Table 1 Standard pulse sequence parameters and protocol setting for magnetic resonance myocardial T1ρ mapping at 1.5-T

Acquisition

(2D) Single-shot SSFP

(3D) SPGR

Allows for rapid 2D image acquisition that is robust to motion, especially in arrhythmic patients or poor breath-holders

Cardiac control

ECG triggering

Usually performed in mid-diastole to minimize the effects of cardiac motion

Respiratory control

(2D) Breath-holding

(3D) Free-breathing navigated

Non-rigid motion correction is recommended even under breath-holding [42, 59, 80]

Spatial resolution

1.4 × 1.4 mm² to 1.7 × 1.7 mm²

Balance the image resolution and the amount of expected cardiac motion

Slice thickness

8–10 mm

Can be reduced for 3D acquisitions

Acquisition window

160–250 ms

For 3D imaging, increasing the data acquisition window will reduce scan time but will increase cardiac motion

Bandwidth

900 Hz/pixel

–

Flip angle

70º

Single-shot imaging with a flip angle of 70º was shown to achieve low mean T1ρ bias in phantom experiments [59]

Recovery heartbeats

3

To allow for sufficient T1 recovery when no saturation pulses are incorporated in the sequence. This could also be countered with dictionary matching

Acceleration

(2D) GRAPPA R = 2 with 34 reference lines

(3D) Variable density trajectory R = 3–4 [52, 55]

Increased acceleration (higher R) will reduce scan time (3D) or acquisition window duration but may also affect image quality. In 3D, advanced undersampling and reconstruction strategies may allow high acceleration (R = 3–4) [52, 55]

T1ρ number

5–7 (durations = 0 to 55 ms)

The optimal number of pulses and corresponding spin-lock durations still have to be optimized (resorting to Cramér-Rao Lower Bound for example [72])

T1ρ durations

0, 10, 20, 35, 50 ms

Spin-lock frequency

400 Hz (B1 amplitude: 9.4 μT)–500 Hz (11.7 μT)

To stay within the allowed specific absorption rate limits

T1ρ module

\({90}_{x}-S{L}_{-y}-{180}_{-y}-S{L}_{-y}-{90}_{-x}\)

This module inserts a 180º refocusing pulse between the two spin-lock segments and was shown to be insensitive to B0 and B1 inhomogeneities [3]. A thorough analysis of all existing T1ρ modules remains to be performed

Acquisition time

Spin-lock number \(\times\) Recovery heartbeats

In practice, single-shot 2D acquisitions require a breath-hold per slice. Depending on the resolution, the motion correction technique, and the sampling acceleration strategy, 3D T1ρ maps can be acquired in less than 10 min