Diagnostic value of qualitative and quantitative enhancement parameters on contrast-enhanced mammography

PURPOSE: To determine whether qualitative and quantitative enhancement parameters obtained from contrast-enhanced mammography (CEM) can be used in predicting malignancy. METHODS: After review board approval, consecutive 136 suspicious lesions with definite diagnosis were retrospectively analyzed on CEM. Acquisition was routinely started with craniocaudal view and ended with mediolateral oblique view of the affected breast. Lesion conspicuity (low, moderate, high), internal enhancement pattern (homogeneous, heterogeneous, rim), contrast-to-noise ratio (CNR), percentage of signal difference (PSD) and relative enhancement from early to late view were analyzed. PSD and relative enhancements were used to determine patterns of descending, steady or ascending enhancements. Receiver operating characteristic analysis, Cohen's kappa statistics and Spearman correlation tests were used. RESULTS: There were 29 benign and 107 malignant lesions. 64% of the malignant lesions exhibited high conspicuity compared to 14% of the benign lesions (P < 0.001). CNR values were higher in malignant lesions compared to benign ones (P ≤ 0.004). CNR from early view yielded 82% sensitivity, 72% specificity and PSD yielded 79% sensitivity, 65% specificity. Descending pattern and rim enhancement observed in 44% and 21% of breast cancers, respectively, and both provided 96% positive predictive value for malignancy. CONCLUSION: Diagnostic accuracy of quantitative parameters was higher than that of qualitative parameters. High CNR, rim enhancement, and descending pattern were features commonly seen in malignant lesions, while low CNR, homogeneous enhancement, and ascending pattern were commonly seen in benign lesions.

Evaluation of the height of the corpus callosum body region in fetal meningomyelocele malformation.

PURPOSE: To investigate height of the corpus callosum (CC) in order to describe the corpus callosum anomalies in fetuses with meningomyelocele (MMC) and compare these findings with the corpus callosum of healthy fetuses. METHODS: In this study, fetal MRI examinations were performed on 44 fetal MMC malformation cases. As the control group, 34 fetal MRI examinations, which were anatomically normal, were evaluated retrospectively. In the study group, lateral ventricle diameter, the level and diameter of the MMC defect, and CC height were measured. In the control group, CC height and lateral ventricular diameter were measured. RESULTS: The mean CC body height was 1.36 mm in the study group, and 2.48 mm in the control group. The height of the CC body region of the study population was inclined to be thinner compared with the control population (p<0.001). CONCLUSIONS: The fact that the height of the CC body region was found to be thinner in fetal MRI in cases of MMC compared with normal fetuses suggests that various callosal anomalies are uncertain, investigation of additional callosal anomalies may be beneficial in the decision for the continuation of pregnancy, and termination or intrauterine surgery in cases with MMC. Further large case group studies are needed.

High-resolution diffusion-weighted imaging compared with conventional diffusion-weighted imaging and dynamic contrast-enhanced magnetic resonance imaging with regard to image quality and assessment of breast cancer morphology

PURPOSE: To evaluate the image quality and tumor morphology depiction ability of high resolution (HR) diffusion- weighted imaging (f-DWI) in comparison to conventional DWI (c-DWI) and dynamic contrast- enhanced magnetic resonance imaging (DCE-MRI) in the primary breast cancer setting. METHODS: The f-DWI, c-DWI, and DCE-MRIs of 160 malignant breast masses were evaluated retrospectively by two independent radiologists. Data on image quality [sharpness, distortion, and perceived signalto- noise ratio (SNR)], apparent diffusion coefficient (ADC) value, lesion size, and tumor morphology (shape, margin, and internal pattern) obtained on f-DWI, c-DWI, and DCE-MRI were compared. Consistency between the readers and imaging methods for morphological parameters was analyzed. RESULTS: The ADC values measured on f-DWI were significantly lower than those measured on c-DWI for both readers (P < 0.001 for each), whereas mean lesion size was significantly larger in c-DWI than in f-DWI and DCE-MRI for both readers (P < 0.001 for each). Higher consistency values were obtained for f-DWI compared with c-DWI when correlated with DCE-MRI for each morphological parameter. The least distorted images were obtained using DCE-MRI compared with c-DWI and f-DWI for both readers, whereas the highest distortion scores were obtained using c-DWI. Sharpness and perceived SNR scores were rated as significantly higher for f-DWI and DCE-MRI images compared with c-DWI by both readers (P < 0.001 for all). The concordance between c-DWI and DCE-MRI was fair to slight (κ = 0.15 to 0.41), whereas concordance between f-DWI and DCE-MRI was significantly better (κ = 0.68 to 0.87) for each reader and for all morphological parameters (P < 0.001). The highest concordance between the readers was achieved in margin assessment (κ = 0.87 to 0.89) regardless of the MRI method, followed by shape and internal pattern parameters (κ = 0.63 to 0.79). CONCLUSION: The results demonstrated that f-DWI produces higher-quality images than c-DWI, enabling the morphological features to be identified in similar detail to that offered by HR DCE-MRI. Accordingly, f-DWI, as a method that highly correlates with DCE in determining the morphological characteristics of breast cancers, seems to have potential in the evaluation of breast tumors in patients for whom the use of contrast media is contraindicated.

