MRI Adrenal — chemical shift
Both adrenal glands with the upper abdomen; thin sections through the lesion of interest.
Typical, not policy
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Adrenal incidentaloma that is indeterminate on unenhanced CT (above 10 HU) and needs characterising.
- Adrenal lesion in a patient in whom repeated CT is undesirable, including younger patients.
- A known adenoma requiring interval follow-up.
- Characterisation of a lesion where the CT washout study was equivocal or could not be performed.
Technique
- Dual-echo gradient-echo T1 acquiring in-phase and opposed-phase images in one breath-hold, so that identical regions of interest can be placed on both.
- Echo times must correspond to true in-phase and opposed-phase conditions at the local field strength; the values differ between 1.5 T and 3 T.
- Axial T2 and diffusion for morphology, plus post-contrast imaging only where the lesion is indeterminate.
- Quantitative thresholds are field-strength specific and should not be transferred between 1.5 T and 3 T.
Where it goes wrong
- Separate breath-holds for the two echoes, so regions of interest no longer correspond and the calculated index is meaningless.
- Using the spleen as a reference when splenic signal is itself abnormal, as in iron overload — the ratio then becomes uninterpretable.
- Applying 1.5 T thresholds to a 3 T study.
- Regions of interest placed over the lesion margin, where chemical-shift boundary artefact exaggerates signal drop.
- Requesting adrenal MRI when unenhanced CT already showed a homogeneous lesion of 10 HU or less, which is already diagnostic.
Clinical questions that reach this study
Contrast
None
- The adenoma question is answered unenhanced. Contrast is added only when the lesion is indeterminate and a vascular or invasive characteristic is being sought.
Acquisition
- Breathing
- End-expiratory breath-hold for the dual-echo acquisition, which must be a single breath-hold so that in-phase and opposed-phase images are perfectly registered.
- Reconstruction
- Signal intensity index and adrenal-to-spleen ratio calculated from regions of interest placed identically on both echoes.
- Preparation
- Supply the unenhanced CT attenuation if it exists — a homogeneous lesion of 10 HU or less is already diagnostic and does not need MRI. Include the biochemical results; a functioning lesion is a different pathway from an incidentaloma. Chemical-shift sequences are unenhanced; contrast is not part of the core adenoma question.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- MR safety screening for implants and foreign bodies· radiographer at scan