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Dynamic Breast MR Imaging: Are Signal Intensity Time Course Data Useful for Differential Diagnosis of Enhancing Lesions?¹

¹ From the Departments of Radiology (C.K.K., P.M., S.K., C.L., H.H.S.) and Pathology (E.W.), University of Bonn, Sigmund-Freud-Str 25, D-53105 Bonn, Germany, and Philips Medical Systems, Hamburg, Germany (J.G.). From the 1996 RSNA scientific assembly. Received March 2, 1998; revision requested May 5; final revision received August 5; accepted October 7. Address reprint requests to C.K.K.

View larger version (19K): [in a new window]   Figure 1. Schematic drawing of the time–signal intensity curve types. Type I corresponds to a straight (Ia) or curved (Ib) line; enhancement continues over the entire dynamic study. Type II is a plateau curve with a sharp bend after the initial upstroke. Type III is a washout time course ([SIc - SI]/SI).

View larger version (14K): [in a new window]   Figure 2. Bar graph shows the mean early-phase enhancement rates in breast cancers, benign solid tumors, and fibrocystic changes (N/PFC) ± SD (error bars). Enhancement rates are calculated for the 1st postcontrast minute.

View larger version (25K): [in a new window]   Figure 3. Bar graph shows the distribution of time–signal intensity curve types in malignant lesions, benign solid lesions, and fibrocystic changes (N/PFC).

View larger version (12K): [in a new window]   Figure 4. Bar graph shows the prevalence of benign (black bars) and malignant (white bars) lesions for the three different signal intensity time courses.

View larger version (147K): [in a new window]   Figure 5a. Breast MR images acquired in a 55-year-old patient with a palpable mass in the left upper outer quadrant. The mass had been rated as probably benign on the basis of mammographic and US findings. (a) Axial maximum intensity projection MR image from an early postcontrast subtracted data set of the diagnostic breast MR imaging study (220/4.5; flip angle, 80°). The maximum intensity projection image depicts two lesions (arrows): the expected palpable mass (P) and a nonpalpable, incidental lesion (I) in the left breast. (b) Early postcontrast and (c) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) show the palpable mass (P). (d) Time–signal intensity curve of the palpable mass shows a type I time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The palpable mass visible in b–d exhibits a suggestively strong early-phase enhancement, but it is well circumscribed, has a lobulated appearance, and reveals internal septations, which are all findings consistent with fibroadenoma. d further supports the diagnosis of a fibroadenoma. The signal intensity time course corresponds to a type Ib curve. (e) Early postcontrast and (f) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) obtained several sections cephalad of the palpable mass in b–d show the incidental lesion (arrow). (g) Time–signal intensity curve of the incidental lesion shows a type III time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The small, incidental, nonpalpable lesion visible in e–g shows the same rapid enhancement as the lesion visible in b–d. Also, it is well circumscribed and enhances homogeneously. However, it has a type III (washout) curve, which prompted the prospective diagnosis of an occult breast cancer, together with a fibroadenoma, in the same breast. Because the incidental lesion visible in e–g remained invisible at mammography (including spot compression) and at directed high-frequency breast US, excisional biopsy was performed after MR-guided stereotactic needle localization. Histologic confirmation of a 6-mm ductal invasive breast cancer pT1bN0M0 was obtained for the incidental lesion visible in e–g, and confirmation of a myxoid fibroadenoma was obtained for the palpable lesion visible in b–d.

View larger version (169K): [in a new window]   Figure 5b. Breast MR images acquired in a 55-year-old patient with a palpable mass in the left upper outer quadrant. The mass had been rated as probably benign on the basis of mammographic and US findings. (a) Axial maximum intensity projection MR image from an early postcontrast subtracted data set of the diagnostic breast MR imaging study (220/4.5; flip angle, 80°). The maximum intensity projection image depicts two lesions (arrows): the expected palpable mass (P) and a nonpalpable, incidental lesion (I) in the left breast. (b) Early postcontrast and (c) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) show the palpable mass (P). (d) Time–signal intensity curve of the palpable mass shows a type I time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The palpable mass visible in b–d exhibits a suggestively strong early-phase enhancement, but it is well circumscribed, has a lobulated appearance, and reveals internal septations, which are all findings consistent with fibroadenoma. d further supports the diagnosis of a fibroadenoma. The signal intensity time course corresponds to a type Ib curve. (e) Early postcontrast and (f) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) obtained several sections cephalad of the palpable mass in b–d show the incidental lesion (arrow). (g) Time–signal intensity curve of the incidental lesion shows a type III time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The small, incidental, nonpalpable lesion visible in e–g shows the same rapid enhancement as the lesion visible in b–d. Also, it is well circumscribed and enhances homogeneously. However, it has a type III (washout) curve, which prompted the prospective diagnosis of an occult breast cancer, together with a fibroadenoma, in the same breast. Because the incidental lesion visible in e–g remained invisible at mammography (including spot compression) and at directed high-frequency breast US, excisional biopsy was performed after MR-guided stereotactic needle localization. Histologic confirmation of a 6-mm ductal invasive breast cancer pT1bN0M0 was obtained for the incidental lesion visible in e–g, and confirmation of a myxoid fibroadenoma was obtained for the palpable lesion visible in b–d.