Outcomes of high-risk breast lesions diagnosed using image-guided core needle biopsy: results from a multicenter retrospective study.

PURPOSE: The clinical management of high-risk lesions using image-guided biopsy is challenging. This study aimed to evaluate the rates at which such lesions were upgraded to malignancy and identify possible predictive factors for upgrading high-risk lesions. METHODS: This retrospective multicenter analysis included 1.343 patients diagnosed with high-risk lesions using an image-guided core needle or vacuum-assisted biopsy (VAB). Only patients managed using an excisional biopsy or with at least one year of documented radiological follow-up were included. For each, the Breast Imaging Reporting and Data System (BI-RADS) category, number of samples, needle thickness, and lesion size were correlated with malignancy upgrade rates in different histologic subtypes. Pearson's chi-squared test, the Fisher-Freeman-Halton test, and Fisher's exact test were used for the statistical analyses. RESULTS: The overall upgrade rate was 20.6%, with the highest rates in the subtypes of intraductal papilloma (IP) with atypia (44.7%; 55/123), followed by atypical ductal hyperplasia (ADH) (38.4%; 144/375), lobular neoplasia (LN) (12.7%; 7/55), papilloma without atypia (9.4%; 58/611), flat epithelial atypia (FEA) (8.7%; 10/114), and radial scars (RSs) (4.6%; 3/65). There was a significant relationship between the upgrade rate and BI-RADS category, number of samples, and lesion size Lesion size was the most predictive factor for an upgrade in all subtypes. CONCLUSION: ADH and atypical IP showed considerable upgrade rates to malignancy, requiring surgical excision. The LN, IP without atypia, pure FEA, and RS subtypes showed lower malignancy rates when the BI-RADS category was lower and in smaller lesions that had been adequately sampled using VAB. After being discussed in a multidisciplinary meeting, these cases could be managed with follow-up instead of excision.

The validity and clinical utility of axillary ultrasonography-guided fine needle aspiration biopsy in detection of nodal metastasis in early-stage breast cancer patients: a retrospective single-center experience.

BACKGROUND: Assessing the validity and clinical utility of axillary ultrasonography (AUS)-guided fine needle aspiration biopsy (FNAB) in detection of nodal metastasis during preoperative axillary investigation in comparison to the histopathologic diagnosis in early-stage breast cancer. METHODS: A total of 279 operated primary breast cancer patients (age: 55.3 ± 12.8, ranged 17-90 years) were included. Data on AUS findings at the time of initial diagnosis (first look AUS), second-look AUS findings performed by the breast radiologist during breast biopsy procedure and the AUS-guided FNAB findings were evaluated with respect to the final histopathology report obtained through axillary surgery via sentinel lymph node biopsy (SLNB) and/or axillary lymph node dissection (ALND). The diagnostic performance of each method in detecting metastatic ALNs were compared in terms of sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV). RESULTS: The sensitivity, specificity, and accuracy of the first look AUS in detecting nodal metastasis were 64.56%, 86.78%, and 74.19% while the PPV and NPV were 86.44% and 65.22%, respectively. The sensitivity, specificity, and accuracy of the second-look AUS were 70.25%, 87.60%, and 77.78%, while PPV and NPV were 88.10% and 69.28%, respectively. The sensitivity, specificity, and accuracy of the second-look AUS guided FNAB were 89.19%, 73.33%, and 87.30%, while the PPV and NPV were 96.12% and 47.83%, respectively. The consideration of second-look AUS and finding of nodal metastasis in FNAB was associated with significantly higher likelihood of ALND (55.4% vs. 44.6%, p < 0.001) and lower likelihood of SLNB (34.7% vs. 65.3%, p < 0.001) compared to consideration of nonmetastatic ALN status. In 23 (22.3%) patients with positive findings on AUS-guided FNAB, SLNB was applied; 21 had positive results after surgical dissection, indicating that nearly 20% of patients had unnecessary SLNB. DISCUSSION: US-guided FNAB of suspicious ALNs is a simple, minimally invasive, and highly effective method for preoperative axillary staging in patients with invasive breast cancer avoiding the more invasive method SLNB and it enables the surgeon to proceed directly to ALND in positive cases.

