recommends warning signs to make the which gauss line? A)5 Gauss line In spatial localization, phase encoding is performed B)Prior to frequency encoding In regards to radio frequency (RF), the concern is that there should not be an increase in the body for temperature of B) 1 degree Celsius Fast blood flow will have___blank___ and appear___blank___ C) very little signal/ dark The components of the gyro-magnetic ratio are Magnetic moment to angular momentum During 2DFT, spin echo pulse sequences, fast flowing blood usually appears C) hypointense Slow blood flow will have blank and appear___blank___ A) hyperintense signal/ bright The recieve bandwidth is related to the slope of which gradient? C) frequency encoding When under going T1 relaxation, the net magnetization vector will? Realign with the Z axis The most commonly noted reaction to intravenous administration of gadolinium cheated is C) HA Different tissues that have signals that appear similar on an MRI image are described as Isointense In a pulse sequence employing 4 NEX, to increase SNR by 100% you would have to increase the NEX to E) 16 Measured by T1 values at 1.5T will be___blank___ at 0.5T

B)Greater than The best imaging plane for visualization of the neural foramina is D) parallel to the intervertebral disks During 2DFT, spin echo pulse sequences, slow flowing blood usually appears A)Hyperintense A sudden loss of superconductivity with explosive boiling off of liquid helium is called C) quench Following the excitation pulse, the FID decays Exponentially Nuclei that lose phase coherence? Decrease MR signal In a large main magnetic field such as those employed in MRI, the motion of a hydrogen proton had been described as a wobbling-like spinning top. This motion is called Precession Increasing the number of phase encoding steps will produce an image with... Higher resolution Fatty tissues have a molecular structure that is very efficient at spin-lattice interactions at the larmor frequency, so fatty tissues should A) have short TI values and appear hyperintense Spatial resolution is an image quality factor determined by Slice thickness & pixel size A blank is defined as two magnetic poles of. Equal strength or magnitude, opposite in direction, and separated by an infinitesimal distance C) dipole SAR limitation problems are more likely to be experienced using which transmitter coil? A) body coil....SAR limits are less of a problem with the smaller FOV coils because the transmit lower RF power than larger FOV coils Once the net magnetization vector (NMV) has moved equilibrium, the following will occur The transverse component will increase

Mz In the USA, the MRI systems main magnetic field and the vector that represents it is symbolized B sub zero Which of the following parameters controls the amount of contrast seen in an image due to T relaxation: TE A magnetic field strength of 0.5T is equivalent to: 5000G An example of a dipole is: A hydrogen nucleus, a bar magnet, and the earth Hydrogen nuclei have a magnetic moment because they posses a property called: Spin Protons that aligned in the anti-parallel direction are in: A high energy state The formula that describes the relationship between the static magnetic field and the processional frequency of the hydrogen proton is the: Larmor equation To calculate the processional frequency, the strength of the static magnetic field is multiplied by a constant known as: The gyromagnetic ratio The field strength of an MR imaging magnet as measured within the bore is most typically expressed in terms of: Tesla The Larmor, processional or resonance frequency of hydrogen protons in a static magnetic field of 0.5T is approximately: 21.288 MHz Following RF excitation, as transverse magnetization (Mxy) decays to zero, The MR signal: Decays to zero RF pulses are identified according to the: Flip angle

Following the excitation pulse, the FID decays: Exponentially Of the following tissues, which has the longest T2 value Cerebrospinal fluid (1600) Of the following tissues, which has the shortest T1 value? Fat Nuclei in their natural environment (in absence of a significant magnetic field) are aligned: Randomly The characteristic time constant for loss of phase coherence or transverse magnetization due to static magnetic field inhomogeneities is known as: T2* Which characteristic of tissue, in MRI is the result of fast transition phenomenon and/or entry phenomenon: Flow/velocity effects MRI magnets that require a steady current of electricity passed through coils wrapped around an iron or air core are: Resistive MRI magnets that require cryogen's to cool a substance to approximately 4 degrees Kelvin are: Superconducting Coils that superimpose small magnetic fields within the patient during the MRI process and allow for spatial encoding are: Gradient coils Radio-frequency (RF) coils that are placed close to the patient's body specifically for the structures that are superficial and are receive only coils are: Surface coils A permanent magnet requires liquid helium and liquid nitrogen in a dedicated cooling system: False Employing a pulse sequence with a long TR and a long TE will result in tissues with a short T2 value appearing __ and tissues with a long T2 appearing __ on the resultant images: Dark/bright What factor, in spatial localization does the slope of the slice select gradient factor control?

