Image quality of MR-Imaging on the MR-High Intensity Focused Ultrasound breast system

Breast cancer is the most frequently occurring malignant disease in women
worldwide, comprising 16% of all female cancers2. Nowadays, breast conserving
therapy is standard of care for patients with localized breast cancer1.
However, there is growing interest in less invasive treatment techniques, such
as radiofrequency ablation, laser ablation and cryoablation. Another new and
completely non-invasive treatment modality is Magnetic Resonance guided High
Intensity Focused Ultrasound3, 4. With this technique, a focused ultrasound
beam is used to thermally ablate tissue, while MRI is employed to aim the
ultrasound focus on the lesion and for continuously measuring temperature maps
to ensure optimal safety. Breast lesions are considered especially suited for
treatment with MR-HIFU due to clear visualization of breast lesions with MRI
and the peripheral location of the breast which allows safe targeting.
Philips Healthcare developed a dedicated breast system for thermal ablation of
lesions in the breast. The system consists of a table top which houses multiple
HIFU transducer arrays and a RF receive coil. The system was designed to dock
on top of a standard 1.5-T MRI scanner. Recently, a prototype of this system
was installed in the UMC Utrecht.
Patients will lie prone on the tabletop of the breast system with the target
breast hanging in a cup filled with water. The breast cup is filled with water
to enable ultrasound waves to enter the breast without reflection. Previous
studies have shown that MR-HIFU is feasible and safe in patients with breast
cancer5-9. However, non of these studies included a large number of patients
and complete necrosis was achieved in only 20-50% of patients.
The Philips MR-HIFU breast system differs from the systems previously used for
breast tumor ablation. Eight separate transducers are circumferentially
positioned around the breast cup. This method of lateral sonication reduces the
risk of heating heart and lungs, and the wide aperture of the transducer
reduces the risk of skin heating. The MR-HIFU breast system uses a volumetric
ablation method, which can induce larger and more homogeneous ablation volumes
per sonication and a reduction in treatment time. This is why we think we can
achieve better results than previous studies using other systems.
Our final goal is to treat patients with breast cancer using the MR-HIFU breast
system, but we have to go through several steps before we can start with
MR-HIFU ablation in patients with breast cancer. First, it is very important to
assess the quality of images acquired on the MR-HIFU system. This is necessary
since the integration of the HIFU transducer into the MR table top made it
necessary to develop a new RF receive coil with different imaging capacities
from the coils normally used for breast MRI.
In a second study, we are going to compare image quality and lesion
characteristics between a CE-MRI on the MR-HIFU breast system and a
conventional 3-Tesla CE-MRI in patients with breast cancer.
In a third study, we intend to start MR-HIFU ablation in patients with
symptomatic fibroadenomas to assess the accuracy and safety of the MR-HIFU
breast system.
Ultimately, we plan to perform MR-HIFU ablation in patients with breast cancers
to assess the efficacy of the MR-HIFU breast system in a treat-and-resect
study.
The current protocol aims on the assessment of the quality of MR-imaging on the
MR-HIFU breast system in healthy volunteers and in patients with a fibroadenoma
relative to the quality of MR-imaging on a conventional diagnostic MRI scanner.
We chose to start with imaging of volunteers, because no imaging of human
beings has been done on the Philips MR-HIFU breast system with the water box
filled with water. We focus on quality of MR-imaging on the MR-HIFU breast
system in patients with fibroadenomas, because this will be the first cohort of
patients we intend to treat with MR-HIFU. Fibroadenomas are benign tumors in
the breast, are visible on a T2-weighted image without the use of a contrast
agent, and do not require surgical excision from a medical point of view.

In conclusion, as a first step it is very important to compare quality of
images acquired on the MR-HIFU breast system with images acquired on a
conventional diagnostic 3-Tesla MRI scanner. In the future, when evaluating
patients eligible for treatment with MR-HIFU, patients will always be evaluated
based on a conventional diagnostic 3T MRI. Therefore, it is very important to
assess differences between the two scans, both in healthy volunteers and in
patients with a fibroadenoma.

Primary objectives
What is the quality of MR images acquired on the MR-HIFU breast system in
volunteers and patients with a fibroadenoma relative to the quality of MR
images acquired on a conventional diagnostic 3-Tesla MRI scanner? We will
assess the image quality in terms of:
- delineation of anatomical structures such as fibroglandular tissue, fatty
tissue and muscles
- contrasts between various anatomical structures
- SNR (signal to noise ratio)
- quantity and variety of artefacts.
What is the quantitative assessment of the lesion according to the Breast
MRI-lexicon criteria of the American College of Radiology (ACR) of both MRI
scans in patients with a fibroadenoma?

Secondary objectives
What is the geometric deformation of the breast on the MR-HIFU breast system in
volunteers and patients with a fibroadenoma relative to the MR images acquired
on a diagnostic 3-T MRI scanner and its association with breast size?
What is the size and position of a fibroadenoma in patients on images acquired
on the MR-HIFU breast system compared to the size and position on MR images
acquired on a 3-T MRI scanner?

The study is designed as a single-centre, single arm, prospective, cohort study
to evaluate the image quality of MR images acquired on the MR-HIFU breast
system in volunteers and patients with a fibroadenoma. All volunteers and
patients will be included in the University Medical Center Utrecht.

Volunteers and patients will undergo MR imaging on the MR-HIFU breast system
and on a 3-T MRI scanner, both without the use of a contrast agent. There are
no direct benefits for the subjects participating in this research, but the
risks are considered minimal.