Qualitative characterization of breast tumors with diffusion-weighted imaging has comparable accuracy to quantitative analysis.

PURPOSE: To evaluate the applicability and accuracy of a new qualitative diffusion-weighted imaging (DWI) assessment method in the characterization of breast tumors compared to quantitative ADC measurement and dynamic contrast enhanced magnetic resonance imaging (DCE-MRI). MATERIALS AND METHODS: After review board approval, MRIs of 216 consecutive women with final diagnoses (131 malignant, 85 benign) were retrospectively analyzed. Two radiologists independently scored DWI and dynamic contrast-enhanced MRI (DCE-MRI) according to malignancy probability. Qualitative assessments were performed by combined analysis of tumor morphology and diffusion signal. Quantitative data was obtained from apparent diffusion coefficient (ADC) measurements. Lastly, descriptive DWI features were evaluated and recorded. Cohen's kappa, receiver operating characteristic and multivariate analyzes were applied. RESULTS: Of malignant tumors, 97% were visible on DWI. Qualitative and quantitative DWI assessments provided comparable sensitivities of 89-94% and 88-92% and specificities of 51-61% and 59-67%, respectively. There was no statistical difference between the accuracies of qualitative and quantitative DWI (p ≥ 0.105). Best diagnostic values were obtained with DCE-MRI (sensitivity, 99-100%; specificity, 69-71%). Inter-reader agreement was moderate (kappa = 0.597) for qualitative DWI and substantial (kappa = 0.689) for DCE-MRI (p < 0.001). Agreement between qualitative DWI and DCE-MRI scores was moderate (kappa = 0.536 and 0.442). Visual diffusion signal, mass margin and shape were the most predictive features of malignancy on multivariate analysis of qualitative assessment. CONCLUSION: Qualitative characterization of breast tumors on DWI has comparable accuracy to quantitative ADC analysis. This method might be used to make DWI more widely available with eliminating the need to a predetermined ADC threshold in tumor characterization. However, lower accuracy and inter-reader agreement of it compared to DCE-MRI should be considered.

Diagnostic value of 3D power Doppler ultrasound in the characterization of thyroid nodules

Background/aim: This study aimed to evaluate the diagnostic value of vascular indices obtained using 3D power Doppler ultrasound (3D PDUS) in differentiation of benign and malignant thyroid nodules. Materials and methods: Sixty-seven patients (56 female, 11 male, mean age 44.6) with 81 thyroid nodules exhibiting mixed (peripheral and central) vascularization patterns, with the largest diameter between 10 and 30 mm, were prospectively evaluated using 3D PDUS. Nodule volume, vascularization index (VI), flow index (FI), and vascularization flow index (VFI) were calculated using the Virtual Organ Computer-aided Analysis (VOCAL) software, and these indices were then compared with regard to the cytohistopathology-based diagnosis. The optimum cutoff values for the differentiation of benign and malignant nodules were identified, and diagnostic efficacy was calculated using receiver operating characteristic (ROC) analysis. Results: Fifty-six of the 81 nodules included in this study were diagnosed as benign and 25 as malignant. Vascular indices in malignant nodules were significantly higher than those in benign nodules (P < 0.05). In benign nodules, the mean VI was 11.61 ± 6.88, mean FI was 39.75 ± 3.93, and mean VFI was 4.82 ± 2.94, compared to 18.64 ± 12.81, 41.82 ± 4.43, and 8.17 ± 6.37, respectively, in malignant nodules. The area under the curves (AUCs) was calculated as 0.68, 0.61, and 0.67 for VI, FI, and VFI, respectively. At optimal cutoff values of 10.2 for VI, 40.8 for FI, and 5.5 for VFI, the sensitivity and specificity were 72%/55.4%, 68%/57.1%, and 68%/67.9%, respectively. Conclusion: 3D PDUS can be useful in the characterization of thyroid nodules.

