Contrast-enhanced spectral mammography (CESM) is relatively new diagnostic breast imaging technique that has been utilized in the assessment of breast cancer patients. This technique utilizes a contrast agent to highlight areas of increased vascularization, such as those around and within tumors, using standard mammography equipment (Spotlight Session PD2-11).
At the 2017 San Antonio Breast Cancer Symposium, Bhavika Patel, MD, Department of Radiology, Mayo Clinic Phoenix, and team members presented data from a study in which the use of CESM and MRI was compared in stage I, II, or III breast cancer patients receiving neoadjuvant systemic therapy (NST). Regarding these results, Patel stated, “In the neoadjuvant setting, this study demonstrated that CESM appeared to perform as well as breast MRI in detecting residual cancer.”
Mammography utilizes low-energy X-rays to obtain images of the breast. There is considerable debate among physicians as to its frequency in using it to screen healthy women, as the technique does utilize ionizing radiation for imaging, and there are appreciable rates of misdiagnosis (both false-positives and false-negatives).
MRI technology uses intense magnetic fields and radio waves utilized to generate images using the water molecules present in the patient's body. This mode of imaging utilizes no ionizing radiation; however, it is more expensive and less accessible than mammography. Since strong magnetic fields are involved with MRI, the use of this technique is contraindicated for those patients having pacemakers or cochlear implants.
To enhance the quality of images and thus obtain more relevant diagnostic information, the use of contrast agents has been adopted in many different visualization technologies (e.g., mammography and MRI). In many cancer-based diagnostic applications, visualization is highlighted at the interface of a tumor, where angiogenesis occurs, and there are a larger number of blood vessels with increased porosity.
In X-ray-based visualization techniques, such as CESM, iodine-containing compounds are often utilized. In this study, iohexol was utilized as a contrast agent in CESM-based visualizations.
MRI contrast agents operate upon different principles. MRI contrast agents, which are often gadolinium-containing complexes, frequently shorten the T1 relaxation times for the water-based hydrogen nuclei that are present in the patients' tissues. For this study, dynamic contrast enhanced (DCE) MRI studies were performed using the gadolinium-containing complex gadobutrol as a contrast agent.
Spotlight Session PD2-11
In this single-center study, the use of CESM and breast MRI were compared for 65 breast cancer patients who were undergoing NST from September 2014 to June 2017. This study was limited to stage I, II, or III (non-metastatic) breast cancer patients older than 18 years with a minimum tumor size of T1c.
All patients had both CESM and MRI performed pre- and post-NST. Upon completion of NST and post-NST analyses, surgical resection was performed, and the extracted tumor size was compared to the values obtained on both imaging techniques.
When describing the CESM imaging procedure, Patel noted, “patients received 1.5 mL/kg iohexol contrast agent at a rate of 3 mL/minute while seated; image acquisition was done using standard mammography equipment with special software for contrast-enhanced 2D imaging.
“MRI acquisition was performed using a 3.0 Tesla imaging system with a dedicated 16 channel breast coil while the patient was in the prone position,” she explained. “A DCE MRI image set was acquired in the sagittal orientation using IV-administered gadobutrol as a contrast agent.”
CESM and MRI assessments were performed in a blinded manner by fellowship-trained radiologists with more than 3 months experience at CESM interpretation. There were at least 2 weeks of separation between the post-NST CESM and post-NST MRI interpretations.
When asked to clarify the order in which the procedures described in this study were performed, Patel replied, “The first analyses were the pre-NST CESM and MRI; then, the patients underwent their NST, which was then followed by their post-NST CESM and MRI analyses. After that, surgical resection of their tumors was performed for comparison to their CESM and MRI measurements.”
Sixty-five breast cancer patients (all women) were included in this study. They ranged in age from 30 to 76 years with a mean age of 52.7 years. For 53 of these patients (82%), NST consisted of chemotherapy, while the remaining 12 (18%) utilized endocrine therapy.
The mean post-NST tumor sizes were as follows: CESM—14.6 mm (range: 0-105 mm); MRI—14.2 mm (range: 0-75 mm); post-surgical pathology—19.6 mm (range: 0-100mm). The equivalence test showed that the mean tumor size, as measured by CESM (p=0.009) or MRI (p=0.01), was equivalent to the mean tumor size determined by pathology within the -1 to 1 cm range.
In many metrics, the results for CESM and MRI were very similar; the specificities for both techniques were 95 percent. For CESM, the sensitivity was 66.7 percent, while MRI had a value of 68.9 percent. The positive and negative prediction values obtained for CESM were 96.8 percent and 44.1 percent, respectively; these figures for MRI were 96.9 percent and 42.4 percent.
“The results we obtained demonstrated that, in the neoadjuvant setting, CESM and MRI appeared to perform similarly when determining residual cancer,” Patel noted. “For both CESM and MRI, the rates of false-positives and false-negatives were very comparable, as were other metrics such as sensitivity and specificity.
“MRI is the current gold standard for assessing treatment response in neoadjuvant cases. [However], despite giving very useful information, there are some limitations,” she continued. “The equipment is extremely expensive and, as a consequence, many institutions simply do not have the resources to have an MRI unit. Since there are relatively few of these instruments, the wait times for patients to receive their MRI can be lengthy; additionally, many patients in a rural setting may not even have access to these instruments.”
Regarding the MRI technique, Patel observed, “Many patients may be reluctant to obtain MRIs because of the enclosed nature of many MRI instruments; particularly patients suffering from claustrophobia.
“This often contributes to patient anxiety, and may even be an impediment to some patients obtaining diagnostics using this technique,” Patel continued. “Another significant hindrance to patients is the sometimes prohibitive costs associated with obtaining MR imaging, particularly if the patient's insurance may not cover the costs.”
In highlighting some of the positive attributes of CESM, Patel noted, “The use of CESM is made easier by the fact that the images are acquired using a standard mammography unit with a straightforward software upgrade.
“There are many more institutions that have a mammography unit but not an MRI, thus enabling contrast enhanced diagnostic information more readily available to a larger number of patients,” she added. “The costs for obtaining a mammogram are significantly less, averaging roughly one-sixth the cost for having a complete MRI performed.
“We feel that our findings warrant the undertaking of larger, multicenter prospective studies to validate these results. These additional studies could be expanded in terms of the number of patients included, the number of institutions involved, [and] the number of different brands of mammography units evaluated.
“If the equivalency between these two diagnostic methods is proven, this would potentially allow more breast cancer patients access to effective imaging quicker and less costly than currently may be available,” she concluded.
Richard Simoneaux is a contributing writer.