Accurate localization of MRI-visible index lesions is essential for focal or targeted ablation, and integration of systematic and targeted biopsy findings is required to delineate the true extent of disease (Fig. 4). Focal ablation is most appropriate when the dominant clinically significant tumor is MRI-visible and concordant with biopsy localization. In cases of extensive, multifocal, or MRI-invisible disease, whole-gland TULSA is more commonly considered (Fig. 3); in such settings, accurate delineation of the prostatic contour is critical, necessitating high-quality T2WI.

Definite EPE generally precludes focal therapy [15]. Recurrence involving the seminal vesicles after treatment has been reported and likely reflects pre-existing disease that was not adequately captured at baseline [10]. Evaluation is based on established imaging criteria [16], with contrast-enhanced imaging playing an important role in the assessment of SVI [17, 18].

Experimental and early clinical studies suggest that ablation beyond the prostatic capsule is technically feasible [19]. Accordingly, in equivocal cases, inclusion of adjacent extraprostatic tissue within the treatment volume with adequate margins may be considered (Fig. 6).

Tumor extent and critical structures for treatment planning. A Pre-treatment axial T2WI (upper right) demonstrates an index lesion in the posterior apical peripheral zone at the 6-o’clock position with EPE (arrow). An axial T2WI obtained 5 mm caudal to this level shows the external urethral sphincter as a low-signal-intensity ring (arrowheads) surrounding the urethra. On coronal T2WI (upper right), the external urethral sphincter is visualized as paired low-signal-intensity muscular bundles (arrowheads) along the membranous urethra. DWI (bottom left) and DCE (bottom middle) clearly demonstrate the extent of the lesion. B Corresponding treatment planning (orange contour, left) and immediate post-treatment contrast-enhanced T1WI (middle) demonstrate a well-defined NPV extending into the extraprostatic space in the dorsal aspect of the apex (open arrow). At 3 months after TULSA, coronal T2WI (right) shows a cavitated treated area extending close to the external urethral sphincter (arrowheads), without definite disruption of the sphincter complex. C Pre-treatment mpMRI (T2WI [left], DWI [middle], and DCE [right]) demonstrates focal thickening of the seminal vesicle wall (arrow) contiguous with the index tumor (not shown), suggesting SVI. D Corresponding thermal dose map (left) and immediate post-treatment contrast-enhanced T1WI (right) demonstrate extension of the planned ablation area to the region suspicious for SVI (black ROI), resulting in decreased enhancement in the central portion of the seminal vesicle (open arrow)

Preservation of the neurovascular bundles (NVBs; erectile function), external urethral sphincter (active continence, particularly during increases in abdominal pressure), and bladder neck (passive outlet resistance during bladder filling) is critical for functional outcomes [20].

On T2WI, the NVBs are identified as paired posterolateral structures along the prostate capsule, typically at the 5- and 7-o’clock positions, appearing as small curvilinear or punctate low-signal-intensity structures within the periprostatic fat (Fig. 3A) [16]. The external urethral sphincter is visualized as a low-signal-intensity striated muscular ring surrounding the membranous urethra (Fig. 6A), whereas the bladder neck appears as a funnel-shaped smooth muscle structure at the bladder base [21, 22].

Calcifications within the planned ultrasound beam path can attenuate or distort acoustic propagation and alter heat deposition, increasing the risk of incomplete ablation [12]. Pre-procedural detection is therefore important, particularly for large (approximately > 3 mm) calcium deposits that intersect the intended ablation path, although the clinical significance of a calcification depends on its size, density, and location relative to the intended beam path. Identification with CT or calcification-sensitive MR techniques is therefore critical (Table 2). Pre-treatment removal may be required [23].

Thrombus or slow flow within the periprostatic venous plexus may mimic PCa on DWI, appearing as focal or round structures with low signal intensity on T2WI, mild diffusion restriction, and occasionally increased signal on high b-value DWI. Therefore, careful multiparametric assessment is required [24]. Evaluation in multiple planes typically demonstrates continuity with adjacent vessels, and lack of early focal enhancement on DCE helps distinguish these findings from PCa.