Neurocognitive Functions in Infants with Malnutrition; Relation with Long-chain Polyunsaturated Fatty Acids, Micronutrients Levels and Magnetic Resonance Spectroscopy.

PURPOSE: Malnutrition may influence neurocognitive development in children by directly affecting the brain structural development, or indirectly by affecting the children's cognition experience. Malnutrition alters the cell numbers, cell migration, synaptogenesis, and neurotransmission due to inadequate availability of necessary micronutrients to support cell growth. We aimed to analyze neurocognitive development in infants with malnutrition and its association with long chain polyunsaturated fatty acids (LC-PUFA), micronutrients levels and magnetic resonance spectroscopy (MRS) findings. METHODS: The study included two groups; group 1, infants with malnutrition (n=24), group 2; healthy infants (n=21). Peripheral blood was obtained from the participants for studying micronutrients and LC-PUFA levels. The neurocognitive development was analyzed by the use of an Ankara Developmental Screening Inventory test. MRS were performed on all infants. RESULTS: All parameters of neurocognitive development and serum calcium (9.6±0.9 mg/dL vs. 10.4±0.3 mg/dL, p<0.05) and magnesium (2.02±0.27 mg/dL vs. 2.2±0.14 mg/dL, p<0.05) levels were noted as being low in infants with marked malnutrition. No difference was found in LC-PUFA levels between healthy and malnourished infants. Thalamic choline/creatine levels were significantly high in infants with malnutrition (1.33±0.22 vs. 1.18±0.22, p<0.05). Total neurocognitive development in infants was positively correlated with serum calcium levels (p<0.05, r=0.381). CONCLUSION: Calcium supplementation may improve neurocognitive development in malnourished infants.

Value of tomography in detecting breast masses and discriminating malign and benign lesions.

OBJECTIVES: The main purpose of the present study was to determine the effectivity of computerized tomography (CT) in detecting breast masses and discriminating masses as malignant or benign. MATERIAL AND METHODS: After having received the institutional local ethics committee approval, an experienced radiologist who did not participate in the study created a patient pool by searching our health center's Pathology department database between 2010 and 2018. The group created consisted of dense and non-dense breast types equally and included approximately similar percentages of benign and malignant breast mass sizes. Finally, 70 subjects were included: 30 females with definite malign, 20 with definite benign breast masses, and 20 without any breast pathology based on mammography and ultrasonography results, who were considered as the control group. Three experienced Radiologists (R1, R2, R3) who were not aware of the final diagnosis evaluated all images independently. Radiologist performance was assessed by calculating the area under the receiver operating characteristic curve (AUC) and interobserver reliability values were estimated by intraclass correlation coefficient (ICC) analysis. RESULTS: The diagnostic accuracy suitability of CT according to BI-RADS scores for R1, R2 and R3 were found as p <0.001, p <0.001 and p <0.001, respectively. There were significant interobserver reliability rates between all investigators (p= 0.0001). CONCLUSION: CT may be used as a valuable diagnostic tool in discriminating breast masses with further training in widely varying appearances of normal breast tissues leading to false positive findings.

Assessment of breast mass morphology with diffusion-weighted MRI: Beyond apparent diffusion coefficient.

