MRI FINAL REVIEW

Which parameter adjustments would shorten scan time?

Decrease TR Increase echo train length Decrease NEX

How can we correct for a Gibb's artifact?

Increase number of phase encodings or decrease FOV

What can be done to the receiver bandwidth to compensate for chemical shift?

Increase receiver bandwidth

In an MRI system that uses shim coils, B0 homogeneity is adjusted by

changing current in the shim coil

DWI sequences are being tested for use in what?

characterizing liver lesion, imaging the left ventricle, imaging skeletal muscle injuries

Fat and water precess at different frequencies, causing a _________ artifact.

chemical shift

Hemangiomas of the liver are best visualized with:

contrast enhanced study with delayed images

In what plane would a tear of the collateral ligaments of the knee be best evaluated?

coronal

STIR sequences are typically used to evaluate:

fat suppression lesions within retro-orbital fat muskuloskeletal contusions compression fractures

Isotopes are a product of

fewer neutrons than protons

Chemical shift occurs primarily along which axis?

frequency

The gradient that is on during the production of the echo is the __________ encoding gradient

frequency

The gradient that is on longest is the __________ encoding gradient

frequency

The phase encoding step is performed prior to the ________ step

frequency encoding

The readout gradient is turned on during the sampling or readout of the peak echo and also during which other process?

frequency encoding

The stray magnetic field outside the bore of the magnet is termed

fringe field

Magnetic susceptibility artifacts are more prominent with ______ sequences

gradient echo

When imaging a hemorrhagic infarct in the brain, which pulse seuqence would best demonstrate the magnetic susceptibility effects?

gradient echo

Which protocol would be used to rule out islet tumors?

pancreas

Acquiring half the phase views of k space and then calculating the data for the other half is a technique known as

partial Fourier

In a super conducting magnet, the magnetic field strength is increased by increasing the

# of turns in the wires

A STIR sequence with a T1 time of 160 ms will null signal from fat at what field strength?

1.5 t

What best describes an inversion recovery sequence?

180 degree pulse followed by a combination of 90 degree and 180 degree pulses

To create a projection image in MRA, the technique MOST commonly employed is

19. maximum intensity pixel

If a given conventional spin echo pulse sequence takes 12 minutes to acquire, a multiecho sequence, using a 6 echo train, with all factors that affect scan time remaining the same, will take ________________ to acquire the same images

2 minutes

A major advantage of MRA over conventional angiography is that

2D time of flight

The MRA sequence that is more sensitive to slow flow is

2D time of flight

When using MRA to evaluate extracranial vascular flow, such as that within common carotid arteries, a recommended technique is

2D time of flight MRA

FDA revision in 2003 on RF absorption limits the absorption to ______ for the head

3 w/kg - 10 min

When using MRA to evaluate intracranial vascularity, flow within smaller vessels can best be demonstrated by

3D time of flight MRA or 3D phase contrast MRA

Reducing FOV by a factor of 2 will reduce the voxel volume by a factor of _____

4

What is the RF absorption limit for the whole body based off the 2003 FDA revision?

4 w/kg - 15 min

Using an NSA of 3, if a phase resolution of 192 is desired, then the TR must be repeated

576 times

If the desire is to null the signal from a specific tissue using an IR sequence, the TI selected should be _____% of the T1 relaxation time

69%

In a 3D acquisition, the slices are produced by

A phase encoding gradient applied in the slice direction. Acquired by volume imaging.

How can thin slices be selected?

Steep slice gradient narrow bandwidth

The common carotid bifurcates into the internal and external carotid artery at the level of ______

C3 / C4

Energy given to nuclei in adjacent slices due to spin lattice relaxation can cause adjacent slices in an acquisition to have different image contrast. What type of artifact is this?

Cross Talk

The four phases of a spin echo pulse sequence, in correct order, are

Excitation, encoding, refocusing, readout.

CSF suppression is performed with what sequence?

FLAIR

Calculate the pixel area for the following seuqence: TR 4000 TE 120 FOV 36 cm MATRIX 408 x 512 NEX 2 ETL 12

Formula: (FOV / MATRIX) x (FOV / MATRIX) = ____ mm (*remember to convert FOV from cm to mm by multiplying it by 10) (360/480) x (360/512) .075 x .0703 = ANSWER: .62MM

Choose the correct slice thickness to create an isotropic voxel for the following: TR2000 TE 90 matrix 272 x 272 FOV 24cm

Formula: FOV / matrix *remember to convert FOV from cm to mm by multiplying it by 10 240 / 272 = .88235 .88 slice thickness

Calculate imaging time for a patient with a heart rate of 90 b/min, trigger window 15% and trigger delay of 80ms.

