Question: Why does the net magnetization (M) of an unmagnetized sample of material placed in a magnetic field not initially develop transverse components?

Choices:
- This premise of the question is false; M develops transverse components from the very beginning.
- The transverse components are not seen at first because they take several seconds to develop.
- The transverse components are neutralized by the precession of M.
- The individual spins contributing to M have randomly dispersed transverse components lacking phase coherence.

The NMR Phenomenon Quiz

Answer d) is correct because the spins have random transverse components of angular momentum. An RF-pulse or energy input near the Larmor frequency will be necessary to generate some phase coherence and transverse components.  Link to Q&A discussion


Question: What intrinsic tissue parameter determines the rate at which the longitudinal component of the net magnetization (M) initially develops?

Choices:
- Spin density (ρ)
- T1
- T2
- T2*

The NMR Phenomenon Quiz

The initial growth of longitudinal magnetization (Mz) is a simple exponential with time constant T1.


Question: Which of the following statements concerning net magnetization (M) is false?

Choices:
- Net magnetization (M) develops when an unmagnetized sample of tissue is placed in an external magnetic field.
- Initially M grows in the longitudinal direction as the individual spins seek to align with B0.
- When tipped out of alignment with B0, M will precess at the same resonance frequency as the individual nuclei comprising it.
- M will continue to precess even when completely inverted and pointing in the −z direction (i.e. opposite to B0).

The NMR Phenomenon Quiz

Only d) is false. Even though the individual spins comprising M are always precessing, M itself does not precess unless tipped out of alignment with B0 allowing it to develop nonzero transverse components. Once M is completely inverted 180° with respect to B0, it no longer has transverse components and is no longer precessing. If left alone after such an inversion, M will simply regrow along the z-axis to return to its initial orientation and magnitude aligned with B0.


Question: Which of the following statements about nuclear magnetic resonance is false?

Choices:
- Tipping the net magnetization (M) out of initial alignment with B0 requires absorption of energy by the spin system.
- In MRI, the source of energy required to initiated NMR is typically provided by a rotating/oscillating radiofrequency field named B1.
- This tipping of (M) is a manifestation of the NMR phenomenon.
- Nuclear precession and resonance are essentially the same.

The NMR Phenomenon Quiz

All statements are true except d). Nuclear precession is experienced by all non-zero spin particles when placed in an external magnetic field and requires no input of energy. NMR is a special condition of a spin system requiring the absorption and release of energy over a narrow range of frequencies.


Question: Which of scientist first experimentally demonstrated the NMR phenomenon in the 1930's and gave it its name?

Choices:
- Felix Bloch
- Isidor Rabi
- Edward Purcell
- Peter Mansfield

The NMR Phenomenon Quiz

Isidor Rabi is credited with naming NMR and being the first to demonstrate its existence experimentally in a molecular beam of LiCl.


Question: Which of the following statements about the NMR discoveries of Felix Bloch and Edward Purcell is true?

Choices:
- The two worked together in adjacent labs at Harvard.
- Their experimental setups were nearly identical.
- Their initial reports were published simultaneously in 1946.
- Only Bloch received the Nobel Prize for his research.

The NMR Phenomenon Quiz

Bloch performed his research at Stanford at the same time Purcell was working independently at MIT. Their experimental setups were quite different, Bloch detecting an induction signal from water and Purcell measuring energy absorption in solid paraffin wax. Their initial reports were published simultaneously in the January, 1946 issue of the journal Physical Review, so answer c) is true. Bloch and Purcell jointly received the Nobel Prize for Physics in 1952.


Question: The radiofrequency (RF) field used to inject energy into a spin system to induce nuclear resonance is called

Choices:
- B0
- B1
- B2
- Mxy

The NMR Phenomenon Quiz

The correct answer is B1. B0 is the main magnetic field and Mxy are the transverse components of net magnetization induced by B1. There is no field called B2.


Question: (Advanced) Which of the following statements concerning the spin-system immediately after a 90°-pulse is true?

