Utility of Navigator-Prospective Acquisition Correction Technique (PACE) for Reducing Motion in Brain MR Imaging Studies

American Journal of Neuroradiology

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Fig 1.
The navigator box is positioned midsagittal just posterior to the bregma.
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Fig 2.
A, Sagittal T1 FSE (TR, 429 ms; TE, 10 ms; acquisition time, 2 minutes) demonstrates considerable motion artifacts in our patients undergoing mechanical ventilation.
B, Sagittal T1 FSE (TR, 429 ms; TE, 10 ms) with the navigator pulse to gate the same as patient's head rocking motion. Although the acquisition time for this sequence was 3.5 minutes, it is still far superior in quality to the original FSE (A).
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Fig 3.
A, Axial T2 FSE (TR, 5890 ms; TE, 104 ms; echo train, 21; acquisition time, 2 minutes) performed without gating and resulting in a nondiagnostic image due to head rocking secondary to high-pressure ventilation.
B, Axial T2 FSE (TR, 6635 ms; TE, 89 ms; echo train, 21; acquisition time, 5 min). This is the same sequence and patient seen in A but with the addition of the navigator pulse.

Table 1:

Sequences run on patient 1

	Acquisition Time (min:sec)	TR (ms)	TE (ms)	Echo Train	Resolution	IPAT Acceleration Factor	Comments
T1 SAG FSE	2:08	429	10	3	256 × 205	2	Nondiagnostic due to motion
T2 Ax FSE	2:22	5890	104	21	256 × 205	2	Nondiagnostic due to motion
T1 GRE, 3 planes	0:32	102	4.8	NA	256 × 156	2	Nondiagnostic due to motion
T1 FSE with navigator, 3 planes	3:30–4:00	429	10	3	256 × 205	2	Diagnostic
T2 Ax FSE	3:00	5890	104	21	256 × 205	2	Nondiagnostic
T2 Ax FSE navigator	5:00	6635	89	21	256 × 205	2	Diagnostic

Note:—IPAT indicates integrated parallel acquisition technique; SAG, sagittal; FSE, fast spin-echo; Ax, axial; GRE, gradient-echo; NA, not applicable. Both the TR and the acquisition time will be a variable of the frequency of patient motion. They should be adjusted inversely with concatenations to keep the effective TR short for T1 sequences.

Table 2:

Sequences run on patient 2

	Acquisition Time (min:sec)	TR (ms)	TE (ms)	Echo Train	Resolution	IPAT AccelerationFactor	Comments
T1 SAG and Cor FSE	2:18	475	16	3	256 × 256	2	Nondiagnostic due to motion
T2 Ax FSE	2:22	5890	104	21	256 × 205	2	Nondiagnostic due to motion
T1 GRE, 3 planes	0:32	102	4.8	NA	256 × 156	2	Nondiagnostic due to motion
T1 FSE with navigator, 3 planes	4:00–6:00	429	10	3	256 × 205	2	Diagnostic
T2 Ax FSE	4:30	5890	104	21	256 × 205	2	Diagnostic

Note:—IPAT indicates integrated parallel acquisition technique; SAG, sagittal; Cor, coronal; FSE, fast spin-echo; Ax, axial; GRE, gradient-echo; NA, not applicable. Both the TR and the acquisition time will be a variable of the frequency of patient motion. They should be adjusted inversely with concatenations to keep the effective TR short for T1 sequences.