Normal and Variant Abdominal Anatomy on Magnetic Resonance Imaging

The diagnostic usefulness of abdominal magnetic resonance (MR) imaging lies in the improved contrast resolution and ability to qualify several tissue characteristics of a specific organ or lesion. Our institution uses organ-specific protocols to facilitate technical reproducibility and optimize scan duration. These protocols are discussed individually in this article when applicable, noting that many build on a basic protocol with slight variations. Because most abdominal MR imaging studies are targeted toward an organ or area of interest, this article discusses the protocol strategies and relevant anatomy in a segmented/organ-specific manner.

Abdominal magnetic resonance (MR) imaging has traditionally been used as a problem-solving method after a previous indeterminate imaging investigation such as computed tomography (CT) or ultrasound, frequently using organ-specific protocols to highlight the condition in question. Increasingly, abdominal MR imaging is being used as a primary imaging investigation with expansion of clinical indications and increased awareness of cumulative ionizing radiation dose in medical imaging. Therefore, it is important to understand the normal abdominal anatomy on MR imaging, particularly the visceral organ appearances, as well as commonly encountered variants and disease mimics. Because most abdominal MR imaging studies are targeted toward an organ or area of interest, this article discusses the protocol strategies and relevant anatomy in a segmented/organ-specific manner.

In general, abdominal MR imaging benefits substantially from the use of a high field strength magnet (1.5 Tesla or greater) and local phased-array surface coils around the anatomy of interest. Most commonly, breath-held sequences with high temporal resolution and moderate spatial resolution are frequently used in abdominal MR imaging to mitigate the effects of respiratory and bowel motion. However, when high spatial resolution and improved image signal are required, motion compensation techniques such as respiratory triggering or diaphragm-navigation can be used to facilitate longer acquisition times. The diagnostic usefulness of abdominal MR imaging lies in the improved contrast resolution and ability to qualify several tissue characteristics of a specific organ or lesion. Generally, abdominal MR imaging protocols include precontrast T1-weighted images, T2-weighted images, and dynamic postcontrast T1-weighted images with sufficient imaging redundancy of the organ system in question. Our institution uses organ-specific protocols to facilitate technical reproducibility and optimize scan duration. These protocols are discussed individually in this article when applicable, noting that many build on a basic protocol with slight variations ( Table 1 ).

Table 1

Example protocols

Abdominal/Liver Protocol
	Coronal T2	Axial T2	Axial In/Opposed T1	Axial Fat- Suppressed T2	Axial Diffusion	Axial Pre/Post T1	Axial Dynamic Pre/Post T1
Pulse sequence	SSFSE	SSFSE	SPGR	FSE	SE EPI	SPGR	3D SPGR
Repetition time (ms)	Minimum	Minimum	150	4000	6000	150	Minimum
Echo time (ms)	180	180	2.3/4.6	90	Minimum	Minimum	Minimum
FOV (cm)	40	36	To fit	To fit	40	To fit	To fit
Slice thickness (mm)	8	6	6	6	6	6	4
Matrix	256 × 128	256 × 128	256 × 160	256–320 × 192	128 × 128	512 × 160	320 × 160
Signal averages	0.5 NEX	0.5 NEX	1 NEX	4 NEX	8 NEX	1 NEX	0.5 NEX

MRCP Sequences				Kidney Sequences			Adrenal Sequences
	Axial MRCP	3D MRCP		Axial Water Suppressed T1	Coronal Dynamic Pre/Post T1		Coronal In/Opposed T1
Pulse sequence	SSFSE	FRFSE		SPGR	3D SPGR		SPGR
Repetition true (ms)	Minimum	Minimum		170	Minimum		Minimum
Echo time (ms)	180	650		Minimum	Minimum		2.3/4.6
FOV (cm)	40	36		To fit	To fit		To fit
Slice thickness (mm)	5	1.4		6	3		5
Matrix	256 × 160	256 × 256		256 × 160	320 × 160		256 × 160
Signal averages	0.5 NEX	2 NEX		1 NEX	0.5 NEX		1 NEX

MR Enterography Sequences				MRA Sequences
	Axial Steady-state	Coronal Steady-state		Coronal Dynamic Pre/Post T1	3D Phase Contrast
Pulse sequence	FIESTA	FIESTA		3D SPGR	3D PC
Repetition time (ms)	Minimum	Minimum		Minimum	Minimum
Echo time (ms)	Minimum	Minimum		Minimum	Minimum
FOV (cm)	32–40	38–40		28–40 (prefer 30)	28
Slice thickness (mm)	6	3		2.4	2.5
Matrix	256 × 256	256 × 256		288 × 160	256 × 192
Signal averages	1	1		0.5–1 NEX	1 NEX