Benha Medical Journal

ORIGINAL ARTICLE
Year
: 2018  |  Volume : 35  |  Issue : 1  |  Page : 5--12

Contrast-enhanced spectral mammography versus magnetic resonance imaging in the assessment of breast masses


Ahmed F Yousef1, Hamada M Khater1, Lara M Jameel2,  
1 Department of Radiology, Faculty of Medicine, Benha University, Benha, Egypt
2 Department of Radiology, Faculty of Medicine, Al-Anbar University, Ramadi, Iraq

Correspondence Address:
Lara M Jameel
Altejara Street, Benha, 13511
Iraq

Abstract

Background Contrast-enhanced spectral mammography (CESM) has high diagnostic accuracy. It involves the same principles as MRI in terms of the enhancement pattern because of the similar uptake of contrast medium or enhancement. Therefore, the indication should be the same. Aim The aim of the study was to compare CESM and MRI in the assessment of breast masses. Patients and methods This study included 20 patients, and was carried out from December 2016 to May 2017. The age of the patients ranged from 30 to 60 years. Our study was carried out using CESM and breast MRI. Results This study included 20 patients with breast lesions. The age of the patients ranged from 30 to 60 years. All multiple histologically proven lesions were detected by CESM (100%) and MRI (100%), with no significant difference in their site and number in both modalities. Conclusion CESM is useful for the differentiation of local recurrence of post-treatment scarring after breast-conserving therapy and evaluation of residual tumor after treatment, with unknown primary site of malignancy. Recommendations CESM is recommended as the imaging modality of choice in the detection and extension of breast cancer, particularly in problematic cases, or when conservative breast therapy is attempted, but the best correlations with lesion pathology were found in MRI more than CESM, as in MRI, there are the same overlapping patterns of benign and malignant enhancements.



How to cite this article:
Yousef AF, Khater HM, Jameel LM. Contrast-enhanced spectral mammography versus magnetic resonance imaging in the assessment of breast masses.Benha Med J 2018;35:5-12


How to cite this URL:
Yousef AF, Khater HM, Jameel LM. Contrast-enhanced spectral mammography versus magnetic resonance imaging in the assessment of breast masses. Benha Med J [serial online] 2018 [cited 2018 Oct 18 ];35:5-12
Available from: http://www.bmfj.eg.net/text.asp?2018/35/1/5/226412


Full Text



 Introduction



Breast cancer is the most common cancer in women worldwide, with 1.7 million women diagnosed with breast cancer in 2012. Between 2008 and 2012, worldwide breast cancer incidence rates have increased by 20% and mortality rates have increased by 14%. It is important to find an accurate and cost-effective way to detect and diagnose early breast cancers in women across various ages, races, risk levels, economic levels, and geographic settings [1].

In the last few years, new methods have been developed using contrast media to detect breast cancers by tumor angiogenesis using breast MRI systems. Contrast-enhanced breast imaging techniques such as computed tomography (CT) and MRI are used for the detection of angiogenesis by following contrast agent uptake in suspicious breast lesions. Breast MRI is relatively expensive and available primarily in developed countries [2].

Contrast-enhanced breast MRI is currently the most sensitive technique to detect and stage breast cancer. Although appropriate indications for breast MRI are controversial, breast MRI is a viable option in developed countries for high-risk screening and a number of diagnostic indications, including detection and characterization of breast cancer, assessment of local extent of the disease, evaluation of treatment response, and guidance for biopsy and localization. The sensitivity of breast MRI reported in high-risk screening studies ranges from 77 to 100%, higher than those of other imaging modalities [3].

Contrast-enhanced spectral mammography (CESM) has the advantage of enabling acquisition of multiple views of both breasts after a single injection of contrast agent. In CESM, after administration of a contrast agent, each view consists of a rapidly acquired pair of low-energy and high-energy images. The high spatial resolution of the digital detector provides lesion details with ∼10 times the spatial resolution of breast MRI [1].

The feasibility of CESM was reported in 2003 by Lewin et al. using a prototype system [4]. In a group of 26 then a larger clinical study by Dromain et al. [5] that included 80 breast cancers showed that digital mammography plus CESM had higher sensitivity and superior receiver operating characteristic curve areas than mammography alone or mammography plus ultrasound.

The study aimed to compare CESM and MRI in the assessment of breast masses.

 Patients and methods



This study included 20 patients, and was carried out from December 2016 to May 2017. The study was approved by Scientific Research Committee of Benha University An informed consent is taken from all participants. The patients’ age ranged from 30 to 60 years. Our study was carried out using CESM and breast MRI.

