Bilateral open breast coil and compatible intervention device

Breast intervention device for low-field MRI with a customized unilateral coil

With the incidence of breast cancer rising to the top among female malignant tumors, magnetic resonance images guided breast biopsy intervention and minimally invasive treatment have developed as a clinically practical research issue. High field studies have shown the diagnostic value of breast MRI, but the examination costs greatly exceed those of competing conventional mammography. In this case, low-field MRI cannot merely provide typical MRI contrast, but also significantly reduce the cost of diagnosis and treatment for breast cancer patients. This work describes a unilateral breast coil and prototype intervention device, which provides a customized solution for low-field MRI-guided breast intervention. Results demonstrate that the low-field MRI breast intervention device facilitates medical intervention procedures. And the designed positioning device can locate the target lesion within 2-3 mm accuracy. Phantom tests with the customized unilateral coil indicate that the open loops perform as well as the 4-channel commercial closed breast coil, presenting a relatively good SNR (signal-to-noise ratio) and uniformity characteristics. MR scanning images of the volunteer breast using the breast intervention coil also show high SNR, which lays a foundation for further implementation of image-guided breast interventional minimally invasive surgery with the low-field MRI system.

Assessment of a carbon fibre MRI flatbed insert for radiotherapy treatment planning

OBJECTIVE

The purpose of this work was to assess heating and radiofrequency (RF) deposition and image quality effects of a prototype three-section carbon fibre flatbed insert for use in MRI.

METHODS

RF deposition was assessed using two different thermometry techniques, infrared thermometry and Bragg-grating thermometry. Image quality effects were assessed with and without the flatbed insert in place by using mineral oil phantoms and a human subject.

RESULTS

Neither technique detected heating of the insert in typical MRI examinations. We found that the insert was less suitable for MRI applications owing to severe RF shielding artefact. For spin-echo (SE), turbo spin-echo (TSE) and gradient-echo sequences, the reduction in signal-to-noise ratio (SNR) was as much as 89% when the insert was in place compared with the standard couch, making it less suitable as a patient-support material. Turning on the MultiTransmit switch together with using the scanner's quadrature body coil improved the reduction in SNR from 89% to 39% for the SE sequence and from 82% to 12% for the TSE sequence.

CONCLUSION

No evidence was found to support reports in the literature that carbon fibre is an unsuitable material for use in MRI because of heating.

ADVANCES IN KNOWLEDGE

This study suggests that carbon fibre is less suitable for large-scale MRI applications owing to it causing severe RF shading. Further research is needed to establish the suitability of the flatbed for treatment planning using alternative sequences or whether an alternative carbon fibre composite for large-scale MRI applications or a design that can minimize shielding can be found.

Significance of breast lesion descriptors in the ACR BI-RADS MRI lexicon

In recent years, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has altered the clinical management for women with breast cancer. In March 2007, the American Cancer Society (ACS) issued a new guideline recommending annual MRI screening for high-risk women. This guideline is expected to substantially increase the number of women each year who receive breast MRI. The diagnosis of breast MRI involves the description of morphological and enhancement kinetics features. To standardize the communication language, the Breast Imaging Reporting and Data System (BI-RADS) MRI lexicon was developed by the American College of Radiology (ACR). In this article, the authors will review various appearances of breast lesions on MRI by using the standardized terms of the ACR BI-RADS MRI lexicon. The purpose is to familiarize all medical professionals with the breast MRI lexicon because the use of this imaging modality is rapidly growing in the field of breast disease. By using this common language, a comprehensive analysis of both morphological and kinetic features used in image interpretation will help radiologists and other clinicians to communicate more clearly and consistently. This may, in turn, help physicians and patients to jointly select an appropriate management protocol for each patient's clinical situation.

MRI-guided preoperative wire localization of nonpalpable breast lesions

With the increasing use of magnetic resonance imaging (MRI), the physician is more frequently confronted with nonpalpable breast lesions that are only visible on MRI. In these cases, it is often difficult to obtain adequate material for pathological examination. One of the methods that may be performed is excisional biopsy after MRI-guided wire localization. This study intends to examine the feasibility and added benefit of this method. It appears to be a reliable and useful tool that is, therefore, of additional benefit to surgical practice.

Differentiation of benign from malignant breast disease associated with screening detected microcalcifications using dynamic contrast enhanced magnetic resonance imaging

Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCE-MRI) is an effective diagnostic modality for symptomatic breast disease. However, its role in evaluating clinically occult disease associated with mammographically detected microcalcification remains unclear. Women recalled following screening mammography with microcalcification had DCE-MRI examination of the breast. The data were evaluated subjectively and objectively using both empirical and 2-compartment pharmacokinetic modelling techniques to evaluate signal intensity parameters. Eighty-eight patients aged 50-75 years (median 58) were recruited. Comparing malignant and benign lesions, the mean values in arbitrary units for the enhancement index at 1 min in the most enhancing 9-pixel square +/-1 standard deviation were 0.61+/-0.40 vs. 0.22+/-0.26 p=<0.001 with sensitivity, specificity, PPV, NPV and accuracy of 80.0%, 82.4%, 57.1%, 93.3% and 81.8%, respectively. The corresponding values attained by the radiologist were 75.0%, 89.7%, 68.2%, 92.4% and 86.4%. DCE-MRI is able to differentiate malignant from benign clinically occult lesions associated with microcalcification and may therefore offer an alternative to open surgical biopsy for women with equivocal findings following initial triple assessment for microcalcification in the breast.

Preoperative Magnetic Resonance Imaging-Guided Localization of 131 Breast Lesions With Modified Embolization Coils

OBJECTIVES

The objectives of this study were to assess practicability, outcome, and possible advantages of magnetic resonance imaging (MRI)-guided localizations with modified embolization coils for exclusively MRI-detected suspicious breast lesions.

