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Chemical Shift MRI Is There any Contribution to Morphologic Evaluation of Solid Breast Masses?

Posted Sep 30, 2009 Updated Apr 7, 2023
By Gokhan Gokalp MD , Ugur Topal MD , Naile Bolca MD , Ilker Ercan PhD
9 min read

Rationale and Objectives

To investigate the contribution of chemical shift magnetic resonance imaging for assessment of the margins of solid breast masses by benefiting from India ink artifact.

Methods and Materials

Eighty-eight masses in 64 patients were evaluated in T1- and T2-weighted images, dynamic contrast and chemical shift studies according to Breast Imaging Reporting and Data System magnetic resonance lexicon. Subtraction images were automatically obtained by chemical shift imaging and dynamic studies. Each sequence was scored using a scale of 1 to 5 according to its ability to demonstrate margins separate from surrounding parenchyma. Breast parenchyma was evaluated as fatty and dense. The results were compared with the histopathologic results.

Results

Twenty-eight (31.8%) of the lesions were localized in fatty breast, and the remaining 60 (68.2%) lesions were localized in dense breast. There were 34 (38.6%) benign and 54 (61.4%) malignant masses. In fatty breast, chemical shift subtraction and T1-weighted images were valuable both for the demonstration and differentiation of benign lesions ( P < .05). None of the sequence was valuable for both the demonstration and differentiation of malignant lesions in fatty breasts ( P > .05). In dense breasts, chemical shift subtraction and dynamic contrast subtraction images were valuable for both the demonstration and differentiation of benign and malignant lesions. Additional to these sequences, T2-weighted images was also valuable for benign lesions ( P < .05).

Conclusion

Chemical shift subtraction can contribute to routine dynamic contrast subtraction in morphologic analysis particularly for the evaluation of margins of benign lesions in fatty breasts. It can also help in morphologic analysis of masses in dense breast.

Magnetic resonance imaging (MRI) has become an important modality in the breast imaging practice. MRI has a higher sensitivity of detection of breast cancer than mammography and ultrasonography (US) . But approximately, 8%–10% of invasive breast cancers cannot be detected. Along with the technical factors, varying degrees of contrast enhancement of different lesions and excessive enhancement of glandular tissue may be the causes of missed cancers . Both morphologic and enhancement characteristics are used for the evaluation of the lesions . Subtraction method is used for better evaluation of morphology and enhancement characteristics of the lesions.

Chemical-shift MRI is based on the fact that hydrogen atoms of water and fat molecules have different precession frequencies . Chemical shift subtraction (CSS) technique is obtained by subtracting in-phase images from out-phase images. CSS, which gives information about the fat content of the lesion and surrounding structures, has been successfully used in the differentiation of fat-containing adenomas of adrenal gland . Chemical shift imaging includes two types of margin artifacts: chemical shift artifact and India ink artifact. Chemical shift artifact, also known as misregistration artifact, occurs as a result of misregistration of signal across the frequency-encoding direction because of signals failing to part from desired spatial frequency encoding due to different resonance frequencies in water and fat. India ink artifact is seen due to water and fat protons existing in the same voxel. In voxels localized in close proximity to water-fat interfaces, water and fat protons exist at similar ratios, and because those spins exhibit a 180° opposed direction in out-phase, signal loss occurs (phase cancellation). In out-phase image, interface areas appear black as if drawn by India ink because of signal loss. This is known as India ink artifact, or fat water artifact or black lining artifact . Because of the India ink artifact, the margin of a mass containing no fat appears as black at the mass-surrounding fat interface on out-phase image ( Fig. 1 ). On the subtraction image obtained from subtraction of out-phase image from in-phase image, mass is seen as black and margin is seen bright making it more obvious from surrounding structures ( Fig. 1 ).

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Figure 1

Chemical shift imaging. (a) In-phase. (b) Out-phase images. India ink artifact is seen as a black line on the interface areas of fat-water. (c) Subtraction image. Interface areas of fat-water are seen as a well-defined bright line. Breast is fatty.