Inclusion and exclusion criteria

Inclusion criteria for contrast-enhanced spectral mammography

Any abnormality in mammography examinations, including the following:Mass lesions.Areas of parenchymal distortion.Focal asymmetry.Suspicious micro calcifications.Patients with inconclusive mammography findings because of a heterogeneous dense breast parenchyma.

Exclusion criteria

Patients with renal insufficiency.Patients with allergy to contrast agent.Patients who were pregnant or possibly pregnant.

Mammography system

CESM was performed using a digital mammography unit that had been adapted to obtain two images for each view: a low-energy image (below the k-edge of iodine, 33.2 keV) and a high-energy image (above the k-edge of iodine) at 45–49 kVp.

Contrast-enhanced spectral mammography technique

First, a cannula is inserted into the anticubital fossa on the opposite side of the affected breast. An intravenous injection of iodinated contrast agent (omnipaque 300 mg/ml) was administered before patient positioning and breast compression to the seated patient to avoid interference with the normal vascular dynamics of the breast. Patients received 1–1.5 ml of contrast agent per kilogram of body weight at an injection speed of 3 ml/s, which is the same dose as that used for CT. After the injection, the injector was disconnected from the injector. The cannula was left within the vein to provide a quick intravenous access in case of any allergic reaction.

Patient positioning and performance of spectral mammography were not different from those of conventional mammography. Dual-energy CESM was performed by acquiring a pair of low-energy and high-energy images in quick succession during a single breast compression. Compression was applied for all positions in such a way that it was strong enough to limit breast motion, but at the same time would not reduce blood flow.

A duration of 10 min after the administration of contrast medium injection, a set of bilateral craniocaudal (CC) and mediolateral oblique (MLO) views was acquired. The order of imaging was as follows: the CC view of the unaffected breast, followed by CC and MLO views of the affected breast and then a MLO view of the unaffected breast.

Low-energy images were acquired at peak kilo voltage (kVp) values ranging from 26 to 31, which is below the k-edge of iodine (33.2 keV). High-energy images were acquired at 45–49 kVp, which is above the k-edge of iodine. By subtraction of the two images through appropriate image processing, the visibility of the parenchyma is reduced and contrast-enhanced images are generated.

Image analysis

CESM examination provides a pair of images for image interpretation we used the low-energy image with exposure parameters and appearance.

Lesions that showed enhancement beyond the breast background were considered to be abnormal. The breast imager interpreting the conventional digital mammogram was blinded to the CESM results for that patient. Lesions were categorized on the basis of the Breast Imaging Reporting and Data System (BIRADS). Lesions categorized as BIRADS 3 or BIRADS 2 were considered benign and those categorized as BIRADS 4 or 5 were considered malignant.

Inclusion and exclusion criteria for magnetic resonance imaging

Inclusion criteria for magnetic resonance imaging

The inclusion criteria were the same as those of CESM with the following additional indications:Breast cancer staging.Contralateral breast examination in patients with breast malignancy.Lesion characterization.Monitoring chemotherapy treatment.Evaluation of patients with positive surgical margins for residual disease.Silicone and nonsilicone breast implant evaluation.Evaluation of postoperative scar versus tumor recurrence.Occult breast cancer.Surveillance of high-risk patients.

Exclusion criteria for magnetic resonance imaging

Because of the strength of the field, it is important to inform patients to remove any metal objects before entering into the MRI room, and that the patient informs the clinician/technician of any metal or other implants present in their body. Of particular concern are metallic fragments in the eye (as the eye does not form scar tissue that can hold the fragments in place), pacemakers (which can malfunction if the patient goes near the scanner), and aneurysm clips (as movement may cause tearing of the artery).The MRI scanner can be a problem for individuals with claustrophobia and overweight and obese patients. It should be noted that as new MRI scanners are being developed, the machines per se are becoming smaller and are able to handle larger-sized patients.The machine is very noisy. Earplugs or headphones are used to minimize discomfort to the patient.

Magnetic resonance imaging technique

MRI involves the use of a strong magnetic field to enable detailed visualization of tissues within the body. The superconducting magnet is the most common type of magnet used in MRI. The magnetic field is generated by passing a current through coils of wire, which are bathed in liquid helium at −269.1°C. The main magnet creates a stable magnetic field, whereas three gradient magnets (which are very low strength) are used to create a variable field. These three gradient magnets enable the MRI scanner to image in three different planes (axial, sagittal, and coronal) while the patient remains in one position. In comparison, CT scanning is limited to the axial plane; however, with radiography, patients have to be moved continually to obtain images in different planes. To perform MRI on breast tissue, it is best that a dedicated breast coil is used. This improves comfort for the patient as well as the quality of the images obtained.