T1; TR 100-1000ms, TE 20-30ms/ T2; TR 1600-3000, TE 70- The pulse sequence that replaces the second RF pulse with a magnetic field gradient to rephase the transverse vector and produce the echo signal is: Gradient Echo The artifact known as "cross-talk" can be corrected for by adjusting which parameter? Slice interval In terms of time, the least expensive parameter to increase, of those that affect time, when attempting to improve image quality: Matrix By increasing the parameter, Matrix, the size of the pixel will: Decrease Increasing which parameter is considered the "best" technique for improving image quality? NEX Of the following techniques, which one is applied to prevent "crosstalk" between multi-slices with little or no interslice "gap"? Interleaving The slice selection exposes the patient's body to a series of increasing or decreasing magnetic fields to select a slice. In what relation to the slice is this gradient introduced? Perpendicular Which method for providing spatial localization is employed during a pulse sequence when selecting only one slice at a time: 2DFT Which method for providing spatial localization is employed during a pulse sequence when selecting a volume of slices: 3DFT For MRI magnets, the specification for field homogeneity that is considered acceptable is: 20-30ppm The primary factor of an Inversion Recovery pulse sequence is which of the following parameters? TI Of the Different types of coils used in MRI, which type(s) are found only in the housing of the main magnet?

Shim/Gradient Which of the following causes artifacts on MR images is most commonly mistaken for pathological signal: Chemical shift Of the following anatomical structures which is considered to be normally enhancing post gadolinium injection? Choroid Plexus Cryogen levels should never fall below: 50% The electromagnetic coil responsible for producing the strong magnetic field of a superconducting magnet is embedded in a __ which serves as an insulator from heat in the event of a quench Copper matrix There are __ of __ serving the purpose of providing spatial information within the MR signal Three pairs/ Gradient coils The temperature of the liquid helium in which the electromagnetic coil is immersed is approximately: -436 F (-269 C) Cooling the electromagnetic coil windings to the point of superconductivity and then inducing an electric current from an external power supply until the magnet is at full power is called: Ramping- up Mri Magnets that can range from 26,000 to 2000,000 lb are: Permanent Following the injection of a gadolinium enhancement agent, the pulse sequence most commonly employed is a: T1 weighted All FDA approved gadolinium enhancement agents for MRI are administered at the same dose, it is: 0.1mmols/kg On MRI images, an acute hemorrhage will have a bright signal intensity in a T2 weighted pulse sequence: False Employing an Inversion Recovery pulse sequence with a water suppression technique, a normal intervertebral disc will appear dark: True

Enhancement can be demonstrated on which of the following pulse sequences post gadolinium injection: T1 weighted, gradient echo, inversion recovery SAR (Specific Absorption Rate), set by the FDA, is the rate that the RF energy is introduced to the body tissue, measured in watts per kilogram: True The maximum exposure of the head and trunk to the main magnetic field (B0), is: 3T The maximum exposure of extremities to the main magnetic field (B0) is: 5T Exposure to gradient magnetic fields are based on the premise that the fields should be too weak to cause neuromuscular stimulation by at least a factor of three (3): True Maximum exposure to gradient magnetic fields are set at a rate of 6T/second The maximum exposure to Radiofrequency (RF), averaged over the head is: No more than 3.2 w/kg The maximum exposure to Radiofrequency (RF), in one gram of tissue is: A maximum spatial peak of 8 w/kg In regards to Radiofrequency (RF), the concern is that there should not be an increase in the body core temperature of: 1 degree C Currently, patients and personnel are excluded from exposure to MRI for the 1st trimester of pregnancy: True Guidelines excluding pregnant individuals from MRI is mainly to protect the individual from: Radiofrequency (RF) Of the following categories of patients, the one that would not present any special safety considerations is: Patients with previous arthroscopic knee surgery Some older implanted ferromagnetic neuro-aneurysm clips, suture materials, and surgical clips will experience a force of __, as the material is passed through a strong magnetic field.

