MRI Pulse Sequences for Spine¶

Definition¶

MRI pulse sequences are specific combinations of radiofrequency pulses and magnetic field gradients that determine the contrast characteristics of the resulting images. Different sequences highlight different tissue properties, and selecting the appropriate sequences is essential for accurate spine evaluation.

Core Sequences¶

T1-Weighted Imaging¶

Contrast mechanism: reflects differences in T1 relaxation times; tissues with short T1 (fat, gadolinium, methemoglobin) appear bright
Key features: excellent anatomic detail; fat is bright; CSF is dark; marrow is bright (adult fatty marrow)
Spine applications: marrow evaluation, foraminal anatomy (bright epidural fat outlines dark nerve roots), post-contrast enhancement detection

T2-Weighted Imaging¶

Contrast mechanism: reflects differences in T2 relaxation times; tissues with long T2 (water, CSF) appear bright
Key features: CSF is bright ("myelographic effect"); fluid/edema is bright; normal cord is intermediate
Spine applications: disc evaluation (hydration = bright, desiccation = dark), stenosis assessment, cord signal abnormalities, detection of edema and fluid collections

STIR (Short Tau Inversion Recovery)¶

Contrast mechanism: an inversion recovery sequence that selectively suppresses fat signal while highlighting water/edema
Key features: fat is dark (suppressed); edema and fluid are very bright; extremely sensitive to pathology
Spine applications: bone marrow edema (acute fractures, metastases, infection), ligamentous injury, inflammatory disease

Proton Density (PD)¶

Contrast mechanism: reflects the number of mobile hydrogen protons per unit tissue
Key features: intermediate contrast between T1 and T2; not commonly used in spine MRI as a primary sequence
Spine applications: occasionally used for disc evaluation and cartilage assessment

Advanced Sequences¶

Gradient Echo (GRE)¶

Fast acquisition with T2*-weighted contrast
Sensitive to magnetic susceptibility effects (blood products, calcification, metallic artifact)
Used for detecting hemorrhage in the cord and evaluating cord compression in cervical spondylotic myelopathy
Blooming artifact near metallic hardware limits use in post-surgical patients

Diffusion-Weighted Imaging (DWI)¶

Measures the random motion of water molecules (Brownian motion)
Restricted diffusion (bright on DWI, dark on ADC map) indicates dense cellularity or cytotoxic edema
Spine applications: differentiating acute vertebral compression fracture (restricted) from chronic fracture (no restriction); abscess detection; tumor characterization

Fat-Saturated Sequences¶

Chemical fat saturation: applies a frequency-selective pulse to suppress fat signal; used with T2 and post-contrast T1
Dixon technique: separates water and fat signals mathematically; more uniform fat suppression than chemical saturation
Used to confirm that bright T1 signal is due to fat (signal drops with fat sat) vs. other causes (blood, protein)

T2* (T2-Star)¶

A gradient echo-based sequence sensitive to magnetic field inhomogeneities
Useful for detecting hemorrhage, calcification, and metallic fragments
Can help identify intramedullary hemorrhage in acute spinal cord injury

Sequence Selection by Clinical Scenario¶

Clinical Question	Essential Sequences
Disc herniation	Sagittal T2, Axial T2, Sagittal T1
Spinal stenosis	Sagittal T2, Axial T2, Sagittal T1
Acute fracture	Sagittal STIR (edema detection), Sagittal T1 (fracture line)
Metastatic disease	Sagittal STIR, Sagittal T1, Post-contrast T1 fat-sat
Infection	Sagittal STIR, Sagittal T1, Post-contrast T1 fat-sat (essential)
Post-surgical	Post-contrast T1 fat-sat (scar enhances, recurrent herniation does not)
Cord lesion	Sagittal T2, Sagittal T1, Post-contrast T1, DWI
Trauma (ligaments)	Sagittal STIR, Sagittal T2

Clinical Pearl

The key to distinguishing recurrent disc herniation from post-surgical scar tissue is gadolinium-enhanced T1 with fat saturation. Scar tissue enhances uniformly and early (within 5 minutes), while recurrent disc herniation does not enhance centrally (only peripheral enhancement may be seen). This distinction is critical because scar tissue is typically not surgically treated, while symptomatic recurrent herniation may require reoperation.

Key Points¶

T1 shows anatomy (fat bright, CSF dark); T2 shows pathology (fluid bright, CSF bright)
STIR is the most sensitive sequence for edema and is essential for acute fractures, infection, and inflammation
DWI helps differentiate acute from chronic compression fractures
Post-contrast T1 with fat saturation is essential for tumor, infection, and post-surgical evaluation
Sequence selection should be tailored to the clinical question
Sagittal T2 is the single most important screening sequence for spine MRI

References¶

Bitar R, Leung G, Perng R, et al. MR pulse sequences: what every radiologist wants to know but is afraid to ask. RadioGraphics. 2006;26(2):513-37. https://pubmed.ncbi.nlm.nih.gov/16549614/
Jo S, Sammet S, Thomas S, Stacy GS. Musculoskeletal MRI pulse sequences: a review for residents and fellows. RadioGraphics. 2019;39(7):2038-2039. https://pubmed.ncbi.nlm.nih.gov/31697620/
Ross JS. Newer sequences for spinal MR imaging: smorgasbord or succotash of acronyms? AJNR Am J Neuroradiol. 1999;20(3):361-373. https://pmc.ncbi.nlm.nih.gov/articles/PMC7056070/
Del Grande F, Santini F, Herzka DA, et al. Fat-suppression techniques for 3-T MR imaging of the musculoskeletal system. RadioGraphics. 2014;34(1):217-233. https://pmc.ncbi.nlm.nih.gov/articles/PMC4359893/
Shah LM, Hanrahan CJ. MRI of spinal bone marrow: part 1, techniques and normal age-related appearances. AJR Am J Roentgenol. 2011;197(6):1298-1308. https://pubmed.ncbi.nlm.nih.gov/22109283/
Radiopaedia. MRI sequences (overview). https://radiopaedia.org/articles/mri-sequences-overview
Radiopaedia. Fat suppressed imaging. https://radiopaedia.org/articles/fat-suppressed-imaging