Spectroscopy Of The Breast



Spectroscopy Of The Breast


Peter Stanwell, PhD

Carolyn Mountford, D.Phil



Terminology


Abbreviations



  • Magnetic resonance spectroscopy (MRS)


Definitions



  • Detectable biochemicals are distinguished by their resonance frequency, line shape, line width, phase, and peak area


Anatomy-Based Imaging Issues


Overview



  • MRS success depends on



    • Appropriate pre-acquisition set up


    • Acquisition protocol


    • Post-processing


    • Shimming for MRS acquisition is essential to overcome magnetic field inhomogeneities


  • MRS pitfalls



    • B0 inhomogeneities are often dominant factor limiting successful MRS


    • Some breast coils are not optimized for spectroscopy


    • Presence of biopsy clips may affect shimming


    • Some gadolinium-based MR agents have been shown to affect breast MRS


    • Lipids



      • Localized shimming more difficult due to abundance of adipose tissue with different susceptibility from surrounding glandular (and malignant) tissue


      • Impact of unwanted lipid signals can be reduced by decreasing amplitude of lipid signal


      • Techniques for lipid suppression exist for use in MRS


Spectroscopy Acquisition Protocols


Data Acquisition



  • Parameters set during pre-scan include power calibrations, frequency adjustment, shimming, and water suppression adjustment



    • Shimming = process by which B0 field is made as homogeneous as possible, typically using linear x-, y-, and z-gradient coils


    • Water suppression = process by which water signal is suppressed to allow detection of important metabolites


Spectroscopy Processing


Processing Steps



  • Water referencing



    • Aligns spectral resonances against water set at 4.74 ppm


    • Allows for correction of resonance distortions using water signal as reference


  • Apodization



    • In clinical application, this mathematical function is used to improve SNR


  • Zero filling



    • Method of improving spectral resolution


  • Fourier transformation



    • Converts time domain signal into frequency domain


  • Phase correction



    • Allows for correction of distortions in final spectrum


  • Baseline correction



    • Allows for correction of baseline errors in final spectrum


    • Vertical display may need to be increased to see resonances between 3.00 and 3.40 ppm


Spectra Interpretation


Malignant vs. Benign



  • Key metabolite in breast spectroscopy is choline resonance at 3.23 ppm


  • Malignant breast cancers show resonance at 3.23 ppm


  • Benign breast lesions show resonance at 3.28 ppm



    • This resonance is reported in breast tissue in lactating and other healthy women


Differential Diagnosis


Invasive Tumor



  • Early single series showed sensitivity of 100% and specificity of 88%


Ductal Carcinoma in Situ



  • Early stage DCIS (no microinvasion) has spectral characteristics of benign lesion (in vitro studies)


  • DCIS with microinvasion has same spectral profile as malignant tumor



    • These results need to be verified with larger studies

Sep 18, 2016 | Posted by in OBSTETRICS & GYNAECOLOGY IMAGING | Comments Off on Spectroscopy Of The Breast
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