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DWI Learning Module

DWI Learning Module. ACRIN 6698: Diffusion Weighted MR Imaging Biomarkers for Assessment of Breast Cancer Response to Neoadjuvant Treatment: A sub-study of the I-SPY 2 TRIAL. DWI Quality.

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DWI Learning Module

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  1. DWI Learning Module ACRIN 6698: Diffusion Weighted MR Imaging Biomarkers for Assessment of Breast Cancer Response to Neoadjuvant Treatment: A sub-study of the I-SPY 2 TRIAL

  2. DWI Quality • In this training guide, non fat-suppressed and fat-suppressed T1+Gd MRI are also provided with low b-value (b=0 s/mm2) and high b-value (b=800 s/mm2) DWI to illustrate how fat, non-fat parenchyma, fluids and dense lesions may look on low and high b-value DWI. • Factors to be considered for evaluating DWI quality are illustrated.

  3. 10/10/2012 T.Chenevert, S.Partridge SHIM Quality • DWI requires good fat suppression and most fat suppression techniques (ChemSat, FatSat; SPIR; SPAIR) require good shim quality over the imaged breast volume. Use your most reliable shim and fat-suppression techniques when performing DWI.

  4. 10/10/2012 T.Chenevert, S.Partridge Fat Suppression • The technologist needs to have reasonable sense of the patient’s breast composition (amount of fatty vs. non-fat breast parenchyma) prior to performing the DWI in order to better evaluate the quality of the DWI. • In ACRIN 6698, high resolution non fat-suppressed and fat-suppressed T1+Gd images ARE NOT acquired prior to diffusion scans. However, the “survey” images or, when available, prior MRI exams should be adequate to indicate the amount of fatty vs non-fatty content in a given patient.

  5. 10/10/2012 T.Chenevert, S.Partridge Very Fatty Breasts • Breasts composed of nearly all fatty tissue with very little non-fat parenchyma will likely yield visually low SNR diffusion weighted images. Properly-performed fat suppression, which is essential for high-quality DWI, should eliminate nearly all the available signal (see examples 2&3). The small amount of non-fat tissue and blood/fluids should remain as signal on the low b-value DWI (b=0). • On the high b-value DWI (b=800), signal from these non-fat tissues also becomes suppressed, although truly dense tissue and many solid lesions will retain much of their signal. Thus, dense lesions tend to be more conspicuous on high b-value DWI. Even though fat suppression is essential, it is imperfect. Fat signal that is not fully suppressed may appear to gain relative signal strength at high b-value DWI since the non-fat tissues are losing signal as diffusion weighting increases whereas residual fat signal is unaffected by diffusion weighting.

  6. NonFatSat T1 Example 1 DWI b=0 FatSat T1+Gd DWI b=800 Good DWI Quality: Uniform FatSat & dense tissue/tumor is relatively bright on high bvalue DWI

  7. NonFatSat T1 Example 2 DWI b=0 FatSat T1+Gd DWI b=800 DWI of fatty breast: Good fat suppression will eliminate nearly all signal. DWI at b=0 shows non-fat signal (eg, blood vessels and parenchyma), but DWI at high b further suppresses this non-fat signal. This can give the appearance of poor fat suppression on high b DWI.

  8. Example 3 DWI b=0 Not Available DWI b=800 Not Available DWI of fatty breast: Expect low SNR since good fat suppression should eliminate nearly all signal. DWI at b=0 shows remaining non-fat signal (eg, blood vessels and little parenchyma), but DWI at high b further suppresses this non-fat signal. Signal from dense tissue/lesions should remain.

  9. NonFatSat T1 Example 4 DWI b=0 FatSat T1+Gd DWI b=800 Acceptable DWI Quality: Uniform FatSat. On high b DWI, expect lower SNR and an “apparent increase” in fat signal due to DWI suppression of water signal.

  10. NonFatSat T1 Example 5 DWI b=0 FatSat T1 DWI b=800 Poor Shim = Poor FatSat = Poor Quality DWI: Unsuppressed fat signal due to poor shim is shifted by many pixels along the phase-encoding/fold-over direction and may obscure lesions. Breast distortion also increases with poor shim. Use your most reliable shim & fat-suppression techniques.