Formula: TR - (trigger + delay) 1. Calculate TR (formula - 60,000 / b/mn = TR) 60,000 / 90 = 666 TR 2. Calculate trigger (formula - TR x trigger window %) 666 x 15% = 100 3. Imaging Time = TR - (trigger + delay) 666 - (100+80) 666 - 180 = 486 ms

In a FSE, what would scan time be for: 25cm FOV 224 x 320 matrix TR 2500 100 TE 3mm slice thickness 12 ETL 4 NEX

Formula: TR x Phase Matrix x NEX / ETL 2500 x 224 x 4 = 2240000 2240000 / 12 = 186666 *next, divide answer by 1000 to convert ms into sec 186.66 *next, divide by 60 to get mins and secs 3 min, 11 sec.

What would the scan time be in a 3D volume acquisiton as this: TR 24ms TE 7ms Flip angle 15 degrees FOV 20cm 2mm slice thickness 76 slices 176 x 256 matrix 1 NEX

Formula: TR x Phase matrix x NEX x # slices 24 x 176 x 1 x 76 = 321024 * next step, divide by 60,000 321024 / 60000 = 5.35 5 min / 35 sec

The process the digitizes the MR signal is known as:

Fourier / Fast Fourier

What is a Gibb's artifact?

Gibbs artifacts (also known as truncation, ringing, or spectral leakage artifacts) typically appear as multiple fine parallel lines immediately adjacent to high-contrast interfaces. These artifacts are particularly problematic in spinal imaging, in which they may artifactually widen or narrow the cord or mimic a syrinx.

If a patient has a history of back surgery with hardware that is MR safe, which sequence should NOT be used

Gradient echo

________ is more susceptible to metallic artifacts due to the lack of the 180 refocusing pulse that would reduce field inhomogeneities

Gradient echo

During a study for venout flow, where should the pre saturation pulse to applied to remove signal from arterial flow?

Inferior to the slice stack

Reducing the flip angle will result in images with what change in contrast?

Less T1

In a fast spin echo sequence, the effective TE is the echo that is performed with the

Low amplitude phase encoding gradient.

An artifact seen in a GRADIENT ECHO image that appears as black and white banding on the edges of the FOV

Moire

In a 2D multiecho pulse sequence, ETL = 8, scan time is given by the equation TR x

Number of signals averaged x number of phase encodings / the number of echoes.

Gadolinium chelates are

Paramagnetic.

All the following result in increased SNR

Parameter adjustments that increase SNR are: Increase TR Reduce phase matrix Increase FOV Reduce receiver bandwidth Increase NEX

Artifacts from motion will appear in which direction?

Phase encoding direction

Which sequence is most INSENSITIVE to magnetic field inhomogeneity?

SPIN ECHO

Which gradient echo sequence will give us TRUE T2?

SSFP (steady state free precession)

Which fissure divides the frontal lobe from the temporal lobes?

Sylvian

Cardiac cine acquisitions typically utilize a / an __________________ pulse sequence.

T1

The time it takes for a tissue's bulk longitudinal magnetization to return to 63% of its original value, following excitation, is known as

T1

When performing images of the brain to rule out a brain tumor, what images would be acquired post gad?

T1

Which is the best sequence to use to evaluate a patient with MS?

T2 FLAIR

The rate of dephasing due to inhomogeneities is called

T2 inhomogeneity

If a STIR sequence using a TR of 3000, a TE of 20, and a TI of 140 in a 1.5 T imager, produces an image with dark fat and bright water. The contrast in such an image is primarily based on

T2 weighted

Coherent gradient echo pulse sequences usually produce rapid images that are _____ weighted

T2*

The time it takes for transverse magnetization to decay to 37% of its original value, following excitation, is known as

T2*

In fast spin echo, the number of shots is calculated by what?

The # of phase encodings and echo train length

The medial and lateral rectus muscles are located where?

The eye

3D gradient echo axial views can be used in cervical spine imaging to provide

Thin, contiguous sections of the spine, the ability to reformat into any other imaging plane, retrospectively, the ability to get either T1, spin density or T2* information by changing parameters.