BACKGROUND: Diffusion-weighted imaging (DWI) is a noncontrast-enhanced MRI technique. There are new promising studies on the use of DWI as a part of the enhanced or unenhanced abbreviated breast MRI protocols. PURPOSE: To evaluate the ability of breast DWI in the assessment of mass morphology and determine the contribution of this morphologic evaluation in their characterization. STUDY TYPE: Retrospective. POPULATION: In all, 213 consecutive women were breast MR imaged and had a later confirmed diagnosis. FIELD STRENGTH/SEQUENCE: Breast dynamic contrast-enhanced-MRI (DCE-MRI) and DWI at 1.5T. ASSESSMENT: After Institutional Review Board approval, two radiologists first independently, and later in consensus, evaluated the visibility and morphology of the 143 malignant, 70 benign masses on DWI and DCE-MRI in separate sessions, blindly. Shape, margin, and internal pattern of the masses were evaluated according to BI-RADS lexicon. Apparent diffusion coefficient (ADC) and tumor size were measured by one radiologist. STATISTICAL TESTS: Consistency between imaging methods and readers was evaluated with Cohen's kappa statistics. Multivariate analysis was applied to find the best predictors of malignancy. RESULTS: Tumor visibility on DWI was high to moderate in at least 88% of cases. Consistency between DWI and DCE-MRI was substantial (kappa ≥0.757) for shape and margin and moderate (kappa = 0.505) for internal pattern. Interobserver agreement was substantial to moderate for all morphologic parameters (kappa ≥0.596). Morphology evaluated on DWI provided 83-84% accuracy in discriminating malignant from benign masses. ADC alone provided 90-91% accuracy. Both morphologic parameters and ADC were significantly associated with malignancy on multivariate analysis and provided 91-93% accuracy. DATA CONCLUSION: DWI might be used not only for ADC evaluation but also for the morphological evaluation of breast masses to characterize them. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:1668-1677.

A Case of Wernicke Encephalopathy Developing After Ileal Bypass Surgery.

Wernicke encephalopathy is an acute neurological problem resulting from thiamine deficiency and manifesting with mental confusion, oculomotor dysfunction, and ataxia. It is associated with alcohol dependence in adults. Preparatory factors include hyperemesis gravidarum, prolonged diarrhea, prolonged parental nutrition without vitamin support, absorption disorders, anorexia, cancer, and chemotherapy. Failure to consider the clinical findings and preparatory factors of this disease, which is rare in children, can delay diagnosis. This report describes a case of Wernicke encephalopathy developing in a patient with brid ileus and receiving total parenteral nutrition after partial ileal bypass surgery. The patient's clinical and cranial magnetic resonance findings were compatible with Wernicke encephalopathy. Although these are not widespread, typical ocular findings for Wernicke encephalopathy were present. Dramatic improvements were observed in clinical, ocular, and cranial magnetic resonance findings after treatment.

Leukoencephalopathy with thalamus and brainstem involvement and high lactate caused by novel mutations in the EARS2 gene in two siblings.

Leukoencephalopathy with thalamus and brainstem involvement, and high lactate (LTBL) is a recently identified disease related to mutations in the EARS2 gene encoding glutamyl-tRNA synthetase. We report clinical and radiological findings for two siblings with new pathogenic mutations in the EARS2 gene. Both patients showed symptoms of mild-type disease, but there were clinical differences between the two siblings. While the older brother had hypotonia and delayed developmental milestones, the younger brother had seizures and spasticity in the lower extremities. Brain magnetic resonance imaging (MRI) findings were quite similar for the two siblings. MRI findings were specific to LTBL. MRI lesions of the older sibling had regressed over time. Clinical and radiological improvement, as in the previously reported patients with LTBL, may be an important clue for diagnosis.

Role of 3D power Doppler ultrasound in the further characterization of suspicious breast masses.

PURPOSE: To investigate effectiveness of vascular indices obtained with 3D power Doppler ultrasound in the further characterization of breast masses and prevention of unnecessary biopsies. MATERIALS AND METHODS: Between April 2013 and March 2014, 109 patients (age range, 17-85 years; mean age, 47 years) with 117 radiologically or clinically suspicious breast masses were prospectively evaluated with 3DPDUS before biopsy. Mass volume (MV), vascularization index (VI), flow index (FI) and vascularization flow index (VFI) were calculated using Virtual Organ Computer-aided Analysis (VOCAL) software and they were correlated with the final diagnosis. Cutoff values of vascular indices were determinated and diagnostic efficacy was calculated with receiver operating curve (ROC) analysis. RESULTS: All vascular indices, age of patients and tumor volume were significantly lower in benign masses compared with malignant ones (p<0.001). AUCs were 0.872, 0.867 and 0.789 for VI, VFI and FI, respectively. The diagnostic efficacy of VI (for cutoff 1.1; 83% sensitivity, 82% specificity and 82% accuracy) and VFI (for cutoff 0.4; 80% sensitivity, 83% specificity and 80% accuracy) were significantly higher than FI (for cutoff 33,9; 73% sensitivity, 69% specificity and 71% accuracy). It was found that with the use of vascular indices of 3DPDUS in the further characterization of suspicious breast masses between 24% to 37% of unnecessary biopsies could have been avoided. CONCLUSION: The vascular indices obtained with 3DPDUS seem reliable in the further characterization of suspicious breast masses and might be used to decrease unnecessary biopsies.

