Room: Exhibit Hall | Forum 8
Purpose: Accuracy of T1w signal and change in resolution in k-space substitution (e.g. Keyhole imaging) can be evaluated using ADNI phantom. Aims: (i) compare T1w phantom signal error fluctuation as k-space substitution increases (ii) investigate how k-space change the noise level and (iii) investigate to what extent spatial resolution is affected.
Methods: An ADNI phantom (EMR051, MagphanÂ®, containing eight T1 inserts) was placed in the head coil of 3T Siemens TIM Trio MRI system. Two sets (n=4) of T1W-MPRAGE images were collected using different inversion times (TI=1500,930,1500,1100 ms respectively) with TR=3.6s, bandwidth=180kHz, no acceleration and flip angle=6. Keyhole technique was applied in phase encoding (PE) direction and frequency (FE) encoding direction to generate different percentage of k-space substitution. FFT and sum of square were applied to generate coil-combined magnitude images. Precision error of the eight T1W phantoms signals, and noise profiles were evaluated with varying percentage k-space substitution. Spatial limiting resolution was evaluated using modulation transfer function. Consistency of measurement errors was evaluated using the standard error of mean (SEM).
Results: The signal errors started to be consistently low for 60 lines replaced in PE direction (0.8%,SEM 0.1% and lower thereafter), and for 100 lines in FE direction (1.3%, SEM 0.4%, and lower thereafter, Figure 1). Substitution in FE direction gives higher T1W signal error than in PE direction (5.3Â±14.2% vs 1.7Â±4.2% group mean/SD), while with lower noise(159.6Â±33 vs 197.1Â±89). Limiting resolution varies from 0.294â€“0.282 for PE (3.4% in variance), and 0.268-0.254 for FE (8% in variance) with different substitutions.
Conclusion: T1 error is consistently low with 60/256 or more of k-space replaced in PE direction, while more varying errors are found in FE directions. Fluctuations in spatial resolution and noise also were identified, but at an acceptable range.
Not Applicable / None Entered.