Kinetic Curves



Kinetic Curves


Julie A. Ritner, MD










Sagittal T1 C+ FS MR (left) and axial angiomap image (right) show a rapidly enhancing oval mass with spiculated margins image. Mixed kinetics image are seen. Pathology was grade II IDC.






Kinetics of the mass in the previous images show medium (50-100% at 90 sec) initial enhancement image with persistent (blue) image, plateau (yellow) image, and washout (red) image delayed-phase curves.


TERMINOLOGY


Abbreviations and Definitions



  • Kinetics: Dynamic contrast enhancement characteristics of lesion



    • Initial and delayed phases


    • Objective evaluation = plotted graph of ROI enhancement time-course points



      • Visual analysis is subjective; limited by progressive glandular enhancement


  • Enhancement



    • Post-contrast T1 signal intensity of lesion compared with pre-contrast signal


  • Dynamic acquisition



    • Sequential T1W FS imaging before and after contrast administration


    • Refers to temporal resolution



      • 1st post-contrast acquisition should be < 2 minutes after injection to capture peak initial enhancement


      • Peak enhancement may occur later


      • Ideally 60-90 seconds per acquisition


  • Region of interest (ROI)



    • Selected area within enhancing lesion for analysis of time-course kinetics



      • Selective ROI (3-4 pixels) important for accurate evaluation


      • Larger ROIs lead to averaging of kinetic features and falsely less suspicious appearance


      • Can be drawn manually and plotted over time


      • ROI summaries can be generated by computer-aided detection (CAD) software


      • Most suspicious enhancement should be reported


  • Time-signal intensity curve (TIC) = kinetic curve



    • Graph of ROI pixel value over time


    • Initial phase: Enhancement pattern within 1st 2 minutes or when curve starts to change (per BI-RADS)


    • Delayed phase: Enhancement pattern after 1st 2 minutes or when curve starts to change (per BI-RADS)


  • Maximum intensity projection (MIP)



    • 3D reconstruction of 1st post-contrast subtraction series


  • Subtraction series



    • Post-processed images created by subtracting pre-contrast series from selected post-contrast series



      • Clearly displays areas of enhancement


    • Used in 2D imaging as “fat-suppressed” images


    • Patient motion may lead to image misregistration and false depiction of enhancement


    • MIP images generated from 1st post-contrast subtraction series


  • Signal intensity (SI)


  • Dynamic contrast-enhanced (DCE) MR = modified post-contrast acquisition



    • Very high temporal resolution at expense of spatial resolution


    • To assess physiologic parameters (vessel permeability, tissue perfusion, & others)



      • Research evaluating neoadjuvant chemotherapy response


ENHANCEMENT ANALYSIS


Initial Phase



  • Early enhancement, determined by signal change from baseline pre-contrast series to 1st post-contrast series


  • Most optimal phase for cancer detection: Greatest T1 difference between enhancing cancer and background


  • Predictive kinetic feature


  • Qualitative and quantitative assessment described



    • Qualitative: Visual assessment of enhancement intensity


    • Quantitative: Calculated assessment, used for kinetic curve analysis



      • Defined as percent signal increase from pre-contrast signal to 1st post-contrast series


      • Slow, medium, rapid


  • Threshold of initial phase determines presence or absence of CAD color assignment



    • Below threshold: Slow enhancement (< 50% SI increase) does not receive color assignment




      • Typically benign, though morphology must determine level of suspicion


      • Time-course not predictive for level of suspicion


    • Lower threshold: Medium (> 50% SI increase) and rapid receive color assignment


    • Higher threshold: Only rapid (≥ 100% SI increase) receives color assignment



      • Invasive cancers typically show rapid enhancement


      • Benign parenchyma, benign proliferative and inflammatory lesions, and benign lymph nodes may show rapid enhancement


    • Can be manually adjusted to different levels of sensitivity


Delayed (Post-Initial) Phase



  • Kinetic time point analysis after initial phase



    • Variable number of delayed time points depending on temporal resolution, typically 4-6


    • Peak enhancement may occur in initial phase or later in delayed phase


    • Minimum of 1 point required (4-7 minutes post-injection) to define curve shape


  • Curve type determined by time point analysis after peak enhancement



    • Type I curve = persistent: > 10% continued increase in signal intensity after peak enhancement



      • Typically benign pattern, though suspicious morphology should prompt biopsy


      • Multiple foci of persistent enhancement may be benign pattern (may be described as moderate or marked background enhancement)


    • Type II curve = plateau: Steady signal intensity after peak enhancement



      • ± 10% of peak signal intensity


      • Suspicious pattern: 64-77% PPV for malignancy


    • Type III curve = washout: > 10% decrease in signal intensity after peak enhancement



      • Highly suspicious pattern: 87-92% PPV


      • Washout may occur in later delayed phase (at 3-4 minutes), considered suspicious