The main benefits of MRI are related to the quality and resolution of the images that can be obtained (including the ability to image in different planes) and the fact that the contrast materials used in MRI have a very low incidence of side effects. The radiographer and radiologist’s previous experience with breast MRI has a considerable impact on the quality of the images and their interpretation, and therefore adequate training is required.

Although MRI is generally very safe, there are a number of issues that must be taken into account when considering patients for MRI:

Magnetic resonance imaging protocol

The magnetic field used in MRI is generally of the order of 1.5 T (image acquisition time ∼15–20 min).Scout images (∼1 min).Precontrast (∼5–7 min).T1-weighted no fat suppression (fat/glandular morphology).T2-weighted with fat suppression (bright fluid for cysts).High resolution, three-demintional T1-weighted fat-suppressed gradient echo sequence (precontrast baseline image for identifying enhancing lesions).Postcontrast (3–5 volume acquisitions ∼10 min).

Dynamic multiphase three-demintional T1-weighted fat-suppressed Gradient Echo (GE) sequence (Precontrast and postcontrast images must have identical image parameters to enable subtraction).Analysis:Subtraction of precontrast and postcontrast images (identify enhancing lesions).Dynamic contrast curve evaluation (enhancement pattern assessment).Maximum intensity projection images of subtracted images (vascular bed assessment).

Image interpretation for contrast-enhanced spectral mammography and magnetic resonance imaging

Breast density was recorded and mammograms were analyzed according to the BIRADS lexicon designed by the American College of Radiology.The identified finding in the conventional mammography was assessed, categorized according to the BIRADS classification, described, and measured in its maximum dimensions.We assessed the low-energy images that resembled conventional mammography images to identify non enhancing suspicious clusters of micro calcifications and to evaluate the morphologic features of non enhancing mass lesions.

The presence or absence of contrast enhancement was assessed mainly on the subtraction images and on the basis of contrast enhancement intensity and morphology similar to those described in the BIRADS MRI lexicon developed by the American College of Radiology, except a regular ring pattern, which was considered to be negative in the current study:

(1) The morphological characteristics of the enhancing lesions were assessed and its maximum size was measured. The enhancement was described as follows.

Mass enhancement:Its shape.Margins: well defined, ill defined, or spiculated.Pattern of enhancement: whether homogenous or heterogeneous and uniform or nonuniform ring enhancement.Intensity of enhancement: whether faint, moderate, or intense:Intensity of enhancement: whether faint, moderate, or intense.A mass lesion is described when a three-dimensional space-occupying lesion more than or equal to 5 mm is observed in both mammography views. Nearby lesions more than 5 mm are termed satellite foci of enhancement.Faint and dense enhancement patterns were reported in a subjective manner.Homogeneous, heterogeneous, and ring patterns of contrast uptake were used to describe the internal enhancement characteristics and patterns within enhancing lesions. Homogenous enhancement shows a confluent uniform enhancement within the entire mass. Heterogeneous enhancement is nonuniform, with variable densities. Rim or ring enhancement shows more pronounced enhancement toward the periphery than the center.

 Results



This study included 20 patients with breast lesions. Their ages ranged from 30 to 60 years. They were referred to the National Cancer Institute in Cairo and Tanta. 65% lesions were malignant and 35% were benign. All breast lesions were diagnosed pathologically by means of surgery, excision biopsy, true-cut biopsy, or fine-needle aspiration cytology. We included the dominant or the largest lesion in the measurement of its size in cases with more than one lesion with the same radiological features and BIRADS classification in imaging modality as well as the same pathological diagnosis. A total of 20 lesions were detected in 20 cases. The malignant histopathology results (n=13) were as follows: 9/20 (45%) patients with invasive duct carcinoma (IDC) with or without Ductal Carcinoma In Situ (DCIS), 1/20 (5%) patients with infiltrating lobular carcinoma, 1/20 (5%) patients with mixed IDC and lobular carcinoma (IDC and infiltrating lobular carcinoma), and 2/20 (10%) patients with invasive papillary carcinoma.

The benign lesions (n=7) yielded the following results: 4/20 (20%) patients had fibroadenomas, 1/20 (5%) had abscess, 1\20 (5%) had fibrofatty tissue, and 1/20 (5%) had a scar.

All multiple histologically proven lesions were detected by CESM (100%) and MRI (100%), with no significant difference in their site and number in both modalities.

The reference standard was an abnormality described in all cases as being either benign or malignant. Lesions that were inflammatory lesions were benign.

