schemes

schemes ¶

ASL labeling scheme definitions and parameters.

This module defines the parameters for different ASL labeling schemes per the OSIPI ASL Lexicon terminology:

PASL (Pulsed ASL) -- labeling efficiency (alpha), inversion time (TI) in ms
CASL (Continuous ASL) -- labeling duration (tau/LD) in ms, PLD in ms
pCASL (pseudo-Continuous ASL) -- labeling duration (tau/LD) in ms, PLD in ms

References

.. [1] OSIPI ASL Lexicon, https://osipi.github.io/ASL-Lexicon/ .. [2] Alsop DC et al. (2015). Recommended implementation of arterial spin-labeled perfusion MRI for clinical applications. Magn Reson Med 73(1):102-116. .. [3] Dai W et al. (2008). Continuous flow-driven inversion for arterial spin labeling using pulsed radio frequency and gradient fields. Magn Reson Med 60(6):1488-1497.

LabelingScheme ¶

Bases: Enum

Enumeration of ASL labeling schemes.

PASLParams `dataclass` ¶

PASLParams(
    ti=1800.0,
    ti1=700.0,
    bolus_duration=700.0,
    labeling_efficiency=0.98,
    inversion_flip_angle=180.0,
)

Parameters for Pulsed ASL (PASL).

ATTRIBUTE	DESCRIPTION
`ti`	Inversion time (TI) in milliseconds. Time from labeling pulse to image acquisition. TYPE: `float`
`ti1`	First TI for QUIPSS II or Q2TIPS (ms). Time at which saturation pulse is applied. TYPE: `float \| None`
`bolus_duration`	Bolus duration (τ) in milliseconds. Effective labeling duration. TYPE: `float`
`labeling_efficiency`	Labeling efficiency (α), typically 0.95-0.98 for PASL. TYPE: `float`
`inversion_flip_angle`	Flip angle of inversion pulse in degrees. TYPE: `float`

CASLParams `dataclass` ¶

CASLParams(
    label_duration=1800.0,
    pld=1800.0,
    labeling_efficiency=0.71,
    rf_power=3.0,
    gradient_amplitude=10.0,
)

Parameters for Continuous ASL (CASL).

ATTRIBUTE	DESCRIPTION
`label_duration`	Duration of labeling RF pulse (τ) in milliseconds. TYPE: `float`
`pld`	Post-labeling delay (PLD) in milliseconds. TYPE: `float`
`labeling_efficiency`	Labeling efficiency (α), typically 0.68-0.73 for CASL. TYPE: `float`
`rf_power`	RF power during labeling in μT. TYPE: `float`
`gradient_amplitude`	Labeling gradient amplitude in mT/m. TYPE: `float`

PCASLParams `dataclass` ¶

PCASLParams(
    label_duration=1800.0,
    pld=1800.0,
    labeling_efficiency=0.85,
    average_b1=1.5,
    average_gradient=0.5,
    pulse_duration=500.0,
    pulse_gap=500.0,
    num_pulses=None,
)

Parameters for pseudo-Continuous ASL (pCASL).

pCASL is the recommended labeling scheme per ISMRM consensus.

ATTRIBUTE	DESCRIPTION
`label_duration`	Duration of labeling train (τ) in milliseconds. TYPE: `float`
`pld`	Post-labeling delay in milliseconds. TYPE: `float`
`labeling_efficiency`	Labeling efficiency (α), typically 0.85-0.95 for pCASL. TYPE: `float`
`average_b1`	Average B1 during labeling in μT. TYPE: `float`
`average_gradient`	Average gradient during labeling in mT/m. TYPE: `float`
`pulse_duration`	Duration of each RF pulse in microseconds. TYPE: `float`
`pulse_gap`	Gap between RF pulses in microseconds. TYPE: `float`
`num_pulses`	Number of RF pulses in labeling train. TYPE: `int \| None`

compute_labeling_efficiency ¶

compute_labeling_efficiency(
    scheme, params=None, measured_efficiency=None
)

Compute or return labeling efficiency.

PARAMETER	DESCRIPTION
`scheme`	Labeling scheme type. TYPE: `LabelingScheme`
`params`	Labeling parameters. TYPE: `PASLParams \| CASLParams \| PCASLParams \| None` DEFAULT: `None`
`measured_efficiency`	If provided, use this measured value instead of default. TYPE: `float \| None` DEFAULT: `None`

RETURNS	DESCRIPTION
`float`	Labeling efficiency (0 to 1).

Notes

Default efficiencies per ISMRM consensus (Alsop et al., 2015): - PASL: 0.98 - CASL: 0.71 - pCASL: 0.85