Choices:
- If the z-component of angular momentum were measured for all protons, an equal number of spin-up and spin-down states would be observed.
- The 90°-pulse causes the spins to precess around B1.
- The spins all become locked into phase coherence with one another.
- The spin angular momentum for each proton is turned so that it points horizontally in the direction of B1.

The NMR Phenomenon Quiz

This is a pretty tricky question that really probes one's understanding of the NMR phenomenon. Only a) is true. If the longitudinal angular momentum of all spins were measured (by passing them through all Stern-Gerlach device, for example), an equal distribution of spin-up and spin-down states would be observed. Remember that spins do not exist in pure eigenstates, so it is not correct to say there are an equal number of spin-up and spin-down protons (though that statement is commonly found in textbooks). But the idea is much the same. Option b) is false, but only barely so. Precession after a 90°-pulse occurs around the direction of B0, just as it did prior to the RF-pulse. During the application of the RF-pulse, however, procession occurs around both B0 and B1, described in more detail in the Q&A's about the rotating frame.  Option c) is false, as no "magical" locking together of spins occurs. What we call "phase coherence" is simply the same initially skewed longitudinal distribution of spin energies that have been rotated into the transverse plane by the RF-pulse. Finally, option d) is false. By the Heisenberg uncertainty principle we cannot know the direction a spin is "pointing", so the statement is meaningless. But I'm pretty sure the spins would not all be "pointing" horizontally if we were able to know!


Question: The complex motion of the net magnetization vector (M) when acted upon by both B0 and B1 can be simplified by considering the system in the

Choices:
- Laboratory frame of reference.
- Rotating frame of reference.
- Earth's frame of reference.
- Adiabatic frame of reference.

The NMR Phenomenon Quiz

The rotating frame of reference allows the motion of (M) to be simplified by removing the simple Larmor precession around B0. It's like riding on a merry-go-round instead of watching it from stationary ground nearby.


Question: (Advanced) What happens if the B1 field is not applied exactly at the Larmor frequency?

Choices:
- Spins will not be affected and will continue to precess only around B0.
- Spins will stop precessing around B0 and begin to precess around B1.
- Spins will precess around an effective field Beff in the rotating frame that takes into account of off-resonance B1 and B0 effects.
- The spin system will experience random and unpredictable fluctuations in energy levels.

The NMR Phenomenon Quiz

The correct answer is c). It describes the "off-resonance" condition which is commonly encountered in MR imaging where a span of RF-frequencies is transmitted and gradients affect Larmor frequencies across the object being imaged.


Question: (Advanced) Which of the following statements about adiabatic excitation is false?

Choices:
- Unlike "conventional" RF-pulses that are purely amplitude-modulated, adiabatic RF-pulses are also frequency-modulated.
- The fat-suppression technique SPAIR uses adiabatic inversion.
- Adiabatic pulses are relatively insensitive to B1 field inhomogeneities.
- Doubling the duration of a 90°-adiabatic pulse creates a 180°-adiabatic pulse.

The NMR Phenomenon Quiz

All statements are true except d). Unlike "conventional" RF-pulses, the flip angle of an adiabatic pulse is NOT proportional to its magnitude and duration. An adiabatic pulse cannot be easily scaled or stretched to change its effect.


Question: Which of the following is not a synonym for T1 relaxation?

Choices:
- Spin-spin relaxation
- Spin-lattice relaxation
- Longitudinal relaxation
- Thermal relaxation

The NMR Phenomenon Quiz

Spin-spin relaxation is a synonym for T2 relaxation.


Question: Which of the following is/are synonyms for T2 relaxation?

Choices:
- Spin-spin relaxation
- Transverse relaxation
- Thermal relaxation
- Both a) and b)

The NMR Phenomenon Quiz


Question: Which of the following statements about T1 relaxation is false?

Choices:
- T1 is the time constant for regrowth of longitudinal magnetization (Mz).
- T1 relaxation requires an energy transfer between spins and their environment ("lattice").
- T1 relaxation results in a net energy loss from the spin system.
- This energy loss occurs by spontaneous emission of photons from the protons.

The NMR Phenomenon Quiz

All are true except d). T1 relaxation requires release of absorbed energy from the spin system to the external environment, but this such energy transfer must be stimulated by interaction with a fluctuating field near the Larmor frequency arising from a nearby proton or molecule.


