The potential role of dynamic MRI in assessing the effectiveness of high-intensity focused ultrasound ablation of breast cancer

Figures & data

Figure 1. Diagrams of technical effectiveness. (A) Illustration of HIFU therapy. (B) Illustration of the technical effectiveness as divided into complete versus partial ablation. (C) Illustration of the technical effectiveness as depicted on a MR subtraction image: thin rim enhancement for complete ablation and nodular or irregular thick enhancement for partial ablation.

Table I.  Ablation parameters of HIFU.

Pt.No.	Age	Size (mm)^#	First HIFU					Second HIFU
			Date	Power (W)	No. of 5-mm sections*	Procedure time	Sonification time (s)	Date	Power (W)	No of 5-mm sections*	Procedure time	Sonification time (s)
1	49	12	Apr	120–182	8	2 h 35 min	2038	–
2	47	37	Jun	100–240	13	2 h 50 min	1942	–
3	52	33	Aug	80–220	12	4 h 45 min	3677	–
4	68	15	Mar	100–240	9	1 h 20 min	1942	–
5	60	35	Aug	120–180	13	3 h 50 min	2845	Dec	100–200	11	3 h 15 min	2074
6	46	22	Sep	200–220	10	2 h 15 min	2088	Dec	140–180	10	2 h 25 min	3831

Pt no., patient number.

^#Mass size was the longest diameter of the tumour on dynamic MRI at the time of ablation.

*Number of 5–mm sections needed to ablate the index tumour and margin.

Table II.  Summary of MRI findings and pathology after HIFU procedure.

Pt. No.	1st HIFU/2nd HIFU			FU MRI
	MRI post-HIFU	Bx or Op Pathology	2nd HIFU	FU period (months)	Enhancement	Index tumour size	Pathology
1	Thin rim	–	N/A	3,5,7,10,18,25,30	Thin rim	12 → 5 mm (12 M)	No viable tumour at Bx (20 M)
2	Thin rim	–	N/A	2,6,12,18,24	Thin rim	37 → 15 mm (24 M)	No viable tumour at Bx (8 M)
3	Thin rim	–	N/A	2,4,11	Thin rim	33 → 26 mm (11 M)	No viable tumour at ablated lesion and multifocal IDC apart from index mass at Op (11 M)
4	Nodular	Viable tumour at Bx	N/A	–			Viable tumour at Op (3 M)
5	Nodular/*	Viable tumour at Bx/–	Yes	–			Viable tumour at Op (1 M after 2nd HIFU)
6	Nodular/thin rim	–/–	Yes	2 after 2nd HIFU			No viable tumour at Op (3 M after 2nd HIFU)

Pt, patient; nodular-nodular or irregular thick enhancement; Bx, US-guided core needle biopsy; Op, mastectomy; IDC, invasive ductal carcinoma; M, month; N/A, not applicable.

The MRI post-HIFU was performed at two weeks after the HIFU, and the FU MRI was performed serially after 2 or 3 months following the HIFU.

*MRI after a second HIFU session was not performed.

Figure 2. Dynamic MRI findings of patient 1 mentioned in Table II. (A) An early post-contrast sagittal T1-weighted image prior to HIFU showed a 12 mm, irregular enhancing mass (arrow). (B) A pre-contrast axial T1-weighted image of MRI post-HIFU revealed an isointense index tumour (arrow). (C) An early post-contrast sagittal T1-weighted image of MRI post-HIFU revealed an index tumour, isointense to adjacent parenchyma (arrow). It was surrounded by an ablation zone of decreased signal intensity (arrowheads). (D) The ablation zone on a delayed subtraction image of MRI post-HIFU was demarcated by dark signal intensity. Although no enhancement of the index tumour was observed, an incomplete thin rim enhancement was present (arrowheads). (E) An early post-contrast sagittal T1 weighted image of 12 months FU MRI, the size of the index tumour (arrow) had decreased to 5 mm. (F) The size of the ablation zone surrounded by a thin rim enhancement (arrowheads) had also decreased on a delayed subtraction image of 30 months FU MRI.

Figure 3. Partial ablation in a 68-year-old woman (patient 4 mentioned in Table II). (A) An early post-contrast sagittal T1-weighted image prior to HIFU showed a 15 mm irregular enhancing mass (arrow). (B) An axial fat suppressed T2-weighted image prior to HIFU revealed an isointense index tumour (arrow). (C) An axial fat suppressed T2-weighted image of MRI post-HIFU showed an isointense index tumour (arrow) with mammary oedema. (D) An early post-contrast sagittal T1-weighted image of MRI post-HIFU revealed an index tumour, isointense to adjacent parenchyma (arrow) surrounded by an ablation zone of decreased signal intensity (arrowheads). Irregular enhancement was seen at the periphery of the ablation zone (black arrow). (E) A central dark signal intensity and a nodular or irregular thick enhancement (arrow) was observed on the early and delayed subtraction image of MRI post HIFU. (F) Kinetic curve pattern showed early rapid enhancement and delayed persistent pattern. (G) Photomicrograph of a mastectomy specimen showing prevalent coagulative necrosis and a small portion of viable tumour (arrows) (H and E, original magnification × 40).

Figure 4. Complete ablation and mammary oedema in a 52-year-old woman (patient 3 mentioned in Table II). (A) On an axial fat suppressed T2-weighted image of MRI post-HIFU, mammary oedema (arrow) was accompanied by skin and trabecular thickening and thermal injury was observed as irregular hyperintensity within the chest wall muscle (arrowhead). (B) On an axial fat suppressed T2-weighted image of 6 months FU MRI, mammary oedema and chest wall muscle change almost disappeared. (C) The subtraction image of 11 months FU MRI showed a central dark signal intensity and a thin rim enhancement (arrow). Thin rim enhancement was faint on early subtraction image, but was more prominent on the delayed subtraction image. (D) Photomicrograph of mastectomy specimen shows coagulative necrosis (arrows) and peripheral foreign body reaction (arrowheads) (H and E, original magnification × 1). No viable tumour was present in the ablation zone

Figure 5. Partial ablation in a 60-year-old woman (patient 5 mentioned in Table II). (A) A central dark signal intensity and a nodular or irregular thick enhancement (arrow) was observed on the early subtraction image of MRI post HIFU. (B) Kinetic curve pattern showed early rapid enhancement and delayed washout pattern.