Bollow et al used magnetic resonance imaging (MRI) to evaluate patients with sacroiliitis associated with spondyloarthropathy. The authors are from Humboldt-Universitat and Freie Universitat Berlin in Germany.
Examination: MRI of sacroiliac joints
Indices:
(1) chronicity index in precontrast images
(2) MRI activity index from contrast enhanced images
Chronicity Index
Changes in Sacroiliac Joints
Grade
no chronic inflammatory changes
0
mild subchondral sclerosis without sclerosis-related blurring of the articular cavity on T1-weighted images with or without fat accumulation AND/OR
1 erosion ("fewer than 2")
I
moderate subchondral sclerosis with sclerosis-related blurring of less than one-third of the articular cleft on T1-weighted images with or without periarticular fat accumulation AND/OR
more than 2 discrete erosions without confluence
II
pronounced subchondral sclerosis with blurring of more than one third of the articular cleft on T1-weighted images with or without periarticular fat accumulation AND/OR
confluent erosions with pseudodilatation of the articular cavity AND/OR
circumscribed "anklyosis buds" involving less than one quarter of the articular cavity
III
definite ankylosis involving > 25% of articular cavity; in chronic disease the articular cavity will be filled with fat marrow-like tissue
IV
where:
• Blurring in the image may be due to sclerosis or juxtacortical osteitis. The former shows low signal intensity on both T1 and T2 weighted images and does not show contrast enhancement. The latter shows a high signal in T2 weighted images and contrast enhancement.
MRI Activity Index after Contrast Enhancement
Enhancement Factor (F-enh) in percent =
= (postcontrast signal intensity of the highest curve point before the plateau phase) - (precontrast signal intensity)) / (precontrast signal intensity) * 100%
Enhancement Factor
Inflammatory Activity
Grade
<= 25%
none
X
25.01 - 70%
moderate
A
> 70%
pronounced
B
where:
• Calculation of the Enhancement Factor (F-enh) factor and the Enhancement Slope (S-enh) are described on page 514:
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