Question: When an unmagnetized sample is placed in a magnetic field, an internal magnetization (M) will develop and grow to a maximum value in the longitudinal direction (M0). The first order exponential time constant for this growth is defined as

Choices:
- T1
- T1*
- T2
- T2*

The NMR Phenomenon Quiz

This is the definition of T1 as described by Felix Bloch.


Question: T1 is the time required for the longitudinal magnetization Mz to grow from zero to about ____ of its maximum value (M0)

Choices:
- 0,37
- 0,5
- 0,63
- 1

The NMR Phenomenon Quiz

The equation for exponential regrowth is Mz = M0 (1 − e−t/T1). After one time constant (i.e., at t = T1), Mz will have reached (1 − e−1) or about 63% of its maximum value (M0). Link to Q&A discussion


Question: T2 is the time required for the transverse components of magnetization M0 to decay to approximately ____ from their maximum initial value after a 90°-pulse.

Choices:
- 0,37
- 0,5
- 0,63
- 1

The NMR Phenomenon Quiz

The equation for exponential decay of transverse magnetization immediately after a 90°-pulse where the initial magnetization (M0) has been tipped into the transverse plane is given by: Mxy = M0 e−t/T2. After one time constant (i.e., at t = T2), Mxy will have decayed by (e−1) or to about 37% of its initial value.


Question: Which of the following statements concerning T2 relaxation is false?

Choices:
- Any process causing T2 relaxation also results in T1 relaxation.
- A major cause of T2 relaxation is dephasing of spins by static local field inhomogeneities.
- Another major cause of T2 relaxation is spin-spin "flip-flop" interactions.
- T2 relaxation may occur with or without energy transfer/loss from the spin system.

The NMR Phenomenon Quiz

Only a) is false, but its converse is true, "Any process causing T1 relaxation also results in T2 relaxation". The other options are correct.


Question: If the T1 relaxation time for brain tissue is 1000 ms, what is its relaxation rate (R1)?

Choices:
- 1000 msec
- 1 sec
- 1 sec−1
- 1 msec−1

The NMR Phenomenon Quiz

Relaxation rate is merely the inverse of relaxation time. So R1 = 1/T1 = 1/1000 msec = 1/(1 sec) = 1 sec−1


Question: Which of the following relaxation time pairs for tissue is impossible?

Choices:
- T1 = 4000 ms, T2= 2000 ms
- T1 = 1000 ms, T2 = 100 ms
- T1 = 500 ms, T2 = 20 ms
- T1 = 500 ms. T2 = 600 ms

The NMR Phenomenon Quiz

Because every process that causes T1 relaxation also causes T2 relaxation, but T2 relaxation can occur without T1 relaxation, T2 is always less than or equal to T1. Thus the combination in choice d) is impossible.


Question: Which of the following biological materials would be expected to have the shortest T2 values?

Choices:
- Urine
- Achilles tendon
- Spleen
- Liver

The NMR Phenomenon Quiz

T2 relaxation occurs most quickly when local static magnetic fields are present that dephase the spins. The more "solid" and "drier" the tissue, the shorter is its T2 value. Of the choices above, tendon has the shortest T2.


Question: Which of the following biological materials would be expected to have the shortest T1 values?

Choices:
- Scalp fat
- Pus
- Liver
- Spleen

The NMR Phenomenon Quiz

Because of their size and shape, triglycerides (the main component of adipose tissue as in scalp fat) have a relatively large fraction of molecular motions near the Larmor frequency, making them efficient at T1 relaxation. So the correct answer is a). Yellow bone marrow has relatively short T1 due to fat deposition, but red marrow has much less fat and is filled with water-containing hematopoietic cells.


Question: Which of the following biological materials would be expected to have the longest T2 values?

Choices:
- Colloid cyst in the thyroid
- Pus
- Urine in the bladder
- Kidney

The NMR Phenomenon Quiz

Free or "unbound" water molecules tumble most rapidly averaging out static dipolar interactions and hence have the longest T2 values. So pure liquids like spinal fluid and urine have the longest T2 values.


