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The NMV is rotated to the physical negative Z axis by applying a...? - ✔✔C)180 pulse Increasing which parameter is considered the "best" technique for improving image quality? - ✔✔C)NEX Studies have concluded that static magnetic fields up to what tesla produce no substantial harmful biological effects. - ✔✔C)2. Tissues that have low (short) relaxation times have: - ✔✔Higher relaxation rates Nuclei in their natural enviroment ( in the absence of a significant magnetic field) are aligned... - ✔✔Randomly Following the injection of a gadolinium enhancement agent, the pulse sequence most commonly employed is a... - ✔✔C)T1 weighted Employing a pulse sequence with a long TR & a long TE will result in tissues with a short T2 value appearing WHAT & tissues with a long T2 appearing WHAT on the resultant image. - ✔✔D)Dark/bright Which gradient axis direction is typically (for educational purposes) designated as the slice selection gradient? - ✔✔C)Logical Z gradient
Electromagnetic coils placed strategically to contain the fringe fields. - ✔✔2)Active shielding 1 milliliter of H2O contains how many hydrogen protons? - ✔✔ 6 ×10 to th 23power Which of the following statements is true for gadolinium MRI IV enhancement products? - ✔✔B) produces randomly fluctuating magnetic fields in its immediate enviroment. The maximum exposure to radiofrequency in 1 gram of tissue is: - ✔✔D) a maximum spatial peak of 8 w/kg Currently, patients & personnel arr exluded from exposure to MRI for the 1st trimester of pregnancy. - ✔✔True The maximum exposure to radio frequency averaged over the head is: - ✔✔B)No more than 3.2 w/kg The recieve signal amplitude for a pixel usually depends on thr substance's... - ✔✔A) T1, T2 , proton density Small magnetic field intoduced to the hydrogen protons in order to cause them yo move from the low energy state to the high energy state is... - ✔✔C) RF pulse at any one time, human body tissue, in general, is made up of 50%-90% of what substance? - ✔✔Hydrogen.
averaged over the head is answer 2. in one gram (1gr) of tissue is answer 3. - ✔✔1.C) no more than 0.4 w/kg 2.A) no more than 3.2w/kg 3 .B) maximum spatial peak if 8 w/kg on T1 weighted images sub-acute hemorrhage will appear bright? - ✔✔TRUE which characteristic of tissue, in MRI, is the result of fast transition phenomenon &/or entry phenomenon? - ✔✔flow/velocity effects radio frequency RF coils that are placed close to the patient's body specifically for structures that are superficial & are receive coils only are... - ✔✔surface coils chemical shift artifacts will show up on the image in what gradient direction? - ✔✔B) frequency encoding coils that superimpose small magnetic fields within the patient during the MRI process & allow for special encoding are... - ✔✔gradient coils In an Inversion Recovery pulse sequence what TI will produce STIR fat-suppressed pulse sequence? - ✔✔ 80 - 120 The Larmor precessional or resonance frequency of hydrogen protons in a static magnetic field of 0.5 is approximately... - ✔✔21.288 MHz
Residual, undesirable gradient magnetic fields that persist for a variable time duration after the pulse of electricity from the gradient power supply is terminated are known as... - ✔✔Eddy Currents which parameter in a pulse sequence helps to prevent "cross talk" between 2 adjacent images? - ✔✔Slice intervals Patients that have implants such as a pacemaker or neurstimulator should not go beyond the... - ✔✔ 5 gauss line when increasing the parameter matrix, the pixel size will... - ✔✔decrease once the MRI patient is comfortable & has no apparent problem with the overall procedure, it is acceptable for the technologist to leave the scanning area while a long scan is underway - ✔✔false the time interval between 90 degree RF pulses. - ✔✔TR the tissue characteristic which depends more on the state (solid, liquid, gas) of a tissue than other factor is... - ✔✔T2 effects after a 90 degree radio frequency pulse, the net magnetization vector begins to return to equilibrium. When NMV is half-way between transverse & equilibrium, what are the magnitudes of the longitudinal component & the transverse component? - ✔✔longitudinal component= greater than zero transverse component = greater than zero
In 1990 Lauffer described two types of enhancement media, the mechanism of the T2 agent is to... - ✔✔B)decrease T2 relaxation time, thus emitting low signal small magnetic fields that vary from strong to weaker predictably within the scan area of the patient bore... - ✔✔C) gradient magnetic field the purpose of magnetic resonance angiography is to image the... - ✔✔Blood flow Using the followong protocol, determine the scan time for this pulse sequence (rounding to nearest minute) FOV 320mm/ TR 2000ms/ TE 20 - 80ms/ NEX 1/ Matrix 250×120 - ✔✔4minutes. TR× NEX ×Matrix ÷1000 (sec) and agian ÷60 (min)... 2000× 1 × 128= 256, ÷1000= ÷60=4.2min The main magnetic field of the MRI System is described as constant and always oriented in one set direction, either horizontal or vertical (depending on magnet type). The transmitted radio frequency in comparison is described as - ✔✔Oscillating and always perpendicular to B sub zero