MATERIALS AND METHODS

We performed 131 MRI-guided preoperative localizations in 105 patients with exclusively MRI-detected breast lesions. Contrast-enhanced, T1-weighted, 3-dimensional gradient echo sequences were used for imaging. Breast fixation and needle guidance were achieved by a perforated plate. Lesion localization was performed with a modified embolization coil. The distance between coil and lesion was measured. Results of specimen radiography and histopathology were analyzed.

RESULTS

Thirty-four of 131 lesions (26%) were malignant. Lesion localization and excision was successful in all patients. The mean distance between the coil and the lesion was 0.5 mm (+/-1.7 mm standard deviation).

CONCLUSIONS

Exact MRI-guided preoperative localization of exclusively MRI-detected breast lesions by using a modified embolization coil is feasible with excellent precision. Advantages over wire localization procedures are the possibility of specimen x-ray and the independence from time and place of operation.

Magnetic Resonance-Guided Biopsies and Localizations of the Breast

OBJECTIVE

The objective of this study was to evaluate the performance of a new commercially available open breast coil and compatible intervention device (Machnet) for magnetic resonance image (MRI)-guided breast interventions.

MATERIALS AND METHODS

Breast lesions detected on MRI were evaluated using MRI-guided core biopsy (n = 20) and/or preoperative wire localization (n = 23) on histologic outcome and accuracy of localization. Time needed to perform a procedure and occurring problems were recorded.

RESULTS

Mean lesion size was <10 mm. Two of 20 lesions could not be biopsied because they were out of range for the device. Biopsies were conclusive in half of the cases; most lesions missed were <10 mm. The average accuracy for needle placement in the localization procedures was less than 2 mm (range, 0-5 mm). The average procedure time was 40 minutes for a biopsy procedure and 33 minutes for an MRI-guided localization.

CONCLUSIONS

Preoperative MRI-guided localizations can be performed quickly and accurately. However, in MRI-guided core biopsies, especially in small lesions, the device does not guarantee conclusive histologic evaluation of the lesion targeted.

A hybrid breast biopsy system combining ultrasound and MRI

System design and initial phantom accuracy results for a novel biopsy system integrating both magnetic resonance (MR) and ultrasound (US) imaging modalities are presented. A phantom experiment was performed to investigate the efficacy of this hybrid guidance biopsy technique in a breast tissue mimicking phantom. A comparison between MR-guided core biopsy verses MR/US-guided core biopsy of phantom targets was realized using a scoring system based on the consistency of the acquired core samples (14 gauge). It was determined that the addition of US to guide needle placement improved the accuracy from an average score of 7.4 out of 10 (MRI guidance alone), to 9.6 (MRI/US guidance) over 21 trials. The average amount of needle tip correction resulting from the additional US information was determined to be 3.7 mm. This correction value is substantial, equal to approximately one radius of the intended targets. Hybrid US/MRI guided biopsy appears to offer a simple means to ensure accurate breast tissue sampling without the need for repeat MRI scans for verification or the need for real-time imaging in open MRI geometries.

Current applications and future direction of MR mammography

Compared with triple assessment for symptomatic and occult breast disease, magnetic resonance mammography (MRM) offers higher sensitivity for the detection of multifocal cancer, which is important in selecting patients appropriately for breast-conserving surgery. It is an ideal tool for the screening of patients with a high risk of breast cancer or where there is axillary disease or nipple discharge and conventional imaging has not revealed the primary focus. Techniques are now available to biopsy lesions only apparent on MRM. MRM can differentiate scar tissue from tumour; therefore, it is useful in patients in which there is possible recurrent disease. Clinical and X-ray mammographic assessment of response to neoadjuvant chemotherapy may be unreliable because of replacement of the tumour with scar tissue. MRM can identify responders and nonresponders with more accuracy. It is the modality of choice for the assessment of breast implants for rupture with accuracy higher than X-ray mammography and ultrasound. Advances in both spatial and temporal resolutions, the imaging sequences employed, pharmacokinetic modelling of contrast uptake, the use of dedicated and now phased-array breast coils, and gadolinium-based contrast agents have all played their part in the advancement of this imaging technique. Despite the limitations of patient compliance, scan-time and cost, this review describes how MRM has become a valuable tool in breast disease, especially in cases of diagnostic uncertainty. However, MRM must make the transition from research institutions into routine clinical practice.

Dedicated double breast coil for magnetic resonance mammography imaging, biopsy, and preoperative localization

RATIONALE AND OBJECTIVES

The aim of this study was to compare the performance of a dedicated double breast coil for MR imaging and intervention with a standard diagnostic double breast coil.

MATERIALS AND METHODS

Signal-to-noise ratios (SNRs) were determined for both coils by using a water phantom. Fourteen patients were examined, 11 underwent preoperative hookwire localization, two were biopsied, and one received diagnostic imaging. Breast images were acquired in three patients with both coils and were visually compared. Harvested specimen from the biopsies and surgeries following hookwire localization were histopathologically evaluated.

RESULTS

SNR was superior with the interventional coil in the posterior (axillary) part of the imaging volume and inferior in the anterior part compared with the standard coil. Anatomic MR breast images were of similar diagnostic quality. For the two biopsy procedures the trocar was correctly placed in front of the suspicious lesion. Hookwires were correctly located inside the lesion in nine patients and in contact with the lesion in one patient. In one patient a 2 mm distance between the lesion and the wire was observed.

CONCLUSIONS

Diagnostic imaging followed by subsequent MR-guided intervention is possible within a single session by using the dedicated interventional coil. The correct final position of the hookwires demonstrates the precision of the MR guided localization procedure.