Question: Which of the following statements about T2* is false?

Choices:
- T2* is always longer than T2.
- T2 is always longer than T2*.
- T2* includes not only "true" T2 effects but also effects of magnetic field inhomogeneities.
- T2* includes not only "true" T2 effects but also effects of magnetic field inhomogeneities.

The NMR Phenomenon Quiz

T2* includes not only "true" T2 effects but also effects of magnetic field inhomogeneities.


Question: Which of the following molecular mechanisms is the most important for causing T1 and T2 relaxation in ¹H NMR?

Choices:
- Dipole-dipole interactions
- Chemical shift anisotropy
- Chemical shift anisotropy
- Molecular translation/diffusion

The NMR Phenomenon Quiz

All these mechanisms make contributions, but the dipole-dipole interaction is the most important. Dipole-dipole interactions are "through space" magnetic field disturbances typically occurring between nuclear or electron spins on the same or closely apposed molecules.


Question: In dipole-dipole interactions, T1 relaxation is most efficient (and T1 values are shortest) for

Choices:
- Small, rapidly tumbling molecules
- Molecules tumbling near the Larmor frequency
- Large, slowly moving molecules
- Macromolecules bound to a rigid biologic scaffold or matrix

The NMR Phenomenon Quiz

Since T1 relaxation requires stimulated energy exchange at the Larmor frequency, spins on molecules tumbling at near the Larmor frequency are most efficient at T1 relaxation.


Question: In dipole-dipole interactions, T2 relaxation is most efficient (and T2 values are shortest) for

Choices:
- Small, rapidly tumbling molecules.
- Molecules tumbling near the Larmor frequency.
- Large, slowly moving molecules.
- Macromolecules bound to a rigid biologic scaffold or matrix

The NMR Phenomenon Quiz

Stationary local magnetic fields are most effective at inducing T2 relaxation, so nearly immobile macromolecules (especially those bound to bones, cell membrane, or collagen) have the shortest relaxation times of all. Small, rapidly tumbling molecules have very long T2 values.


Question: Considering the effects of macromolecules on relaxation times, which of the following is false

Choices:
- Macromolecules themselves often have extremely short T2 values and their signal may decay too quickly to be detected using conventional MRI techniques.
- A "bound" or "hydration" layer of water molecules with restricted motion is generally found adjacent to macromolecules.
- These "bound" water protons interact exclusively with macromolecules and not with the "free water" pool.
- Bound water molecules tumble more slowly, producing shortening of T1 and T2. This partially explains the reduced T1 and T2 values of tissues compared to free water.

The NMR Phenomenon Quiz

Only c) is false. The bound water molecules interact and exchange magnetization both with the macromolecules and the free water pool.


Question: Which of the following ¹H-containing molecules account for nearly 100% of the signal recorded within the brain parenchyma using routine MRI sequences?

Choices:
- Water
- Triglycerides
- Myelin
- N-acetyl aspartate (NAA)

The NMR Phenomenon Quiz

Triglcerides are present in scalp fat, but not in the brain parenchyma itself. Myelin is  present in the brain, but as an immobile macromolecule has an extremely short T2 and whose signal thus decays too rapidly to be detected using conventional MRI sequences. NAA is the brain metabolite with the largest peak seen on MR spectroscopy of the brain, but its concentration is many thousand times lower than that of water.


Question: By irradiating tissue with an off-resonance RF-pulse it is possible to affect image contrast by transferring energy between macromolecular and free-water pools. This process is known as

Choices:
- T1 exchange
- Magnetization transfer
- Chemical shift
- Energy swap

The NMR Phenomenon Quiz

This is a brief description of MT.  Link to Q&A discussion


Question: As field strength increases from 0.5T to 3.0T, the T1 of most tissues

Choices:
- Increases
- Decreases
- Remains about the same
- Decreases then increases

The NMR Phenomenon Quiz

For most biological tissues, empirical measurements suggest that T1 increases approximately as B0⅓. Therefore, measured T1 values of most tissues will approximately double as field strength is raised from 0.3 T to 3.0 T.


