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1 Department of Radiology, St. Marianna University School of Medicine, 2-16-1
Sugao, Miyamae-ku, Kawasaki City, Kanagawa 216-8511, Japan.
2 Department of Surgery, St. Marianna University School of Medicine, Miyamae-ku,
Kawasaki City, Kanagawa 216-8511, Japan.
3 Philips Medical Systems Corporation, Philips Bldg., 2-13-37 Kohnan, Minato-ku,
Tokyo 108-8507, Japan.
Received May 13, 2003;
accepted after revision October 23, 2003.
Address correspondence to Y. Kanemaki
(yoshihid{at}tc4.so-net.ne.jp).
Introduction
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Nine of 15 patients underwent surgery, and the following histopathologic diagnoses were established: ductal carcinoma in situ (n = 2), intraductal papilloma (n = 3), invasive ductal carcinoma (n = 2), papillomatosis (n = 1), and mammary duct ectasia (n = 1). Mammography, sonography, and MR mammary ductography were performed in all patients. In 10 of 15 patients, MR mammary ductography was followed by conventional ductography for comparison. The interval between MR ductography and conventional ductography was between 0 and 10 days.
MRI was performed using a 1.5-T Intera Master unit (Philips Medical Systems). All patients underwent imaging in the prone position. A microscopy coil with a diameter of 4.7 cm was used as a surface coil to acquire signal data from the ductal system (Fig. 1). Construction of this coil allowed local acquisition of the signal with a high signal-to-noise ratio. This high signal-to-noise ratio was used to increase spatial resolution by acquiring a 512 x 256 matrix for a 7-cm field of view, resulting in a 0.137-mm in-plane resolution, much higher than that of existing coils (0.7–3.0 mm) (Fig. 2A, 2B). An inherent property of these small coils, which display high local sensitivity, is that signal yield at greater distances from the coil is low. This problem was overcome using a postprocessing technique that provided a correction, resulting in a uniform signal level. The technique was performed by acquiring auxiliary signals from the small coil itself and also from a body coil. These supplementary signals were used to produce auxiliary values, which were then used to correct image data from the small coil. This technique was accomplished using CLEAR (constant level appearance) software (Philips Medical Systems).
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Axial T2-weighted (TR/TE, 1,500/120) turbo spin-echo and axial T1-weighted (43/8.7; flip angle, 50°) 3D fast-field echo images were obtained using a fat-saturation technique and the CLEAR algorithm with a slice thickness of 1.6 mm (0.8-mm overlap) and a 512 x 256 matrix. Scanning time for both T1- and T2-weighted images was approximately 5 min.
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Conventional ductography was performed in 10 of 15 patients. Intraductal tumors were visualized on conventional ductography in seven of 10 patients, and MR mammary ductography detected all tumors shown on conventional ductography (Fig. 3A, 3B).
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In one patient, MR mammary ductography detected an intraductal tumor that was not visualized on conventional ductography. In two cases, neither MR mammary ductography nor conventional ductography detected a tumor. One of these cases was subsequently surgically proven to be mammary duct ectasia with no tumor apparent (Fig. 4A, 4B), and surgery was not performed in the other case.
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MRI is a noninvasive procedure providing high contrast resolution that has recently been proposed to assess intraductal lesions. However, MRI with conventional coils cannot detect small intraductal lesions of more than a few millimeters. To overcome this limitation, we used a microscopy coil to allow the acquisition of images at spatial resolutions as high as 100 µm. On the basis of our initial study, MR mammary ductography using a microscopy coil can show ducts measuring 0.8 mm in diameter and intraductal tumors as small as 1.0 mm. This ultrahigh spatial resolution suggests that MR mammary ductography may offer a feasible alternative to conventional ductography. MR mammary ductography showed all intraductal elevated lesions that were visualized on ductography and also detected additional lesions that were not seen on conventional ductography. One patient with negative results after MR mammary ductography was surgically proven to have mammary duct ectasia with no apparent tumor. Our initial results with MR mammary ductography suggest excellent detectability of small intraductal lesions.
The mammary ducts are usually shown as hyperintense structures on T1-weighted images and are isointense to mammary glands on T2-weighted images. This unique signal intensity pattern is probably attributable to protein-rich or hemorrhagic fluid in mammary ducts [6, 7]. Both T1- and T2-weighted images are therefore necessary for complete visualization of mammary ducts. Orel et al. [6] described high-signal-intensity fluid-filled ducts on T1-weighted images in two of six patients. We are unsure of the reasons for the different incidences of hyperintense fluid on T1-weighted images between their series and our study. Possible explanations include differences in concentrations of hemorrhage and protein in the fluid and divergent sequence parameters.
MR mammary ductography offers a number of advantages. The technique shows all mammary ducts fully in the field of view, whereas conventional ductography can visualize only the duct into which contrast material is injected. This benefit of MR mammary ductography allows the detection of additional intraductal lesions, including those in different ducts, in one image set. Also, if the mammary duct is completely occluded, conventional ductography cannot show tumors peripheral to the occlusion. MR mammary ductography can visualize both peripheral and proximal ducts, resulting in a higher probability of detecting additional intraductal lesions.
Our series encountered a higher percentage of malignant lesions than reported in other investigations. Further studies with the inclusion of more benign papillomas are needed for precise evaluation of MR ductography. Possible limitations of MR mammary ductography are similar to those of conventional MRI, including the inability to scan patients with implanted pacemakers and image degradation caused by motion.
In conclusion, MR mammary ductography is a useful, reliable, safe, and less invasive procedure for assessing intraductal lesions and offers a potential alternative to conventional ductography.
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