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Materials and methods

Patients

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MRI Technique

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Analysis of the Images

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Histopathologic Correlation

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Statistical Analysis

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Results

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Table 1

Histopathology of Lesions ( n = 88)

Benign ( n = 34) Fibroadenoma 21 Fibrocystic changes 5 Intraductal papilloma 2 Focal fibrosis 2 Fat necrosis 2 Reactive lymphoid hyperplasia 1 Mastitis 1 Malignant ( n = 54) Invasive ductal carcinoma 45 Invasive lobular carcinoma 4 Invasive carcinoma with ductal and lobular features 2 Medullar carcinoma 1 Papillary carcinoma 1 Tubular carcinoma 1 Total ( n = 88)

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Table 2

Distribution of Final Radiologic Diagnosis of Lesions ( n = 88) on each Sequence

Fatty and Dense Breast T1-weighted T2-weighted DCS CSS Benign Malignant Inadequate Benign Malignant Inadequate Benign Malignant Inadequate Benign Malignant Inadequate Benign 15 2 17 19 3 12 12 6 16 22 3 9 Malignant 2 21 31 3 19 32 3 46 5 5 35 14P value <.001 <.001 .496 <.001 .005 .028 <.001 <.001 <.001 <.001 <.001 .963 Fatty Breast T1-weighted T2-weighted DCS CSS Benign Malignant Inadequate Benign Malignant Inadequate Benign Malignant Inadequate Benign Malignant Inadequate Benign 5 2 1 4 2 2 0 3 5 5 3 0 Malignant 2 14 4 3 12 5 1 16 3 2 14 4P value .009 .044 1.00 .142 .209 1.00 1.00 .068 .022 .009 .199 .294 Dense Breast T1-weighted T2-weighted DCS CSS Benign Malignant Inadequate Benign Malignant Inadequate Benign Malignant Inadequate Benign Malignant Inadequate Benign 10 0 16 15 1 10 12 3 11 17 0 9 Malignant 0 7 27 0 7 27 2 30 2 3 21 10P value <.001 .015 .127 <.001 .121 .001 <.001 <.001 <.001 <.001 <.001 .667

DCS: dynamic contrast subtraction; CSS: chemical shift subtraction.

Graphic 1, Mean values assigned to margins in fatty and dense breasts according to sequences (scores: 1–5).

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Figure 2, A 45-year-old woman with a mass detected in mammography screening. Breast tissue is fatty, and the mass measuring 7 × 5 mm with circumscribed, smooth margins is seen in the left breast. (a) Mass is seen on T1-weighted image but margin is not seen well enough to make benign-malignant distinction ( moderate ). (b) Margins can be distinguished on T2-weighted image ( good ). (c) Lesion is not seen on dynamic contrast subtraction image ( indistinct ). (d) On chemical shift subtraction (CSS) image, India ink artifact surrounding the lesion helps to distinguish margins easily ( very good ). Bright regions on CSS image reflect fat-mass/glandular tissue interface areas. Histopathology: fibroadenoma.

Figure 3, A 44-year-old woman presented with palpable mass. Breast is dense, and a mass measuring 22 × 22 mm with irregular margins was detected in the left breast. (a,b) Lesion margin is fairly distinct on T1- and T2-weighted images ( good ). (c,d) Lesion margin is distinct on dynamic contrast subtraction (DCS) and chemical shift subtraction (CSS) images ( very good ). Note that spiculations on the medial margin are more obvious on CSS image compared with that of the DCS image because of India ink artifact. Histopathology: invasive ductal carcinoma.

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Figure 4, A 51-year-old woman with a mass detected on mammography. Breast is dense, and a mass in the left breast, measuring 16 × 12 mm with circumscribed smooth margin is seen. (a) Margin is well-defined on T1-weighted image ( very good ). Margin is indeterminate ( indistinct ) on T2-weighted images (b) and partially indeterminate ( poor ) on dynamic contrast subtraction (DCS) image at early and late phases because of insufficient enhancement. (c) Margin is well-defined and smooth on chemical shift subtraction (CSS) image because of India ink artifact surrounding the lesion ( very good ). (d) Histopathology: fibroadenoma.

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Figure 5, A 40-year-old woman presented with a palpable mass. Breast is dense, and a mass measuring 23 × 13 mm with spiculated margin is detected in the right breast. (a) Margin is indeterminate ( indistinct ) on T1-weighted and T2-weighted images. (b) Margin is spiculated on DCS image ( very good ). (c) Margin and spiculations are well defined on chemical shift subtraction (CSS) image ( very good ). Histopathology: invasive ductal carcinoma.

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Discussion

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Academic Radiology, Volume 16, Issue 10
Journals General Radiology
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