Question: As field strength increase from 0.5T to 3.0T, the T2 of most tissues

Choices:
- Increases
- Decreases
- Remains about the same
- Decreases then increases

The NMR Phenomenon Quiz

The effect varies depending on tissue type, but generally there is relatively little change in T2 values over the 0.5T to 3.0T range. T2 definitely shortens for fields > 3.0T, however.


Question: The MR signal in adipose tissue comes primarily from hydrogen protons in

Choices:
- Free fatty acids
- Long-chain triglycerides
- Short-chain triglycerides
- Cholesterol

The NMR Phenomenon Quiz

The major MR signal in adipose tissue comes from long-chain aliphatic triglycerides, 16-20 carbon atoms in length, that are mostly saturated (−(CH2)n−).


Question: Protons in which lipid elements do not contribute significantly to the bright MR signal of fat on routine T1-weighted imaging?

Choices:
- Cell membrane phospholipids
- Liquid forms of cholesterol
- Free fatty acids
- Triglyceride methyl groups

The NMR Phenomenon Quiz

Phospholipids and sphingolipids, present in cell membranes and myelin respectively, have exceedingly short T2 values and their MR signal is not directly recorded using routine MR sequences. They can be recorded using ultrashort TE (UTE) methods.


Question: Examples of bright T1 signal due to exogenous lipids include all of the following except

Choices:
- Intrathecal Pantopaque™ from myelography in the 1980s
- A commercial MR skin marker
- A vitamin E capsule skin marker
- Vaseline (petroleum jelly) on the skin

The NMR Phenomenon Quiz

Although vitamin E capsules, fish oil capsules, and bath oil beads may be used as skin markers in MRI, they cannot be seen on fat-suppressed images. Commercial MR skin markers contain a dilute paramagnetic solution visible on all pulse sequences. Link to Q&A discussion


Question: Why do areas of microcalcification sometimes appear bright on T1-weighted images?

Choices:
- The calcium nucleus also undergoes NMR and mixes with the ¹H signal
- You are seeing a susceptibility artifact, not a true change in relaxation time
- Interaction with salts on porous calcium surfaces slows rotation of water molecules
- Microcalcifications often have fat-containing bone marrow within them

The NMR Phenomenon Quiz

The high signal is not coming from the calcium itself, as Ca is an even-numbered element with zero spin and no intrinsic MR signal.  The signal is coming from water protons, whose molecular rotation rates have been slowed to near the Larmor frequency by surface interactions with the calcium salts.  This rotational slowing results in short T1 and hence brightness on T1-weighted images.


Question: The T1-bright signal of meconium is primarily due to

Choices:
- Paramagnetic minerals
- Free fatty acids
- Carbohydrates
- Mucin

The NMR Phenomenon Quiz

Although several physical properties contribute to the relaxation times of meconium, the dominant process is likely the accumulation of paramagnetic (Fe, Mn, Mg) minerals within it.  Meconium also contains free fatty acids, carbohydrates, and mucin, but their effects on T1 relaxation are thought to be minor.


Question: The “magic angle” effect takes place when two magnetic dipoles form an angle of about how many degrees with each other?

Choices:
- 30º
- 45º
- 55º
- 60º

The NMR Phenomenon Quiz

The dipolar interaction due to the static field vanishes at the magic angle of approximately 54.7º.


Question: Interaction of two dipoles at the magic angle affects

Choices:
- T1 only
- T2 only
- T1 and T2
- Neither T1 nor T2

The NMR Phenomenon Quiz

The magic angle effect lengthens T2 with theoretically no effect on T1.


Question: Which tissue in the list below does not normally demonstrate signal changes on MRI due to the magic angle effect?

Choices:
- Liver
- Tendon
- Cartilage
- Peripheral nerve

The NMR Phenomenon Quiz

The magic angle effect is important in the clinical MR imaging of certain tissues that are highly structured and are oriented obliquely to the main magnetic field (especially tendons, cartilage, and peripheral nerves). The MR signal may spuriously increase near the magic angle mimicking pathology. Liver has no single direction anatomic structure and would not display a magic angle effect.