MRI and CT in the follow-up after irreversible electroporation of small renal masses.PURPOSE
 Objectives are to assess computed tomography (CT) and magnetic resonance imaging (MRI) on the ablation zone volume (AZV), enhancement and imaging characteristics after renal IRE.


 MRI imaging was performed pre-IRE, 1 week, 3 months, 6 months and 12 months after IRE.  Evolution of AZVs, and relation between the needle configuration volume (NCV; planned AZV) and CT- and MRI volumes were evaluated.


 On MRI, median AZV increased 1-week post-IRE until 3 months post-IRE (respectively, 14.5 cm3 and 4.6 cm3) compared to the NCV (4.8 cm3).  At 6 months the AZV starts decreasing (CT 4.8 cm3; MRI 3.0 cm3), continuing at 12 months (CT 4.2 cm3, MRI 1.1 cm3).  Inter-observer agreement between observers was excellent (CT 95% CI 0.82-0.95, MRI 95% CI 0.86-0.96).  Subtraction images confirmed non-enhancement on MRI in unclear enhancement cases (3/9).  On MRI, the AZV increases at 1 week until 3 months post-IRE.  At 6 months the AZV starts decreasing until 12 months post-IRE on both CT and MRI. 
MRI
MRI and CT in the follow-up after irreversible electroporation of small renal masses.PURPOSE
 Irreversible electroporation (IRE) has the potential, although still experimental, to overcome current limitations of thermal ablation.  No prospective imaging studies exist of the ablation zone in the follow up after renal IRE in humans.  Objectives are to assess computed tomography (CT) and magnetic resonance imaging (MRI) on the ablation zone volume (AZV), enhancement and imaging characteristics after renal IRE.


 Prospective phase 2 study of IRE in nine patients with ten SRMs.  CT was performed pre-IRE, perioperatively (direct after ablation), 3 months, 6 months and 12 months after IRE.  Evolution of AZVs, and relation between the needle configuration volume (NCV; planned AZV) and CT- and MRI volumes were evaluated.


 On CT, median AZV increased perioperatively until 3 months post-IRE (respectively, 16.8 cm3 and 6.2 cm3) compared to the NCV (4.8 cm3).  On MRI, median AZV increased 1-week post-IRE until 3 months post-IRE (respectively, 14.5 cm3 and 4.6 cm3) compared to the NCV (4.8 cm3).  At 6 months the AZV starts decreasing (CT 4.8 cm3; MRI 3.0 cm3), continuing at 12 months (CT 4.2 cm3, MRI 1.1 cm3).  Inter-observer agreement between observers was excellent (CT 95% CI 0.82-0.95, MRI 95% CI 0.86-0.96).  Subtraction images confirmed non-enhancement on MRI in unclear enhancement cases (3/9).  Directly after IRE, gas bubbles, perinephric stranding and edema were observed in all cases.


 The AZV increases immediately on CT until 3 months after IRE.  At 6 months the AZV starts decreasing until 12 months post-IRE on both CT and MRI.  Gas bubbles, perinephric stranding and edema are normal findings directly post-IRE.
CT