View larger version (158K): [in a new window]   Figure 5c. Breast MR images acquired in a 55-year-old patient with a palpable mass in the left upper outer quadrant. The mass had been rated as probably benign on the basis of mammographic and US findings. (a) Axial maximum intensity projection MR image from an early postcontrast subtracted data set of the diagnostic breast MR imaging study (220/4.5; flip angle, 80°). The maximum intensity projection image depicts two lesions (arrows): the expected palpable mass (P) and a nonpalpable, incidental lesion (I) in the left breast. (b) Early postcontrast and (c) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) show the palpable mass (P). (d) Time–signal intensity curve of the palpable mass shows a type I time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The palpable mass visible in b–d exhibits a suggestively strong early-phase enhancement, but it is well circumscribed, has a lobulated appearance, and reveals internal septations, which are all findings consistent with fibroadenoma. d further supports the diagnosis of a fibroadenoma. The signal intensity time course corresponds to a type Ib curve. (e) Early postcontrast and (f) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) obtained several sections cephalad of the palpable mass in b–d show the incidental lesion (arrow). (g) Time–signal intensity curve of the incidental lesion shows a type III time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The small, incidental, nonpalpable lesion visible in e–g shows the same rapid enhancement as the lesion visible in b–d. Also, it is well circumscribed and enhances homogeneously. However, it has a type III (washout) curve, which prompted the prospective diagnosis of an occult breast cancer, together with a fibroadenoma, in the same breast. Because the incidental lesion visible in e–g remained invisible at mammography (including spot compression) and at directed high-frequency breast US, excisional biopsy was performed after MR-guided stereotactic needle localization. Histologic confirmation of a 6-mm ductal invasive breast cancer pT1bN0M0 was obtained for the incidental lesion visible in e–g, and confirmation of a myxoid fibroadenoma was obtained for the palpable lesion visible in b–d.

View larger version (182K): [in a new window]   Figure 5d. Breast MR images acquired in a 55-year-old patient with a palpable mass in the left upper outer quadrant. The mass had been rated as probably benign on the basis of mammographic and US findings. (a) Axial maximum intensity projection MR image from an early postcontrast subtracted data set of the diagnostic breast MR imaging study (220/4.5; flip angle, 80°). The maximum intensity projection image depicts two lesions (arrows): the expected palpable mass (P) and a nonpalpable, incidental lesion (I) in the left breast. (b) Early postcontrast and (c) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) show the palpable mass (P). (d) Time–signal intensity curve of the palpable mass shows a type I time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The palpable mass visible in b–d exhibits a suggestively strong early-phase enhancement, but it is well circumscribed, has a lobulated appearance, and reveals internal septations, which are all findings consistent with fibroadenoma. d further supports the diagnosis of a fibroadenoma. The signal intensity time course corresponds to a type Ib curve. (e) Early postcontrast and (f) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) obtained several sections cephalad of the palpable mass in b–d show the incidental lesion (arrow). (g) Time–signal intensity curve of the incidental lesion shows a type III time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The small, incidental, nonpalpable lesion visible in e–g shows the same rapid enhancement as the lesion visible in b–d. Also, it is well circumscribed and enhances homogeneously. However, it has a type III (washout) curve, which prompted the prospective diagnosis of an occult breast cancer, together with a fibroadenoma, in the same breast. Because the incidental lesion visible in e–g remained invisible at mammography (including spot compression) and at directed high-frequency breast US, excisional biopsy was performed after MR-guided stereotactic needle localization. Histologic confirmation of a 6-mm ductal invasive breast cancer pT1bN0M0 was obtained for the incidental lesion visible in e–g, and confirmation of a myxoid fibroadenoma was obtained for the palpable lesion visible in b–d.

