Curve fit tab

Sequence specifications tab

Sequence specification:

Sequence type:

Available options: Inversion Recovery (IR), Saturation Recovery (SR) or multiple flip angle spoiled gradient echo (SPGR)

For IR type, subtypes can be Modulus or Real:

Modulus curve:

Negative values on the IR curve are represented as the modulus value.

Real curve:

negative pixel values are allowed

If sequence type is set to either SR or IR then multiple sequence related options can be set in the IR sequence option panel:

Apply Look-Locker correction:

Corrects the calculated T1/R1 values for the effect of signal saturation in Look-Locker type sequences (multiple RF excitation pulses after a single inversion pulse). The flip angle must be specified when this option is enabled, and the option is only valid for IR curves.

Correct for imperfect inversion pulse:

When T1 is estimated from an Inversion Recovery (IR) sequence, the formula used is: SI(TI) = A[1- B exp(-TI/T1)] where TI is the inversion time, A is a constant reflecting equilibrium magnetization and B is a value reflecting the magnitude of the inversion (180 deg) pulse. For a 'perfect' IR sequence B=2, but the value may deviate from 2 when the B1-excitation field is imperfect, causing the value of B to vary across the field of view. When this option is enabled, the parameter B is allowed to vary (i.e. included as a parameter to be fitted). This will account for variations in the inversion pulse, but also increases the number of degrees of freedom in the fitting procedure, which can result in greater variation in the resulting R1/T1 estimation. Note that when the option 'Apply Look-Locker correction' is enabled, correction for imperfect inversion pulse is always applied, since this is part of the Look-Locker correction algorithm.

Baseline offset: When enabled, an offset parameter is added to the model expression to account for the fact that the signal level never reaches zero for modulus IR curves (due to image noise). This option is not used for SR images of for real IR data

Inversion/Saturation time (TI/TD) Parameters:

Constant TI/TD spacing: Selected if a constant inversion or delay time spacing is used. Min TI/TD is the time of the first inversion/saturation time and Delta TI/TD is the spacing of successive time-points after the first TI/TD time. All times are in msec.

Edit TI/TD values: The inversion- or delay times are specified in a list. This would be used in situations where the TI/TD values are sampled at uneven intervals (and not specified in the DICOM header).

Ignore Dicom values: If TI values are present in the DICOM header, but one wishes to use other values.

Multiple flip-angle SPGR sequence parameters:

Constant flip angle increment/decrement: Selected if a constant flip angle increment or decrement is used. First FA is the flip angle of the first image and FA increment/decrement is the constant change in flip angle for each consecutive image in the series. All values are in degrees.

Edit flip angles: The flip angles used are specified in a list. This would be used in situations where a non-constant flip angle increment or decrement is used (and the values are not specified in the DICOM header).

Sequence specifications tab

Multiple flip-angle SPGR sequence parameters:

Constant flip angle increment/decrement: Selected if a constant flip angle increment or decrement is used. First FA is the flip angle of the first image and FA increment/decrement is the constant change in flip angle for each consecutive image in the series. All values are in degrees.

Edit flip angles: The flip angles used are specified in a list. This would be used in situations where a non-constant flip angle increment or decrement is used (and the values are not specified in the DICOM header).

Repetition time: Specifies the repetition time (TR) of the SPGR sequence

Ignore Dicom values: If valid flip angles and TR values are present in the DICOM header, but one wishes to use other values.

Related topics: