Overview
The Emprint HP (Medtronic) is a percutaneous microwave ablation (MWA) system operating at 2.45 GHz, designed for thermal ablation of soft tissue tumours. It utilises Thermosphere technology to deliver predictable, spherical ablation zones. The system is widely deployed across UK cancer centres for the treatment of hepatic, renal and pulmonary malignancies.
Indications
Primary hepatocellular carcinoma (within Milan criteria or bridging to transplant)
Hepatic metastases (particularly colorectal, up to 3 cm diameter)
Renal cell carcinoma (T1a tumours up to 4 cm)
Primary and secondary pulmonary malignancies
Painful osseous metastases (palliative)
System Components
Generator — 150 W solid-state microwave generator with touchscreen interface
Antennas — single-use percutaneous antennas available in 13 ga and 15 ga, lengths 15–30 cm
Thermosphere technology — proprietary field control, thermal control, and wavelength control for predictable spherical ablation zones
Ablation Zone Specifications
| Power (W) | Time (min) | Expected Zone (cm) |
|---|---|---|
| 75 | 2 | 2.2 × 1.8 |
| 75 | 5 | 3.0 × 2.5 |
| 100 | 5 | 3.5 × 3.0 |
| 100 | 10 | 4.5 × 3.8 |
| 150 | 10 | 5.0 × 4.2 |
Note: Actual ablation zones vary with tissue perfusion, organ type, and proximity to heat sinks (large vessels).
Key Features
Spherical ablation zones — Thermosphere technology reduces the elongated "comet tail" zones seen with older MWA systems
Multi-antenna capability — up to 3 antennas can be powered simultaneously for larger tumours
No ground pads required — unlike radiofrequency ablation, simplifying patient set-up
Less susceptible to heat-sink effect — MWA performs better than RFA near large vessels
Technique Tips
Plan the ablation zone to include a minimum 5–10 mm circumferential margin beyond the tumour boundary (A0 margin).
For hepatic lesions, CT guidance with contrast-enhanced planning is standard. Use cone-beam CT (CBCT) if available for real-time needle confirmation.
Hydrodissection (D5W or saline) can be used to protect adjacent structures such as bowel, diaphragm, or gallbladder.
Renal ablations are typically performed prone under CT guidance. Aim to position the antenna through the maximum tumour diameter.
For lung lesions, use a shorter ablation time and lower power to reduce the risk of pneumothorax expansion. Position the patient with the lesion side down post-procedure.
Track ablation is recommended on withdrawal to reduce bleeding risk and potential tract seeding.