MRI Parameters

Headers of chart

Parameter, SNR, Scan Time, Detail, SAR, Other

Increased TR

SNR up, scan time up, detail unchanged, SAR down, T1 contrast down, number of slices up

Increased TE

SNR down, scan time up, detail unchanged, SAR unchanged, T2 weighting up, number of slices down

TR

Repetition time- time between RF pulses

TE

Echo time- time between start of RF pulse and peak of signal echo received

SNR

Signal to noise ratio

SAR

Specific absorption rate- the rate the tissue absorbs RF energy ; heat

NSA

Number of Signal Averages (also NEX) - number of times a line is sampled for improved image clarity.

NEX

Number of Excitations (also NSA) - number of times a line is sampled for improved image clarity.

Increased FOV

Increased signal, time unchanged, decreased detail, SAR unchanged, more coverage

Increased NSA

Increased signal, increased time, detail unchanged, increased SAR, risk of movement increased

Increased ETL

Decreased signal, decreased time, detail unchanged, increased SAR, more blur

ETL

Echo train length

What effect does increased ETL have on scan time

Increased ETL decreases scan tone because it collects multiple lines of data after a single pulse