To produce the echo, a gradient echo pulse sequence uses

a gradient magnetic field only

When a sudden loss in temperature occurs which causes the coils to no longer be superconducting, resulting in helium escaping from the cryogenic bath is termed:

a quench

How would you best describe EPI (echo planar imaging) sequences?

a train of gradient echoes

Describe FSE

a train of spin echoes

Artifact that occurs in the phase direction and is caused by anatomy outside the FOV. Is under sampled, causing a misregistration, resulting in what is commonly called wrap around is what type of artifact?

aliasing

During transport of the patient, the urinary collection bag should be placed

below the bladder

The ______ valve lies between the left atrium and left ventricle

bicuspid / mitral

What three branches come off the aorta?

brachiocephalic, left subclavian, left carotid

The first major branch of the abdominal aorta is the:

celiac trunk

As the number of phase encodings increase from 250 to 500, the SNR will _______

decrease (less protons per voxel)

Reducing the FOV will result in

decreased SNR

Reducing the TE results in images with what change in contrast?

decreased T2 information

Reducing the number of lines filled in K space will produce an image with:

decreased spatial resolution increased SNR Decreased scan time

This is describe as movement of molecules in the extra cellular space

diffusion imaging

To best visualize the anterior cruciate ligament on knee MR

externally rotate the leg about 15

To minimize CSF flow artifacts on a cervical spine, what type of sequence could be used?

gradient moment nulling

The liquid cryogen (s) commonly used to maintain the primary magnet coil at superconducting temperature is / are

helium

What element in the body is the principle nucleus used in MR?

hydrogen

A major advantage of a 2D time of flight sequence over a 3D time of flight is the ability to

image a larger area without saturation of the flowing blood.

Interventional MRI is used for.

imaging skeletal muscle injuries

A gradient echo sequence in which all the remaining residual transverse magnetization is removed prior to the next excitation pulse is

incoherent/spoiled

Which will lengthen scan time in a pulse sequence:

increase TR decrease echo train length increase NEX decrease parallel imaging factor

The time during which the frequency encoding gradient is on __________________ a reduction in receiver bandwidth

increases with

A complication or illness caused by the treatment from a healthcare professional is termed

latrogenic

The largest ventricle in the heart

left ventricle

Water has a ______ T1 relaxation time and a _______ T2 relaxation time

long / long

Force of an object in a magnetic environment depends on the following:

mass of the object, strength of the magnet, ferromagnetic properties of the object

In complete spine imaging, to rule out metastatic lesions of the spinal cord, contrast enhancement can be used with T1 weighted images because

metastatic lesions enhance and normal cord does not

When triggering a scan from the patient's EKG, the TR of the sequence is determined by the

patient's heart rate

When using bright blood MRA to evaluate peripheral vascular flow, such as that within the arteries of the legs, saturation pulses are

placed inferior to the acquired slices

In a medical malpractice lawsuit, the ____ must be able to prove medical malpractice

plaintiff / patient

The presaturation pulses usually occur

prior to the excitation pulse

Which veins transport oxygenated blood?

pulmonary

The type of RF coil configuration that uses a pair of coils perpendicular to each other to transmit and receive signal is known as a ______________________ coil.

quadrature

Reducing scan time can be achieved by:

reducing TR reducing NEX using half fourier using a course matrix increased parallel imaging factor

When scanning a patient with chiari malformation, which would be the best imaging plane?

saggital

In a time of flight sequence, the tissue is hypointense relative to flowing blood because of

saturation effects

Fat has a ______ T1 relaxation time and a ______ T2 relaxation time

short / short

The removal of signal from vessels in an MRA sequence is achieved by

spatial presaturation

The transmit bandwidth of the RF pulse effects:

spatial resolution, SNR, slice thickness

If the TR of a gradient echo pulse sequence is considerably less than the T2 (and T2*), the condition that will exist is known as

steady state

To visualize arterial flow during an MRA study of arterial flow, where should pre-saturation pulse be applied to remove signal from venous flow?

superior to the slice stack

Which coil has a characteristic drop off of signal beyond the physical edge of the coil?

surface

In a spin echo sequence, flowing blood is normally seen as a signal void because

the 90o pulse and the 180o pulse are both slice selective

The gradient slew rate is:

the rate of speed of descent to ascent of a gradient from zero to maximum

Which of the following has been documented to cause muscle contractions, alterations in vision and biochemistry of cells?

time varying magnetic fields

Which valve lies between the right atrium and right ventricle?

tricuspid

How does a double IR prep sequence begin

two 180 degree RF pulses

To avoid the "magic angle" (an artifactual brightness seen in the medial segment of the posterior horn of the lateral meniscus when short TEs are used) artifact when imaging the knee,

use a longer TE, reposition the knee, orient the affected anatomy to another angle

Due to the differences in frequencies across the magnetic field we

use gradients, use sat bands, . use different coils

Diseases, such as Malaria, in which microorganisms are transferred via an insect are classified as

vector borne

Phase contrast techniques produce image in which the signal intensity within the vessel is dependent on (among other parameters) the

velocity of the flowing blood

A major advantage of 3D time of flight techniques over 2D time of flight is the ability to

visualize smaller vessels

T2 weighted FLAIR are typically used for evaluation of what?

white matter diseases