View larger version (171K): [in a new window]   Figure 5e. Breast MR images acquired in a 55-year-old patient with a palpable mass in the left upper outer quadrant. The mass had been rated as probably benign on the basis of mammographic and US findings. (a) Axial maximum intensity projection MR image from an early postcontrast subtracted data set of the diagnostic breast MR imaging study (220/4.5; flip angle, 80°). The maximum intensity projection image depicts two lesions (arrows): the expected palpable mass (P) and a nonpalpable, incidental lesion (I) in the left breast. (b) Early postcontrast and (c) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) show the palpable mass (P). (d) Time–signal intensity curve of the palpable mass shows a type I time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The palpable mass visible in b–d exhibits a suggestively strong early-phase enhancement, but it is well circumscribed, has a lobulated appearance, and reveals internal septations, which are all findings consistent with fibroadenoma. d further supports the diagnosis of a fibroadenoma. The signal intensity time course corresponds to a type Ib curve. (e) Early postcontrast and (f) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) obtained several sections cephalad of the palpable mass in b–d show the incidental lesion (arrow). (g) Time–signal intensity curve of the incidental lesion shows a type III time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The small, incidental, nonpalpable lesion visible in e–g shows the same rapid enhancement as the lesion visible in b–d. Also, it is well circumscribed and enhances homogeneously. However, it has a type III (washout) curve, which prompted the prospective diagnosis of an occult breast cancer, together with a fibroadenoma, in the same breast. Because the incidental lesion visible in e–g remained invisible at mammography (including spot compression) and at directed high-frequency breast US, excisional biopsy was performed after MR-guided stereotactic needle localization. Histologic confirmation of a 6-mm ductal invasive breast cancer pT1bN0M0 was obtained for the incidental lesion visible in e–g, and confirmation of a myxoid fibroadenoma was obtained for the palpable lesion visible in b–d.

View larger version (167K): [in a new window]   Figure 5f. Breast MR images acquired in a 55-year-old patient with a palpable mass in the left upper outer quadrant. The mass had been rated as probably benign on the basis of mammographic and US findings. (a) Axial maximum intensity projection MR image from an early postcontrast subtracted data set of the diagnostic breast MR imaging study (220/4.5; flip angle, 80°). The maximum intensity projection image depicts two lesions (arrows): the expected palpable mass (P) and a nonpalpable, incidental lesion (I) in the left breast. (b) Early postcontrast and (c) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) show the palpable mass (P). (d) Time–signal intensity curve of the palpable mass shows a type I time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The palpable mass visible in b–d exhibits a suggestively strong early-phase enhancement, but it is well circumscribed, has a lobulated appearance, and reveals internal septations, which are all findings consistent with fibroadenoma. d further supports the diagnosis of a fibroadenoma. The signal intensity time course corresponds to a type Ib curve. (e) Early postcontrast and (f) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) obtained several sections cephalad of the palpable mass in b–d show the incidental lesion (arrow). (g) Time–signal intensity curve of the incidental lesion shows a type III time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The small, incidental, nonpalpable lesion visible in e–g shows the same rapid enhancement as the lesion visible in b–d. Also, it is well circumscribed and enhances homogeneously. However, it has a type III (washout) curve, which prompted the prospective diagnosis of an occult breast cancer, together with a fibroadenoma, in the same breast. Because the incidental lesion visible in e–g remained invisible at mammography (including spot compression) and at directed high-frequency breast US, excisional biopsy was performed after MR-guided stereotactic needle localization. Histologic confirmation of a 6-mm ductal invasive breast cancer pT1bN0M0 was obtained for the incidental lesion visible in e–g, and confirmation of a myxoid fibroadenoma was obtained for the palpable lesion visible in b–d.

