MODULE 3. Further laboratory and imaging examinations related to breast cancer diagnostics
3.5. Technological principles and the variety of techniques – how does breast MRI work
In the MRI machines used for breast MRI, the strength of the magnetic field is between 1.5-3 Tesla.
The routine sequences are:
In some special cases the following sequences are used:
The routine sequences are:
- T2-weighted imaging (with and without fat saturation)
- T1-weighted imaging with fat saturation but also with and without contrast media
In some special cases the following sequences are used:
- Diffusion weighted imaging
- MR spectroscopy (Hukkinen 2013)
Photos © PPSHP (Pohjois-Pohjanmaan sairaanhoitopiiri, Northern Ostrobothnia Hospital District).
T2-weighted imaging
T2-weighted imaging gives good information about the structure of breast tissue and helps differentiate between malignant and benign lesions. Benign lesions usually contain more water and for this reason they show up bright in T2-weighted images (See image 1). However, radiologists should be familiar with the characteristics of all possible lesions, because there are several rare types of malignant lesions that can also appear bright in T2-weighted images (Westbrook & Talbot 2011).
Dynamic contrast-enhanced MR-imaging (DCE-MRI)
DCE-MRI of the breast has a good ability to detect breast lesions. It is more accurate than mammography or ultrasound for determining the extent of the disease when the diagnosis is recent.
DCE-MRI is used in addition to or instead of mammography
Silicone implants can also be examined by using DCE-MRI (Youssef et al. 2016)
.
DCE-MRI is used in addition to or instead of mammography
- for women at high risk
- for women with extremely dense breasts
- when mammography doesn’t give the opportunity to provide a clear diagnosis
- in case of highly invasive breast cancers
Silicone implants can also be examined by using DCE-MRI (Youssef et al. 2016)
.
Photos © PPSHP (Pohjois-Pohjanmaan sairaanhoitopiiri, Northern Ostrobothnia Hospital District).
Fat saturated imaging
All of the key sequences used in breast MRI can benefit from the use of fat saturation, and some even require it. It is important to use fat saturation when scanning breasts, because breasts consist mostly of fat tissue. Fat gives out a high signal which appears bright in images because of its log T2 relaxation time. This can cause a low signal lesion to be unnoticed, which can naturally lead to misdiagnosis. Using fat saturation in T1- and T2-weighted sequences can enhance contrast and improve the visibility when examining the morphology of the breast tissue (Lin & Rogers & Maijidi 2015).
Most sequences are also used without fat saturation to depict anatomical detail and to identify fat tissue, but for instance DCE-MRI and T2-weighted sequences should always be done with fat saturation as well.
T2-weighted sequence with fat saturation can be useful when an ’indirect’ ductography image without contrast media is needed.
Most sequences are also used without fat saturation to depict anatomical detail and to identify fat tissue, but for instance DCE-MRI and T2-weighted sequences should always be done with fat saturation as well.
T2-weighted sequence with fat saturation can be useful when an ’indirect’ ductography image without contrast media is needed.
- Conventional ductography is perfomed using a mammography machine and injecting contrast media (gadolinium) into the lactiferous ducts.
- T2-weighted fat saturated image can help detect small cancers without the contrast media (Lin & Rogers & Maijidi 2015).
Gradient echo
Gradient echo is faster than conventional spin echo. Breast MRI is very susceptible to movement artefacts caused by breathing during the imaging process. Artefacts can be reduced using gradient echo sequences (Westbrook & Talbot 2011).
Diffusion weighted imaging (DWI) and MR spectroscopy (MRS)
DWI and MRS are not a part of the standard breast imaging protocol, but they can be used in differential diagnostics in special cases
MRS can help to determine the metabolic profile of a breast lesion, such as choline levels, to differentiate between benign and malignant tumours.
Both DWI and MRS are helpful as a part of assessing the response to neoadjuvant chemotherapy in early stages. |
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References
- Hukkinen K. Rintojen magneettikuvaus. Lääketieteellinen aikakauskirja Duodecim, 2013; 20. (http://www.duodecimlehti.fi/lehti/2013/20/duo11278)
- Lin C, Rogers CD, Majidi S. Fat suppression techniques in breast magnetic resonance imaging: a critical comparison and state of the art. Reports in Medical Imaging. 2015; (8): 37–49. (http://www.dovepress.com/fat-suppression-techniques-in-breast-magnetic-resonance-imaging-a-crit-peer-reviewed-article-RMI)
- Youssef MA, Elahwal HMS, Alwageeh MM, Attya SE. Role of MRI in differentiating bening from malignant breast lesions using dynamic contrast enhanced MRI and diffusion weighted MRI. Alexabdria Journal of Medicine. 2016.(http://ac.els-cdn.com/S2090506816300562/1-s2.0-S2090506816300562-main.pdf?_tid=103f4818-50da-11e7-8ecc-00000aacb362&acdnat=1497428496_704eba15adfe6b05b01d9b79f64a3e1f)
- Westbrook C, Talbot J. MRI in practice, 2011.