Umbilical venous catheter complications in newborns: a 6-year single-center experience.

OBJECTIVE: Umbilical venous catheter (UVC) insertion is frequently performed in critically ill neonates. Various mild or serious complications of umbilical venous catheterization can be observed associated with this procedure. In this study, newborns that have undergone UVC and developed complications were evaluated. METHODS: This retrospective observational study was carried out in newborns that have undergone UVC and developed complications were evaluated between June 2008 and November 2014. RESULTS: Umbilical venous catheter were inserted to 974 (22.4%) newborn and followed for 7402/catheter days. UVC-related complications developed at 198 patients (20.3%). The most common UVC-related complications were malposition (n = 189), catheter-related bloodstream infection (n = 6) and remnant of catheter in the umbilicus (n = 3), respectively. Remnant of catheter in the umbilicus was removed by pediatric surgeon. Except one patient, all patients were discharged. CONCLUSION: Although UVC is a common and easy vascular access, this process is not without complications. UVC may be inappropriate position because the catheter is inserted by the pediatrician without imaging guidance and may occasionally be associated with complications. Inappropriate positioning of the catheter may observe during the follow-up and maintained care. Therefore, newborns particularly in premature and very low birth-weight newborn should be followed in terms of catheter complications during insertion, following and just after removing of the catheter.

Is Sinusitis Innocent?--Unilateral Subdural Empyema in an Immunocompetent Child.

Subdural empyema related to Streptococcus constellatus is extremely rare in an immunocompetent child, and also there is no reported case along with Staphylococcus lugdunensis infection. Although Streptococcus constellatus has been determined as a co-pathogen with anerobic bacteria in many infections, it has not been reported in combination with Staphylococcus lugdunensis. The authors describe a case of previously healthy 16-y-old child with unilateral subdural empyema due to these bacteria. Sinusitis was the only predisposing factor in the index case. The authors propose that some cases of culture-negative intracranial infections may be due to these infectious agents. Therefore, these agents should be considered as causes of intracranial infection in persistent complaints such as fever and headache after sinusitis in children. It is important to treat them with effective antibiotics and early surgical intervention for favorable outcome, because fatal cases were reported due to Streptococcus constellatus infections.

Can unenhanced breast MRI be used to decrease negative biopsy rates?

PURPOSE: We aimed to determine whether low-risk breast masses can be effectively managed with unenhanced magnetic resonance imaging (MRI) combining T2-weighted sequences with diffusion-weighted imaging (DWI) instead of immediate biopsy to decrease negative biopsy rates. METHODS: After institutional review board and patient approvals, 141 consecutive women with 156 low-risk breast masses, who underwent unenhanced MRI and later on received a final diagnosis, were included in the study. There were 72 BI-RADS 3 masses in women with relative risk factors and 84 BI-RADS 4A masses, all referred for biopsy. Apparent diffusion coefficient (ADC) cutoff was 0.90×10-3 mm2/s. According to ADC values and T2-weighted imaging characteristics, masses were classified as either malignant or benign. Unenhanced MRI results were compared with final diagnoses obtained by histopathology or imaging surveillance, and diagnostic values were calculated. RESULTS: Of 156 masses, 112 underwent biopsy. Four malignancies were diagnosed, three of which having ADC values lower than the cutoff. In women who rejected the biopsy, masses were stable during a follow-up of at least two years (n=44). MRI revealed 91% specificity and 99% negative predictive value (NPV) for detection of breast cancer. CONCLUSION: Combination of T2-weighted imaging with DWI is a feasible method to further characterize breast masses with a low probability of malignancy. With the use of unenhanced MRI instead of immediate biopsy, it might be possible to decrease negative biopsy rates of low-risk breast masses.