via application of a magnetic gradient orthogonal to the slice of interest

via elimination of the B0 magnetic field everywhere except within the slice of interest

via application of the RF pulse only within the slice of interest.

via tipping of the B0 magnetic field into the plane of the slice of interest

via application of a 180◦ RF pulse

The Larmor frequency of hydrogen varies slightly for different chemical environments such as fat and water, accounting for the chemcial shift artifact.

Manipulation of the gradient coils can produce frequency or phase encoding of location.

The observed signal in MRI is an RF signal produced by the rapidly rotating transverse magnetization.

All are true.

The protons in hydrogen accounts for almost all clinical MRI imaging.

All are true.

It is generally used to establish coordinates in the third dimension (y), after slice selection and frequency encoding have established coordinates in the other two dimensions (z and x, respectively).

It is accomplished by activating a phase-encode gradient for a certain amount of time to add a “twist” proportional to distance along the phase-encode dimension. A series of these are collected each with a different amount of phaseencode gradient.

Phase encoding capitalizes on the different magnetic resonance properties in solid vs. liquid phases of small domains of hydrogen atoms in tissue.

It typically results in a rectilinear traversal of k-space, permitting direct application of the inverse Fourier transform.

None is true.

It decreases with increasing magnetic field.

It is dependent on magnetic field but independent of the particular atomic number and atomic mass (for example, 1H vs. 13C)

It is dependent both on the local magnetic field (to which it is proportional) as well as the particular atomic number, atomic mass, and chemical environment of the atom (which determine the proportionality, the gyromagnetic ratio).

Itisdependentonlyontheatomicnumberandmassoftheparticularelementbutnotonthechemicalenvironment that atom.

I and II

I and III

only I.

II and III

I, II, and III

I and II

I, II, and III

only I.

II and III

I and III

MR does not expose the patient to ionizing radiation, while CT does.

CT can make use of contrast agents whereas MR cannot

MR is better for imaging soft tissues, while CT is better for imaging bone.

All are true

MR is more expensive than CT.

None.

I and III

I and II

II and III

I, II, and III

only I.

I and II

II and III

I and III

I, II, and III

Both use π RF pulses and then wait for an appropriate amount of time before applying a π/2 RF pulse, when a particular tissue type has recovered just enough of its longitudinal magnetization to have reached a “null” point.

They each suppress a particular tissue type with a specific T1.

All are true.

STIR is used to suppress fat, for example, to see tumors in the breast.

FLAIR is used to suppress watery fluids such as cerebral spinal fluid (CSF), for example, to visualize high-intensity objects in the ventricles.

It can be covered in a polar fashion by using a series of read gradients with different x and y components, in which case filtered back projection is required to “fill in” the high frequencies.

It can be covered rectilinearly using phase encoding, in which case an inverse Fourier transform can recover the image.

The term arises from the convention in physics where wave number k represents a spatial frequency.

If we can cover all of k-space, we can recover the image of the corresponding slice.

All are true.

All are true.

It is applied during the acquisition of the RF signal.

It permits localization by using the Fourier Transform.

It is immune to spatial error from chemical shift artifact.

It causes the Larmor frequency to vary across the slice, producing a spectrum of frequencies.

None of the other statements is true.

CT images bone differently from soft tissue whereas MRI does not.

CT is a tomographic modality whereas MRI is not.

MRI uses ionizing radiation whereas CT does not.

MRI is a tomographic modality whereas CT is not.

It has become commonplace in recent years, and generally considered safe.

It is dangerous because of occasional high iron content of the placenta, but may be used if this condition can be excluded.

It is never used at all on pregnant patients

Its associated risks to the fetus are considered significant, but occasionally worth it in extreme cases.

It cannot be justified because of its expense.

All are true.

It is applied during the acquisition of the RF signal.

It permits localization by using the Fourier Transform.

It causes the Larmor frequency to vary across the slice, producing a spectrum of frequencies.

It is applied during the 90◦ RF pulse.