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MRI Math

MRI Math Equations

QuestionAnswer
Scan time: Spin Echo TR x Phase Matrix x NSA/NEX = Scan Time
ms (milliseconds) into seconds Divide by 1000
Scan time: Fast Spin Echo Fast Spin Echo Sequence : TR x Phase Matrix x NEX ÷ ETL
Scan time: 3D Gradient Echo TR x Phase Matrix x NSA/NEX x # Slices = 3D Scan Time
Pixel Size FOV ÷ Matrix = pixel size
Pixel Size Dimensions (phase and frequency) FOV ÷ phase matrix = phase dimension pixel FOV ÷ frequency matrix = frequency pixel
Pixel Area Multiply phase pixel size x frequency pixel size = Pixel area (answer squared^2)
Voxel volume Pixel area x slice thickness = Voxel volume (answer cubic^3)
NSA/NEX and SNR SNR increase calculated by the square root (√) of the increase
Bandwidth and SNR Decreasing BW by factor of 2 increases SNR by √2
FOV and SNR Reducing the FOV decreases SNR by a factor of the FOV^2
Example of FOV and SNR Reducing the FOV from 40cm to 20cm results in SNR reduced to ¼ the original SNR, due to the voxel volume being reduced by a factor of 4
Calculate effective TR 60,000 ÷ heart rate (60 seconds per minute, 1000 milliseconds per second)
Calculate available imaging time in a Cardiac MR Effective TR – (delay and trigger window)
Example of imaging time in Cardiac MRI For example, Heart Rate 80bpm, Trigger delay 50ms, Trigger window 10%, what is the available imaging time? 60000 ÷ 80 = 750ms. 750 – 125 (75{10% of 750} + 50{delay}=125) = 625 ms total available imaging time
How to convert lbs to kg divide by 2.2
Calculating Contrast dose? dose (mmol/kg) x weight (kg) ÷ concentration (mmol/ml)
Created by: emjohnson4
 

 



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