Mixed Deck — All MRI Topics Flashcards

Which MRI technique encodes functional brain activity by detecting changes in blood oxygenation level?

Answer: Blood oxygen level-dependent (BOLD) fMRI

BOLD fMRI detects regional neural activity via the magnetic susceptibility difference between oxyhemoglobin and deoxyhemoglobin, providing maps of brain activation.

Which of the following precautions is required before administering a GBCA to a breastfeeding mother, according to ACR recommendations?

Answer: No precautions are required as only trace amounts enter breast milk

The ACR states that GBCAs enter breast milk in very small amounts (<0.04%) and oral bioavailability is negligible; no interruption is required, though the mother may choose to withhold for 12–24 hours if concerned.

Which parameter in MRI controls the field of view (FOV) and therefore directly affects spatial resolution when matrix size is held constant?

Answer: FOV size relative to matrix (voxel size = FOV/matrix)

Voxel size = FOV divided by matrix; decreasing FOV while maintaining matrix size decreases voxel size, increasing spatial resolution but reducing SNR.

Which MRI sequence is most commonly used for evaluating liver lesions using T2 contrast with heavy T2 weighting for the bile ducts?

Answer: MRCP (heavily T2-weighted 3D or thick-slab)

MRCP uses heavily T2-weighted sequences to make bile and pancreatic fluid appear bright, providing a non-invasive map of the biliary and pancreatic ductal system.

Inversion recovery sequences null a specific tissue when the readout pulse is applied at time TI equal to:

Answer: 0.693 × T1 of the tissue (T1 × ln2)

The longitudinal magnetization of a tissue crosses zero at TI = T1 × ln(2) ≈ 0.693 × T1; applying the readout at this moment nulls that tissue's signal.

Which coil type generally provides the highest SNR for imaging a small superficial structure?

Answer: Surface coil

Surface coils placed close to the target anatomy have superior SNR for small or superficial structures because they detect signal from a limited volume with less noise.

For MRI of the shoulder, the patient should be positioned with the arm in which orientation to best center the glenohumeral joint?

Answer: Arm at the side in neutral or slight external rotation, shoulder centered in the coil

Positioning the shoulder with the arm at the side in neutral or slight external rotation and centering the glenohumeral joint within the dedicated shoulder coil optimizes image quality.

What is the recommended action when a patient with an unknown metallic implant cannot be identified before a clinically urgent MRI?

Answer: Consult the radiologist and ordering physician to assess risk vs. benefit

The radiologist and referring physician must jointly assess whether clinical urgency outweighs the unquantified risk of scanning with an unknown implant.

What happens to image contrast when the echo time (TE) is increased in a T2-weighted sequence?

Answer: T2 contrast increases as tissues with short T2 decay faster

Longer TE allows more T2 decay to occur, so tissues with short T2 lose signal faster and appear darker, enhancing T2 contrast between tissues.

Nephrogenic Systemic Fibrosis (NSF) is a serious complication associated with GBCA administration in patients with:

Answer: Severe renal impairment (GFR <30 mL/min/1.73m²)

NSF occurs almost exclusively in patients with severe kidney disease (GFR <30) because impaired renal clearance prolongs gadolinium exposure, allowing transmetallation and tissue deposition.

Which coil type provides the highest signal-to-noise ratio (SNR) for imaging small superficial structures such as the wrist?

Answer: Dedicated extremity or surface coil

Dedicated extremity or surface coils placed close to the anatomy maximize SNR by minimizing the receive volume to the region of interest.

In MRI, the term 'flip angle' refers to:

Answer: The angle by which the net magnetization is rotated from B0 by the RF pulse

The flip angle is the degree of rotation of the net magnetization vector away from the longitudinal axis produced by an RF pulse.

In diffusion-weighted imaging (DWI), a high b-value results in:

Answer: Greater diffusion weighting and lower overall signal

Higher b-values apply stronger diffusion-sensitizing gradients, so freely diffusing water loses more signal, increasing lesion conspicuity for restricted diffusion.

What is the preferred patient position and coil for imaging the rotator cuff of the shoulder?

Answer: Supine, arm at side in neutral rotation, dedicated shoulder coil

Supine positioning with the arm at the side in neutral rotation and a dedicated shoulder coil provides optimal SNR and comfort for rotator cuff imaging.

The ARRT MRI registry exam content specification places approximately what percentage of questions in the 'Procedures' domain?

Answer: 35%

Approximately 35% of the MRI registry exam covers Procedures, making it one of the largest content areas.

What is the effect of increasing receiver bandwidth on MRI image quality?

Answer: SNR decreases but chemical shift artifact is reduced

Increasing bandwidth reduces chemical shift artifact and allows shorter TE/TR, but more noise is accepted per unit time, lowering SNR.

Require the employment of solenoid coils because of the B0's orientation; these coils are more effective than linear coils and can be electrically combined with other coils to enhance signal homogeneity across an area of interest.

Answer: Vertical

Vertical coils are specifically designed for MRI systems where the main magnetic field (B0) is oriented vertically, often found in open or permanent magnet systems. These coils are more effective than linear coils in this orientation and can be electrically combined with other coils to enhance signal homogeneity across the area of interest, optimizing signal reception for vertical field systems.

Magnets formed of ferrous material found naturally or from blocks or slabs.

Answer: Permanent

Permanent magnets are created from naturally occurring ferromagnetic materials or specially treated blocks of ferrous material. These magnets retain their magnetism without requiring an external power source. They produce a constant magnetic field and are typically utilized in low-field MRI systems, offering a simpler and less costly design.

Which MRI technique measures cerebral blood flow and volume without contrast injection, using arterial water protons as an endogenous tracer?

Answer: Arterial spin labeling (ASL)

ASL uses RF pulses to magnetically label (invert) arterial blood water protons proximal to the imaging slab; labeled images are subtracted from control images to quantify cerebral perfusion.

Traditional GRE order

Answer: Reduce the impact of residual transverse magnetization by using spoiler gradients.

In traditional (spoiled) Gradient Echo (GRE) sequences, spoiler gradients are applied at the end of each TR period. The primary purpose of these gradients is to intentionally dephase any residual transverse magnetization. This prevents the magnetization from contributing to the signal in subsequent TRs, ensuring that the signal primarily reflects T1 weighting and maintains consistent image contrast by avoiding contamination from previous excitations.