  11. NonFatSat T1 Example 6 DWI b=0 FatSat T1+Gd DWI b=800 Good DWI Quality: Uniform FatSat, low distortion. Dense tissue/lesion may appear relatively brighter on high b DWI.

  12. Example 7 DWI b=0 Not Available FatSat T1 DWI b=800 Good FatSat but low/moderate DWI SNR: if possible, increase averages but keep DWI scantimeto ~5mins.

  13. Appendix • Additional DWI case examples

  14. Example 8 DWI b=0 Not Available DWI b=800 Not Available Low to Moderate DWI SNR: if possible, increase averages but keep DWI scantimeto ~5mins

  15. NonFatSat T1 Example 9 DWI b=0 DWI b=800 Not Available Acceptable DWI Quality

  16. Example 10 DWI b=0 Not Available DWI b=800 Not Available Low DWI Quality: Non uniform FatSat may be obscuring lesion/parenchyma

  17. Example 11 DWI b=0 Not Available DWI b=800 Not Available Moderate Quality DWI: Unsuppressed fat and/or parallel imaging artifact obscures lesion of interest.

  18. NonFatSat T1 Example 12 DWI b=0 FatSat T1+Gd DWI b=800 Acceptable Quality DWI: Bright fluid on b=0 DWI is suppressed on high b DWI. Fat signal may appear relatively brighter on high b DWI. DWI often exhibit spatial distortion.

  19. NonFatSat T1 Example 13 DWI b=0 FatSat T1+Gd DWI b=800 Acceptable Quality DWI

  20. NonFatSat T1 Example 14 DWI b=0 FatSat T1+Gd DWI b=800 Acceptable to Good DWI Quality

  21. NonFatSat T1 Example 15 DWI b=0 FatSat T1+Gd DWI b=800 Acceptable to Good DWI Quality

  22. NonFatSat T1 Example 16 DWI b=0 FatSat T1+Gd DWI b=800 Good Quality DWI

  23. NonFatSat T1 Example 17 DWI b=0 FatSat T1+Gd DWI b=800 Good Quality DWI

  24. Example 18 DWI b=0 Not Available DWI b=800 Not Available Acceptable Quality DWI

  25. NonFatSat T1 Example 19 DWI b=0 FatSat T1+Gd DWI b=800 Acceptable DWI Quality

  26. NonFatSat T1 Example 20 DWI b=0 FatSat T1+Gd DWI b=800 Acceptable DWI Quality

  27. Diffusion Weighted Image (DWI) Quality In this training guide, non fat-suppressed and fat-suppressed T1+Gd MRI are also provided with low b-value (b=0 s/mm2) and high b-value (b=800 s/mm2) DWI to illustrate how fat, non-fat parenchyma, fluids and dense lesions may look on low and high b-value DWI. 1) FAT: The technologist needs to have reasonable sense of the patient’s breast composition (amount of fatty vs. non-fat breast parenchyma) prior to performing the DWI in order to better evaluate the quality of the DWI. In ACRIN 6698, high resolution non fat-suppressed and fat-suppressed T1+Gd images ARE NOT acquired prior to diffusion scans. However, the “survey” images or, when available, prior MRI exams should be adequate to indicate the amount of fatty vs non-fatty content in a given patient. 2) VERY FATTY BREASTS: Breasts composed of nearly all fatty tissue with very little non-fat parenchyma will likely yield visually low SNR diffusion weighted images. Properly-performed fat suppression, which is essential for high-quality DWI, should eliminate nearly all the available signal (see examples 2&3). The small amount of non-fat tissue and blood/fluids should remain as signal on the low b-value DWI (b=0). On the high b-value DWI (b=800), signal from these non-fat tissues also becomes suppressed, although truly dense tissue and many solid lesions will retain much of their signal. Thus, dense lesions tend to be more conspicuous on high b-value DWI. Even though fat suppression is essential, it is imperfect. Fat signal that is not fully suppressed may appear to gain relative signal strength at high b-value DWI since the non-fat tissues are losing signal as diffusion weighting increases whereas residual fat signal is unaffected by diffusion weighting. 3) SHIM QUALITY: DWI requires good fat suppression and most fat suppression techniques (ChemSat, FatSat; SPIR; SPAIR) require good shim quality over the imaged breast volume. Use your most reliable shim and fat-suppression techniques when performing DWI. Breast_DWI_TrainingSetTLChenevert Apr, 2012

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