A free induction decay (FID) signal can only occur after a 90 degree pulse

After a 90 degree pulse, the longitudinal magnetization recovers at the same rate as the

transverse magnetization decays

The rate of the longitudinal magnetization recovery does not depend on the external

magnetic field strength

Dephasing of the transverse magnetization is mainly due to spin–spin relaxation

The FID is not usually considered in clinical MRI

Signal is generated from 12C nuclei

Paramagnetic contrast agent is used to enhance tissue contrast

The SI unit for main magnetic field strength is Gauss

Scanning time is reduced by using shorter time to repeat (TR)

Vascular pulsation artefacts occur in the phase encoding direction

Larmor frequency is proportional to the proton density

the flip angle depends on the applied radiofrequency strength

the free induction decay signals are detected with gradient coils

nuclei with odd number of nucleons are used

the longitudinal magnetization lies perpendicular to the X-Y plane

The first radiofrequency pulse in a spin–echo pulse sequence is a 180 degree pulse

Rephasing of the transverse magnetization is caused by the 180 degree pulse

Effects of local field inhomogeneities on the MRI signal are eliminated

For practical purposes, the delay between excitation and the refocusing pulse is kept constant, but signal readout can be performed at any chosen echo time (TE)

Rephasing can only be performed once, and the whole sequence must be repeated to obtain another echo

increasing TR will decrease the signal intensity on T2-weighted

decreasing pixel size will decrease signal-to-noise ratio

image resolution is improved by increasing the matrix size

shimming improves field homogeneity

image quality is unaffected by TE (echo time)

TR is the time between two 90 degree radiofrequency pulses

Signal read-out during the 180 radiofrequency pulse

Field inhomogeneity is due to introduction of patient onto the magnetic field.

Spin-Spin relaxation is T1 relaxation.

T2 is the time for the MR signal to fall to 63% of its maximum value.

The best contrast between tissues with different T1s is obtained with short repetition times (TRs) and short echo times (TEs)

T2 weighting is obtained with short TEs and long TRs

An image obtained with a TE of 15 ms and a TR of 2000 ms would be proton density (PD) weighted

Fat appears with a high signal on T1-, T2- and PD-weighted sequences

The fat signal is partially suppressed on fast (turbo) spin–echo imaging

The slice-selection gradient is usually applied just before the 90 degree and 180 degree radiofrequency (RF) pulses

A phase-encoding gradient is usually applied along the larger dimension of the imaged object

The entire phase-encoded information is obtained during a single readout

A frequency-encoding gradient is applied together with the phase-encoding gradient

A spin–echo sequence requires a rephasing gradient applied after the slice-selection gradient

1. Tissue with higher proportion of free water has longer T2 relaxation time

1. Lamour frequency is inversely proportional to strength of external magnetic field.

1. The central area of K space represent contrast of image

1. Chemical shift artefact can be reduced by increasing receiver bandwidth

1. Higher gradient amplitude increase the slice thickness

It is most commonly used with gradient-echo sequences

In a 1.5 T magnet, the magnetization of fat and water becomes out of phase every 220 ms

A gradient echo obtained with a TE of 6.9 ms at 1.5 T would represent a summation of signals from fat and water

The most common application of out-of-phase imaging is in the diagnosis of hepatic and adrenal lesions

Out-of-phase images show a characteristic ‘India ink’ appearance

It can be used to achieve T1 weighting or to suppress the signal from a specific tissue type

The inversion recovery sequence starts with a 90 degree excitation pulse

In short-TI inversion recovery (STIR) imaging, the TI is set equal to the T1 of fat so that the signal from fat is nulled

Image acquisition in FLAIR is usually combined with a T2-weighted spin–echo sequence

Inversion recovery sequences require high field magnets and are sensitive to magnetic field inhomogeneities

The main advantage of short-TI inversion recovery (STIR) as a method of fat suppression is its specificity

Out-of-phase imaging alone is useful for suppressing signal from adipose tissue

Frequency-selective fat saturation is achieved by applying a chemical shift-selective excitation pulse followed by a spoiler gradient

Higher magnetic field strengths allow better spectral fat saturation

The signal-to-noise ratio (SNR) in images obtained with spectral fat saturation is worse in comparison with STIR

Motion artefacts occur mainly in the frequency-encoding direction

Aliasing usually occurs in the phase-encoding direction of 2D images

Magnetic susceptibility effects are more pronounced on spin–echo than on gradient-echo sequences

Chemical-shift artefacts are virtually eliminated in 3 T scanners

Ringing (Gibbs) artefacts can be eliminated by increasing the matrix size

Balanced steady state free precession (BSSFP) reduces CSF pulsation artifact.

CT myelogram is acquired 4H post injection.

Maximum age for ultrasound is 2 months.

RAO view of lumbosacral spine demonstrates pars interarticularis.

Spinal DSA is the first line study to diagnose spinal vascular anomaly.