View larger version (167K): [in a new window]   Figure 5g. Breast MR images acquired in a 55-year-old patient with a palpable mass in the left upper outer quadrant. The mass had been rated as probably benign on the basis of mammographic and US findings. (a) Axial maximum intensity projection MR image from an early postcontrast subtracted data set of the diagnostic breast MR imaging study (220/4.5; flip angle, 80°). The maximum intensity projection image depicts two lesions (arrows): the expected palpable mass (P) and a nonpalpable, incidental lesion (I) in the left breast. (b) Early postcontrast and (c) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) show the palpable mass (P). (d) Time–signal intensity curve of the palpable mass shows a type I time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The palpable mass visible in b–d exhibits a suggestively strong early-phase enhancement, but it is well circumscribed, has a lobulated appearance, and reveals internal septations, which are all findings consistent with fibroadenoma. d further supports the diagnosis of a fibroadenoma. The signal intensity time course corresponds to a type Ib curve. (e) Early postcontrast and (f) subtracted MR images from the dynamic series (220/4.5; flip angle, 80°) obtained several sections cephalad of the palpable mass in b–d show the incidental lesion (arrow). (g) Time–signal intensity curve of the incidental lesion shows a type III time course. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. The small, incidental, nonpalpable lesion visible in e–g shows the same rapid enhancement as the lesion visible in b–d. Also, it is well circumscribed and enhances homogeneously. However, it has a type III (washout) curve, which prompted the prospective diagnosis of an occult breast cancer, together with a fibroadenoma, in the same breast. Because the incidental lesion visible in e–g remained invisible at mammography (including spot compression) and at directed high-frequency breast US, excisional biopsy was performed after MR-guided stereotactic needle localization. Histologic confirmation of a 6-mm ductal invasive breast cancer pT1bN0M0 was obtained for the incidental lesion visible in e–g, and confirmation of a myxoid fibroadenoma was obtained for the palpable lesion visible in b–d.

View larger version (74K): [in a new window]   Figure 6a. MR images acquired in a 55-year-old patient who underwent breast MR imaging for routine follow-up after breast-conservation therapy and radiation therapy of her right breast 2 years previously. (a) Precontrast and (b) early postcontrast subtracted MR images (220/4.5; flip angle, 80°) from the dynamic breast study reveal a small lesion (arrow) with intermediate enhancement in the upper outer quadrant of the contralateral (left) breast. There is no enhancement in the scar tissue from the tumor removal on the right side. (c) Time–signal intensity curve of the lesion in the left breast shows that the early-phase enhancement rate is 75%. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. There is a washout of signal intensity in the intermediate postcontrast period, corresponding to a type III curve. Excisional biopsy findings confirmed the presence of a 6-mm invasive tubular breast cancer. There was no axillary lymph node involvement.

View larger version (89K): [in a new window]   Figure 6b. MR images acquired in a 55-year-old patient who underwent breast MR imaging for routine follow-up after breast-conservation therapy and radiation therapy of her right breast 2 years previously. (a) Precontrast and (b) early postcontrast subtracted MR images (220/4.5; flip angle, 80°) from the dynamic breast study reveal a small lesion (arrow) with intermediate enhancement in the upper outer quadrant of the contralateral (left) breast. There is no enhancement in the scar tissue from the tumor removal on the right side. (c) Time–signal intensity curve of the lesion in the left breast shows that the early-phase enhancement rate is 75%. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. There is a washout of signal intensity in the intermediate postcontrast period, corresponding to a type III curve. Excisional biopsy findings confirmed the presence of a 6-mm invasive tubular breast cancer. There was no axillary lymph node involvement.

View larger version (119K): [in a new window]   Figure 6c. MR images acquired in a 55-year-old patient who underwent breast MR imaging for routine follow-up after breast-conservation therapy and radiation therapy of her right breast 2 years previously. (a) Precontrast and (b) early postcontrast subtracted MR images (220/4.5; flip angle, 80°) from the dynamic breast study reveal a small lesion (arrow) with intermediate enhancement in the upper outer quadrant of the contralateral (left) breast. There is no enhancement in the scar tissue from the tumor removal on the right side. (c) Time–signal intensity curve of the lesion in the left breast shows that the early-phase enhancement rate is 75%. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. There is a washout of signal intensity in the intermediate postcontrast period, corresponding to a type III curve. Excisional biopsy findings confirmed the presence of a 6-mm invasive tubular breast cancer. There was no axillary lymph node involvement.

View larger version (60K): [in a new window]   Figure 7a. MR images acquired in a 27-year-old patient who underwent preoperative breast MR imaging for a palpable mass in the left breast. (a) First and (b) third postcontrast MR images (220/4.5; flip angle, 80°) from the dynamic series depict a strongly enhancing lesion (arrow) in the lower outer quadrant of the right breast. (c) First and (d) third postcontrast subtracted MR images (220/4.5; flip angle, 80°) correspond to a and b and show the same lesion (arrow). (e) The time–signal intensity curve of the lesion in the right breast shows a type III time course with washout. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. Owing to the strong washout phenomenon and the rapidly progressive signal intensity increase in the adjacent premenopausal parenchymal tissue, lesion delineation deteriorates rapidly in the postcontrast period. Lesion detectability is preserved only in the early postcontrast images. Excisional biopsy findings confirmed the presence of a 7-mm ductal invasive cancer in the right breast (pT1bN0M0G3). The palpable mass in the left breast did not enhance at breast MR imaging; excisional biopsy findings demonstrated nonproliferative dysplasia.

