Proton, diffusion-weighted imaging, and sodium (23Na) MRI of uterine leiomyomata after MR-guided high-intensity focused ultrasound: a preliminary study

Abstract

Purpose: To determine the feasibility of using combined proton (1H), diffusion-weighted imaging (DWI), and sodium (23Na) magnetic resonance imaging (MRI) to monitor the treatment of uterine leiomyomata (fibroids).

Materials and methods: Eight patients with uterine leiomyomata were enrolled and treated using MRI-guided high-intensity frequency ultrasound surgery (MRg-HIFUS). MRI scans collected at baseline and posttreatment consisted of T2-, T1-, and 1H DWI, as well as posttreatment 23Na MRI. The 23Na and 1H MRi were coregistered using a replacement phantom method. Regions of interest in treated and untreated uterine leiomyoma tissue were drawn on 1H MRI and DWI, wherein the tissue apparent diffusion coefficient of water (ADC) and absolute sodium concentrations were measured.

Results: Regions of treated uterine tissue were clearly identified on both DWI and 23Na images. The sodium concentrations in normal myometrium tissue were 35.8+/-2.1 mmol (mM), in the fundus; 43.4+/-3.8 mM, and in the bladder; 65.3+/-0.8 mM with ADC in normal myometrium of 2.2+/-0.3x10(-3) mm2/sec. Sodium concentration in untreated leiomyomata were 28+/-5 mM, and were significantly elevated (41.6+/-7.6 mM, P<0.05) after treatment. Apparent diffusion coefficient values in the treated leiomyomata (1.30+/-0.38x10(-3) mm2/sec) were decreased compared to areas of untreated leiomyomata (1.75+/--4048micro-4050micro36x10(-3) mm2/sec; P=0.04).

Conclusion: Multiparametric imaging permits identification of uterine leiomyomata, revealing altered 23Na MRI and DWI levels following noninvasive treatment that provides a mechanism to explore the molecular and metabolic pathways after treatment.

Copyright (c) 2009 Wiley-Liss, Inc.

Figures

Figure 1

Representative example of an MR–guided high intensity focused ultrasound surgery (MRg-HIFUS) treatment plan. a) The treatment plan outlined using green cylinders on the targeted leiomyoma. b) Axial T2 (TR/TE=5000,100ms) MR images with the cylinders and fans (near and far zones) show the treatment area of the high-intensity focused ultrasound beam. The blue fan area shows each individual treatment area and the underlying structures that may be affected, and demonstrates the ability to “tilt” the ultrasound unit to obtain adequate coverage. c) Sagittal T2 MR image at the same location.

Figure 2

Representative T2-weighted (top) and 23NA (bottom) MR images from a normal participant. a) Normal uterine tissues (fundus) were isointense on baseline T2WI (TR/TE=3000/98ms) and the bladder was hyperintense. b) Different regions of the uterus can be identified on the sodium images, where the myometrium is hyperintense, as are the bladder and the ovaries.

Figure 3

Representative T1-weighted and 23NA MR images from a baseline study. a) Uterine leiomyomata were isointense to hypointense on baseline T1WI (TR/TE=185/1.5ms) (left). b) Different regions of the uterus can be identified on the 23NA images, where the leiomyoma appears isointense, whereas, the myometrium is hyperintense, as is the bladder.

Figure 4

Representative post-contrast T1-weighted, diffusion-weighted, 23NA, and T2-weighted images of a leiomyoma. a) On pre-treatment MR images, there is contrast enhancement on the T1-weighted image (TR/TE=185/1.5ms) in the leiomyoma. On DWI (b=1000), the leiomyoma is isointense at this time point. The T2-weighted image (TR/TE=5000/90ms) shows small regions of hyperintensity with the leiomyoma. b) After MRg-HIFUS treatment, the T1 shows decreased contrast uptake within the treated region and decreased signal intensity on the ADC map. The T2-weighted images demonstrate increased signal intensity, indicative of vasogenic edema. c) The 23NA images show marked increase in total sodium concentration. Taken together, both the proton (T1, DWI, T2) and 23NA images demonstrate the potential of multiparametric and multinuclear imaging to characterize leiomyoma treatment.

Figure 5

Representative post-contrast T1-weighted, diffusion-weighted, 23NA, and T2-weighted images from a patient undergoing MRg-FUS. a) On pre-treatment MR images, there is contrast enhancement on the T1-weighted image (TR/TE=185/1.5ms) within the leiomyoma and little or no signal changes on the DWI (isointense) and the ADC map. In addition, the T2-weighted images (TR/TE=5000/90ms) do not show any regions of hyperintensity with the leiomyoma. b) As expected, after treatment, the post-contrast T1 shows a focal area of hypointensity that corresponds to decreased contrast uptake within the treated region. This focal region of treated tissue is also well demarcated on the T2-weighted image DWI (b=1000) and on the ADC map. c) Similarly, increased signal intensity on the 23NA images in the same focal region within the treated area is observed. However, there is a bright focus on the 23NA images corresponding to a fluid/cystic follicle at the 2:00 position outside the treatment area and is not related to the treatment.

Figure 6

Bar graphs of the apparent diffusion coefficient of water (ADC) derived from the diffusion weighted imaging in untreated and treated uterine leiomyoma tissue. There was a significant decrease (p

Figure 7

Bar graphs of sodium concentration in millimolar (mM) in uterine fatty, leiomyoma tissue and in treated uterine leiomyoma tissue. After treatment, there was a significant increase (p