Table 1.

Comparison of RC-4DMRI, 2D/3D cine MR, TR-4DMRI with 4DCT and 2D kV/MV.

Category	Sub-category	4DCT	RC-4DMRI	2DkV/MV	2D cine	3D cine	TR-4DMRI
Acquisition	Scanning	Projection	2D slice	Projection	2D slice	3D volume	3D
	Moving Couch	Yes	No	No	No	No	No
	Ionizing Radiation	Yes	No	Yes	No	No	No
	Preferred Scan Directions∧	Axi	Axi/Sag/Cor	Obl/Sag/Cor	Obl/Sag/Cor	Sag/Cor	Sag/Cor
	3D Recon#	FBP	iFFT	NA	NA	iFFT	iFFT
	4D Recon#	Binning	Binning	NA	NA	NA	SR
Contrast	Lung&	High	High (T2)	Low	Mid	Mid	High (T2)
	Abdomen&	Low	High	Low	High	High	High
Motion	Respiratory Surrogate	External	Internal (/External)	NA	NA	NA	NA
	Cyclical Motion Assumption	Yes	Yes	No	No	No	No
	Binning Artifacts$	High	Low	No	No	No	No
	Multi-breathing Cycles	No	No	Yes	Yes	Yes	Yes

^∧Preferred scan directions include Axial (Axi), Sagittal (Sag), Coronal (Cor), and oblique (Obl). The coronal scan is often used in 3D cine due to shorter anterior-posterior separation of the human body.

^#Reconstruction methods using the filtered back project (FBP), inverse fast Fourier transform (iFFT), and super-resolution (SR) methods.

^&T1 or balanced steady-state free-precession (bSSFP) MR contrasts are used for real-time scan.

^$High binning artifacts for irregular breathers in 4DCT. Low binning artifacts in RC-4DMRI when using an internal navigator with the Cartesian acquisition and No binning artifacts when using self-navigator in the Golden-angle radial acquisition.