View larger version (68K): [in a new window]   Figure 7b. MR images acquired in a 27-year-old patient who underwent preoperative breast MR imaging for a palpable mass in the left breast. (a) First and (b) third postcontrast MR images (220/4.5; flip angle, 80°) from the dynamic series depict a strongly enhancing lesion (arrow) in the lower outer quadrant of the right breast. (c) First and (d) third postcontrast subtracted MR images (220/4.5; flip angle, 80°) correspond to a and b and show the same lesion (arrow). (e) The time–signal intensity curve of the lesion in the right breast shows a type III time course with washout. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. Owing to the strong washout phenomenon and the rapidly progressive signal intensity increase in the adjacent premenopausal parenchymal tissue, lesion delineation deteriorates rapidly in the postcontrast period. Lesion detectability is preserved only in the early postcontrast images. Excisional biopsy findings confirmed the presence of a 7-mm ductal invasive cancer in the right breast (pT1bN0M0G3). The palpable mass in the left breast did not enhance at breast MR imaging; excisional biopsy findings demonstrated nonproliferative dysplasia.

View larger version (61K): [in a new window]   Figure 7c. MR images acquired in a 27-year-old patient who underwent preoperative breast MR imaging for a palpable mass in the left breast. (a) First and (b) third postcontrast MR images (220/4.5; flip angle, 80°) from the dynamic series depict a strongly enhancing lesion (arrow) in the lower outer quadrant of the right breast. (c) First and (d) third postcontrast subtracted MR images (220/4.5; flip angle, 80°) correspond to a and b and show the same lesion (arrow). (e) The time–signal intensity curve of the lesion in the right breast shows a type III time course with washout. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. Owing to the strong washout phenomenon and the rapidly progressive signal intensity increase in the adjacent premenopausal parenchymal tissue, lesion delineation deteriorates rapidly in the postcontrast period. Lesion detectability is preserved only in the early postcontrast images. Excisional biopsy findings confirmed the presence of a 7-mm ductal invasive cancer in the right breast (pT1bN0M0G3). The palpable mass in the left breast did not enhance at breast MR imaging; excisional biopsy findings demonstrated nonproliferative dysplasia.

View larger version (66K): [in a new window]   Figure 7d. MR images acquired in a 27-year-old patient who underwent preoperative breast MR imaging for a palpable mass in the left breast. (a) First and (b) third postcontrast MR images (220/4.5; flip angle, 80°) from the dynamic series depict a strongly enhancing lesion (arrow) in the lower outer quadrant of the right breast. (c) First and (d) third postcontrast subtracted MR images (220/4.5; flip angle, 80°) correspond to a and b and show the same lesion (arrow). (e) The time–signal intensity curve of the lesion in the right breast shows a type III time course with washout. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. Owing to the strong washout phenomenon and the rapidly progressive signal intensity increase in the adjacent premenopausal parenchymal tissue, lesion delineation deteriorates rapidly in the postcontrast period. Lesion detectability is preserved only in the early postcontrast images. Excisional biopsy findings confirmed the presence of a 7-mm ductal invasive cancer in the right breast (pT1bN0M0G3). The palpable mass in the left breast did not enhance at breast MR imaging; excisional biopsy findings demonstrated nonproliferative dysplasia.

View larger version (114K): [in a new window]   Figure 7e. MR images acquired in a 27-year-old patient who underwent preoperative breast MR imaging for a palpable mass in the left breast. (a) First and (b) third postcontrast MR images (220/4.5; flip angle, 80°) from the dynamic series depict a strongly enhancing lesion (arrow) in the lower outer quadrant of the right breast. (c) First and (d) third postcontrast subtracted MR images (220/4.5; flip angle, 80°) correspond to a and b and show the same lesion (arrow). (e) The time–signal intensity curve of the lesion in the right breast shows a type III time course with washout. The x axis shows the dynamic imaging beginning time in seconds, and the y axis shows the intensity in arbitrary units. Owing to the strong washout phenomenon and the rapidly progressive signal intensity increase in the adjacent premenopausal parenchymal tissue, lesion delineation deteriorates rapidly in the postcontrast period. Lesion detectability is preserved only in the early postcontrast images. Excisional biopsy findings confirmed the presence of a 7-mm ductal invasive cancer in the right breast (pT1bN0M0G3). The palpable mass in the left breast did not enhance at breast MR imaging; excisional biopsy findings demonstrated nonproliferative dysplasia.