Torque The __ is a level of dose below which no response will be elicited: Threshold dose Local exposures to the Radiofrequency (RF) are: less than 38 degrees C in the head, Less than 39 degrees C in the trunk, less than 40 degrees C in the extremities: True Patients with cardiac pacemakers are only contraindicated for an MRI scan in main magnets of more that 0.5T (>0.5T): False Magnetophosphenes are described as: Seeing flashes of light Magnetically sensitive objects such as credit cards, magnetic tapes and discs, and EKG equipment should be kept beyond the __ gauss line: 5 Some fastened equipment such as pulse oximeters, and electrodes have been reported to cause 3rd degree burns: True Being a relatively new field in medicine, the radio-biological questions about MRI, including delayed response concerns, are still unanswered: True In the environment of an MR main magnetic field, most implants that cause a deflation are considered safe for imaging: False Once the MRI patient is comfortable and apparently has no problem with the overall procedure, is is acceptable for the technologist to leave the scanning area while a long scan is underway: False To avoid any possibility of a ferromagnetic object becoming a projectile, it would be advisable and safer to have the patient remove all metal objects from their person prior to the scan: True Given the tissue sample containing 10 mobile hydrogen protons, it can be safely assumed that approximately __ of those protons will __ to the static magnetic field: 10/ align parallel

C) T1 TR 100ms-1000ms, TE 20ms- 30ms. T2 TR 1600ms-3000ms, TE 70ms- 100ms. For the following spin echo protocol: FOV 320/ TR 500/ TE 25/ Slice Thickness 5mm/ Slice Gap 1mm/ NEX 4/ Matrix 192. Increasing the FOV, TE, & Slice Gap will Not affect scan time The effects of inhomogenieties on the FID signal are corrected for in a spin echo sequence by applying a second radio frequency pulse. The flip angle of this radio frequency pulse its 180 degrees Cooking the electromagnetic coil windings to the point of superconductivity and then inducing as electric current from an external power supply until the magnet is at full power is called Ramping up blank s the measurable magnetic resonance signal that occurs as the transverse magnetization decays to zero following the application off a 90 degree RF pulse C) free induction decay blank describes the condition reached within a few seconds of hydrogen being in a magnetic field D) equilibrium TE is defined B) the interval between the 90 degree pulse and the echo signal The term used to describe magnetic uniformity in the large static magnetic field is C) inhomogeniety The temperature of the liquid helium in which the electromagnetic coil is immersed is approximately? D) -436 degree Fahrenheit Measurement of the magnetic field strength outside the bore of the MR imager is most typically expressed in units of: Gauss Nuclei in their natural environment (in the absence of a significant magnetic field) are aligned: Randomly __ occurs when frequency of the RF pulse matches the frequency of the precessing nuclei: Resonance T2 is the characteristic time constant for: 63% loss of magnetization in the XY plane

The net magnetization vector will generate a stronger MR signal if the alignment is at: 90 degrees The __ and __ are terms which indicate the amount of macroscopic magnetization vector is rotated by an RF pulse with respect to the static magnetic field: Flip angle/ nutation angle Nuclei having an __ of nucleons (neutrons or protons) will tend to possess magnetic properties: Odd numbers Spin-lattice relaxation time is another term representing: T1 relaxation The tendency of a substance to become magnetized or to distort an applied magnetic field is: Magnetic susceptibility __ is the uniformity of the static magnetic field, expressed in terms of PPM (parts per million) over a defined volume Homogeneity Spin-spin relaxation is another term for: T2 relaxation __ is the property of most substances having paired orbital electrons resulting in these substances being weakly repelled by the applied magnetic field: Diamagnetic A spin-lattice occurs: The spinning nuclei begin to move out of the XY plane and realign toward the Z axis __ occurs when the frequency of the intermittent magnetic field, the RF pulse, matches the frequency of the precessing nuclei- the nuclei absorbing the energy of the RF pulse and flipping the nuclei at some alpha angle from the Z axis and into the XY plane: Resonance Because of a variation of only 10-15%, in most tissue, which tissue characteristic does not allow for much contrast resolution on MR images: Hydrogen concentration Raw data (digitized echoes) is loaded into the array processor in a 2D data acquisition matrix, commonly referred to as: K-space