***Transition Times based on vessels that are clear of pathology and are lying within normal tissue.
7
Average Arrival Times of Contrast in ceMRA
8
Vessel Superior Vena Cava
Arrival Time 0-8 seconds
Pulmonary Artery
6-10 seconds
Carotid Artery
7-12 seconds
Aortic Arch
9-14 seconds
Descending Aorta
13-20 seconds
Femoral Artery
15-20 seconds
Hepatic Artery
19-30 seconds
Trifurcation
20-30 seconds
Palmer Arch
20-40 seconds
Portal Veins
30-45 seconds
Hepatic Veins
40-55 seconds
***Arrival times based on normal, pathology-free, anatomy.
MRI Formulas
SNR
Mean of Tissue/Standard Deviation = Signal to Noise Ratio
Place a small ROI within the tissue to establish the Mean Value. A large ROI in the background will determine the Standard Deviation.
Bandwidth Conversion (Hz/Px to kHz) In-Plane Pixel (phase) In-Plane Pixel (frequency) SNR Improvement Voltage Improvement Inversion Time Calculation
(Hz per Pixel/Base Resolution) / 2000 = kHz EXAMPLE: 130 hz/px X 256 (freq.) = 33,333 33,333/2000 = 16.021 kHz
FOVp/Np FOVp - FOV in the Phase Direction NP - Number of Phase Encoding Steps
FOVf/Nf FOVf - FOV in the Frequency Direction Nf - Number of Frequency Encoding Steps
(SNR 1 - SNR 2)/SNR 2 x 100 = % of Improvement Comparison of SNR between two sequences; establish an SNR for each sequence and plug the values into the above formula. Positive results indicate SNR1>SNR2. Negative results reflect SNR1