Table 1.
Imaging modalities for thyroid orbitopathy and their characteristics
| Imaging modality | Type of signal | Dangers | Utility in TED | Advantages | Disadvantages | Provides a quantifiable marker of disease activity? |
|---|---|---|---|---|---|---|
| CT | X-ray | Radiation- and iodine-based contrast | Better than MRI at identifying enlarged muscles [23]. Density of muscles can correlate with disease [24] | Fast. Better bone resolution than MRI. Good for assessment of apical crowding [1] | Radiation. Volumetry of muscles may not correlate with disease activity [25] | Mainly proptosis |
| MRI | Nuclear magnetic resonance | Patients with certain active or passive implants may be contraindicated | Better than CT at identifying areas of inflammation in muscle | Better contrast between soft tissues than CT. Different sequences provide specific anatomical or physiological information | Slow. Acoustic noise. Costly. Movement artefacts | Potentially, but most clinical protocols provide qualitative or semi-quantitative data |
| Ultrasound | Sound echo | None | Limited | Rapid. Available. Can perhaps exclude scleritis and intraocular pathology | User-dependent. Limited depth. No visualisation of apex. Limited reproducibility | No |
| Doppler | Sound echo | None | Limited clinical utility but blood flow in superior ophthalmic vein is reduced in TED [26] | Rapid. Available | Difficult to perform. Inter-observer variability. Not specific for TED | No |
| Octreoscan with 111In | γ-Ray scintigraphy | High radiation | Limited | Orbital uptake of this labelled somatostatin analogue is greater in TED | Non-specific. High cost. Poor availability. Requires careful standardisation | No |
| Octreoscan with 99Tm | γ-Rray scintigraphy | Lower radiation | Limited. But significant correlation was found between CAS and the orbital uptake. Identifies active disease | Lower cost. Greater availability. Higher energy so improved resolution. Shorter acquisition time | Radiation. Invasive | No |
| Gallium-67 scintigraphy | γ-Ray scintigraphy | Radiation | Limited. Able to detect response to treatment | Equivalent positive predictive value to octreotide and T2-relaxation time on MRI | Invasive. Requires careful standardisation | No, too difficult |
| FDG-PET/CT | Positron scintigraphy | Radiation | Limited but able to identify activity even when MRI normal [27] | May detect early/subclinical disease | Radiation. Not widely used | No |
| Thermal | Heat | None | Limited. But higher temperatures recorded in TED | Non-invasive. Changes in response to IV steroids [28] | Low specificity. Requires complex equipment to measure accurately | No, too much variability |