What is CT Arthrogram with IMAR?
CT arthrogram with IMAR refers to a CT arthrography examination performed after intra-articular injection of a mixture containing both iodinated contrast (for CT visualization) and paramagnetic/gadolinium-based contrast (for potential MR imaging), allowing both CT and MR arthrography to be performed from a single joint injection.
Technical Overview
The "IMAR" terminology appears to reference "Intra-articular Magnetic-resonance-type contrast," which describes a combined contrast injection technique. This approach involves:
- Single injection protocol: CT-guided intra-articular injection of a mixture containing both iodinated contrast agent (e.g., iobitridol) and paramagnetic/gadolinium-based contrast agent (e.g., gadodiamide) diluted in saline 1
- Dual imaging capability: After the single injection, both CT arthrography and MR arthrography can be performed sequentially
- Typical mixture ratios: Studies have used gadodiamide at 1:250 dilution and iobitridol 350 at 1:5 dilution in 20 ml saline solution 1
Clinical Applications
This technique has been studied primarily for shoulder joint evaluation, where it allows:
- Comprehensive joint assessment: Evaluation of labral tears, rotator cuff pathology, cartilage lesions, and capsular structures 1, 2
- Complementary information: The combined CT-MR arthrography approach provides more diagnostic information than either modality alone, with significantly better agreement with arthroscopic findings 1
- Joint distension benefit: Improved contrast and joint distension optimize evaluation of intra-articular structures and help distinguish normal variants from true pathology 2
Safety Profile
The technique has demonstrated a favorable safety profile with no reported side effects in clinical studies 1. Injection volumes typically range from 10-24 ml depending on the joint and patient factors.
Current Clinical Context
According to recent ACR guidelines, while standard CT arthrography (with iodinated contrast only) and MR arthrography (with gadolinium only) are recognized as appropriate imaging modalities for specific joint pathology 3, the combined "one-shot" technique remains primarily a research tool rather than standard clinical practice. Most clinical scenarios use either CT arthrography OR MR arthrography separately, not the combined injection approach.
When Standard CT Arthrography is Appropriate:
- Detailed evaluation of labral pathology when MRI is contraindicated 3
- Assessment of intra-articular fracture fragments 4
- Evaluation of cartilage lesions and loose bodies 5
Important Caveat:
The term "IMAR" is not standard medical nomenclature in current guidelines. If you encounter this term in a clinical order or report, clarify with the ordering provider or radiologist whether they are requesting standard CT arthrography or the specialized combined contrast technique, as the latter requires specific protocol preparation and may not be routinely available at all imaging centers.