The total numbers of benign and malignant lesions as well as the final pathological diagnosis for cases are shown in [Table 1]. Of 20 lesions in this study, seven lesions were benign whereas 13 lesions were malignant.{Table 1}

Detailed descriptions of the number and percentage for each pathological breast entity within benign and malignant categories are shown in [Table 8] for benign breast entities and [Table 2] for malignant entities ([Table 3] and [Table 4]).{Table 2}{Table 3}{Table 4}{Table 8}

Imaging findings

CESM enhancement after CESM examination showed a significant heterogeneous enhancement in 10 masses, ring enhancement in three masses, and homogenous enhancement in three cases as shown in [Table 5].{Table 5}

Mass margin by CESM yielded the following results: a well-defined margin in three cases, an ill-defined margin in 12 cases, and spiculated in one case as shown in [Table 6].{Table 6}

Magnetic resonance imaging enhancement

Contrast-enhanced MRI examination yielded the following results: significant heterogeneous enhancement in 14 masses, ring enhancement in three masses, and homogenous enhancement three masses as shown in [Table 7].{Table 7}

Comparison between magnetic resonance imaging and contrast-enhanced spectral mammography in benign lesions

Comparison between CEDM and DCE-MRI in correct diagnosis among pathologically proven seven benign lesions are shown in [Table 8].

Comparison between CESM and MRI in correct diagnosis among pathologically proven 13 malignant lesions are shown in [Table 9].{Table 9}

Estimation of the size was performed at the maximum diameter of the lesion for both modalities (CESM and MRI) and correlated with the pathological size.

The estimation of size was performed for 20 lesions, 13 malignant, and seven benign. We observed in our study that there was no significant difference in the size assessment of the lesions in both modalities (CESM and MRI) compared with pathology; the best correlation with pathology was found for MRI ([Figure 1],[Figure 2],[Figure 3],[Figure 4]).{Figure 1}{Figure 2}{Figure 3}{Figure 4}

 Discussion



Within the same breast compression, low-energy exposure results in a low-dose, high-resolution mammogram, followed a second later by high-energy exposure. This provides a contrast medium enhancement of abnormal breast lesions. These two images are taken immediately after exposure; meanwhile, the automatic direct digital subtraction of the two images is presented immediately on the monitor. The enhancement pattern of the CESM follows the rules of contrast-enhanced MRI. Compared with MRI, CESM show better resolution of a mammography over the MRI (with better appearance of micro calcifications and its details), with no motion because both images are obtained in one breast compression of a couple of seconds. The equipment needed for this examination is much cheaper with the use of a well known and cheaper iodinated contrast medium. The procedure is fast, uncomplicated, and similar to routine mammography, which includes two views to study both breasts. The procedure takes less time: around 4 min for a capable technician. There are no limitations for overweight patients, or patients with a cardiac pace maker, a vascular stent, a metallic prosthesis, or old magnetic devices and clips.

We present a clear case of a malignancy not shown by mammography, but identified positively with CESM. We also present a highly suspected malignancy. By mammography, which was negative by CESM, breast mass is not commonly demonstrable in mammographic examinations of extremely dense breasts. Although diagnosis of cancer breast by digital mammography is highly suspicious, the presence of malignancy can mostly be excluded. The enhancement patterns resemble MRI, believed to involve the same principle of tumor vascularization and perfusion abnormality of abnormal cells.

Recently, the FDA approved the use of MRI in dense breast examinations, which should be replaced by CESM. There are also unwanted side effects of iodinated contrast medium, although this is uncommon in healthy women. Thus, we suggest that CESM should be performed when there is an indication, and not as a routine modality.

The results of this study are comparable with the findings of Houssami et al. [6], who confirmed that breast MRI is extremely sensitive with limited specificity, leading to additional workup and biopsies with false-positive results. In this study, CESM showed lower sensitivity for breast cancer detection and higher specificity compared with MRI [6].

 Conclusion



CESM provides high diagnostic accuracy. It involves the same principles as MRI in terms of the enhancement pattern because of the similar uptake of contrast medium or enhancement. Therefore, the indication should be the same.

In comparison with MRI, CESM can detect micro calcifications easily, and there are no limitations as with MRI in terms of the ferromagnetic effect and machine design.

CESM is much more cost-effective than MRI because of the lower cost of equipment, contrast medium, and less time consuming than with the use of routine mammography views. The average time taken in the mammography room is around 4–6 min in a routine study. Thus, the patient flow is considerably better.

CESM should be the imaging modality of choice in the detection and extension of breast cancer, particularly in problematic cases, or when conservative breast therapy is attempted but with pathological examination of the lesions, the best correlation was found with MRI than CESM, as in MRI there were the same overlapping patterns of benign and malignant enhancements.

CESM is useful for the differentiation of local recurrence of post-treatment scarring after breast-conserving therapy and evaluation of residual tumor after treatment, with unknown primary site of malignancy.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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