The gradient magnetic fields are - ✔✔A)Always on Of the following statements, which describes part of the basic MR imaging process? - ✔✔Radio frequency signals interact with hydrogen protons The basic process of MR signal generation contains two basic steps, they are... - ✔✔Simulation & relaxation In MR imaging, for a chemical substance to be affected by the main magnetic field and the radio wave, it must contain an... - ✔✔Odd number of total protons and neurons A pulse w sequence where only 90 degree RF pulses are used is called... - ✔✔D)Saturation recovery blank is the property of most substances having paired orbital electrons resulting in these substances being weakly repelled by the magnetic field. - ✔✔D) diamagnetic Which type of electro magnetic coils are designed to stimulate and detect an MR signal? - ✔✔Radio frequency coils The slice selection gradient exposes the body to a series of increasing or decreasing magnetic fields to select a slice. In what relation to the slice is this gradient introduced? - ✔✔D) perpendicular A pulse sequence that replaces the second RF pulse with a gradient magnetic field to rephase the transverse vector and produce an echo is called - ✔✔Gradient echo
The time decay between the original 90 degree RF pulse and the echo signal - ✔✔A) TE The H protons that are left over and parallel to B sub zero after equilibrium has been established - ✔✔Net magnetization What year was the first MRI enhancement agent approved for clinical use? - ✔✔A) 1988 Types of gadolinium used are - ✔✔D) all of the above. The difference in signal intensity between two adjacent structures is - ✔✔CNR Cryogen levels should never fall below - ✔✔50% The maximum exposure of the head and trunk to the main magnetic field is - ✔✔3T Of the following size molecules, which one will precess closer to the Larmor (resonance) frequency when placed within a large static magnetic field? - ✔✔B) medium ( fat) Different tissues that have signals that appear similar on an MR image are described as: - ✔✔Isointense In a large main magnetic field such as those employed in MRI, the motion of a hydrogen proton has been described as wobbling like a spinning top. This motion is called: - ✔✔Precession
Magnetic Resonance Imaging is derived from the process known as: - ✔✔Nuclear magnetic resonance Once the net magnetization vector (NMV) has moved away from equilibrium, the following will occur: - ✔✔The transverse component will increase In MRI, substances respond to a specific radio frequency which is known as: - ✔✔Resonance frequency The introduction of gadolinium based contrast enhancement agents by intravenous injection can involve passing through an abnormal brain barrier. The tissue compartments involved are the: - ✔✔Intravascular to interstitial T2 is the measurement of time for the transverse component of net magnetization vector to decrease what percentage of its maximum value after the application of a 90 degree radio-frequency pulse - ✔✔37% In the USA, the MRI system's main magnetic field and the vector that represents it is symbolized: - ✔✔B The resonance frequency of any substance in a magnetic field can be calculated by employing the - ✔✔Larmor equation Which type of electromagnetic coils are designed to stimulate and detect an MR signal? - ✔✔Radio- frequency coils
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
MRI magnets that must have a dedicated, special cooling system due to heat produced by large currents ( approx. 100-150 amps) are - ✔✔Resistive Substances which have magnetic properties of their own, such as methemoglobin or gadolinium, cause shortened T1 and T2 values for tissues in their vicinity are - ✔✔Paramagnetic Information acquired when you increase or decrease the frequency of the RF pulse of the Gs, ..... - ✔✔To be continued....... In MRI substances respond to a specific radio frequency which is known as - ✔✔Resonance frequency Effects associated with gradient magnetic fields in MR systems are - ✔✔A)Tissue hearing and cataract formation Possible effects of exposure to the transient radio frequency signals are - ✔✔B) tissue hearing and cataract composition Possible effects of exposure to the main magnetic field are - ✔✔D) magnetophosphenes, bones healing faster, cardiac fibrillation Relaxation from Resonance Begins set the time - ✔✔C) B sub 1 isturned off
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)
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: - ✔✔High relaxation rates Because of only a 10 - 15% variation in most tissues, the tissue characteristic that does not provide much contrast resolution is: - ✔✔Hydrogen concentration
The component Mz is most associated with: - ✔✔Parallel to B0; T1 relaxation; longitudinal magnetization The tissue characteristic that is dependent on the strength of the main magnetic field and temperature is: - ✔✔T1 effects The component Mxy is most associated with: - ✔✔Transverse to B0; T2 relaxation; transverse magnetization T2 is the measurement of the time for the transverse component of the net magnetization vector to decrease what percentage of its maximum value after the application of a 90 degree radio-frequency pulse: - ✔✔37% In the USA, MRI systems in clinical use have main magnetic field strengths that range from: - ✔✔0. Tesla to 3 Tesla On a very basic level, the three basic components required to attain MR signals are: - ✔✔Magnetic field, proton, radio-wave The main magnetic field of the MRI system is described as constant and always oriented in one set direction, either horizontal or vertical (dependent on type of magnet). The transmitted radio-frequency, in comparison, is described as: - ✔✔Oscillating and always perpendicular to B In a horizontal field magnet, what is the primary Gs for an axial slice? - ✔✔Gz