      • Benign lesions may show washout, lowering specificity: Lymph nodes, adenosis, papillomas


  • Identification of curve shapes has high interobserver agreement (κ = 0.85)


Post-Processing






    • Software programs that automate image post-processing, in particular regarding enhancement kinetics



      • Kinetics demonstrated by color-coded parametric overlays in areas of threshold enhancement


    • Post-processing is subject to potential errors



      • Rigorous quality control is essential to avoid misdiagnoses and false-negative interpretations


      • Cardiac kinetic curve (rapid enhancement with washout) verifies contrast administration and correct processing


      • Knowledge of software limitations, artifacts, and potential pitfalls is important


  • Threshold enhancement



    • Presence of CAD color assignment based on initial enhancement reaching selected threshold


  • Generates color parametric overlay of enhancement kinetics, subtraction and MIP images, and ROI summaries



    • Parametric kinetic mapping shows color overlay of areas that reach threshold enhancement



      • Specific color assignment based on delayed-phase enhancement curves (type I, II, or III); color assignments vary with each vendor


      • False washout color assignment can be seen with misregistration from patient motion


      • Absence of color assignment of rapidly enhancing masses can occur with incorrect image processing


    • MIPs useful for background enhancement, vascularity, and focal enhancing lesions



      • Increased breast vascularity associated with invasive cancers


    • ROI summaries



      • Enhancement curves are generated on pixel by pixel basis


  • MR interpretation should not be based solely on CAD-generated images




    • CAD images are post-processed and may show false analyses if processed incorrectly


    • Source images must always be reviewed


MR FEATURES & INTERPRETATION


Overview



  • High MR sensitivity for cancer detection largely due to rapid enhancement of invasive carcinomas



    • Reported sensitivity, specificity, and accuracy of TIC

      analysis: 91-96%; 83-86%; 86%


    • Enhancement occurs in benign lesions and normal fibroglandular tissue


    • Kinetic analysis improves specificity


  • High temporal resolution essential for accurate kinetic analysis


Anatomic Considerations



  • Enhancement related in part to vessel density and capillary permeability



    • Benign fibroglandular tissue is hormonally responsive and may show suspicious enhancement


    • Tumor neovascularity causes rapid enhancement and washout


Mass



  • Most predictive feature: Margin morphology > enhancement kinetics


  • Presence of any type of enhancement is important



    • Typical invasive cancers show rapid enhancement with plateau or washout kinetics


    • Up to 15% of invasive malignancies may show slow enhancement


    • 94-100% NPV for nonenhancement to exclude invasive cancer


NMLE



  • Morphology > > kinetics



    • Slow enhancement with delayed peak could lead to false-negative interpretation


    • 20% of invasive cancers in high-risk patients were NMLE (1 series)


  • 70-96% sensitivity for MR DCIS detection



    • 10-16% of DCIS lesions show no enhancement


  • Symmetry useful to determine level of suspicion


Kinetic Analysis Pitfalls



  • 1st post-contrast scan > 2 minutes



    • Misses peak enhancement, falsely benign curve


  • False-negative study



    • Absent contrast



      • Suspect with strongly “negative” MIP


      • Validate contrast injection: Cardiac kinetic curve


    • Cancer not included in field of view


    • Excessive compression, limits enhancement


    • Incorrect post-processing


  • Misregistration due to patient motion



    • Suspect with nonphysiologic jagged curve shape


    • May mimic suspicious enhancement


    • Edge artifact = color artifact at fat-parenchyma interfaces



REFERENCES

1. Kuhl C: The current status of breast MR imaging. Part I. Choice of technique, image interpretation, diagnostic accuracy, and transfer to clinical practice. Radiology. 244(2):356-78, 2007

2. Lehman CD et al: A new automated software system to evaluate breast MR examinations: improved specificity without decreased sensitivity. AJR Am J Roentgenol. 187(1):51-6, 2006

3. Schnall MD et al: Diagnostic architectural and dynamic features at breast MR imaging: multicenter study. Radiology. 238(1):42-53, 2006

4. Kuhl CK et al: Dynamic bilateral contrast-enhanced MR imaging of the breast: trade-off between spatial and temporal resolution. Radiology. 236(3):789-800, 2005

5. Szabó BK et al: Dynamic MR imaging of the breast. Analysis of kinetic and morphologic diagnostic criteria. Acta Radiol. 44(4):379-86, 2003






Image Gallery









Kinetic curve analysis includes initial phase, defined as percent signal change from pre-contrast, at 90 secs to 2 mins. Rapid & medium enhancement typically get color assignments. Slow enhancement does not receive color.






Delayed-phase enhancement determines curve type. Type 1 = persistent (blue); type 2 = plateau (yellow); type 3 = washout (red). Color assignments vary by CAD vendors.






(Left) Staging MR in a 41 year old with a palpable mass, malignant on FNA, shows the malignancy as a heterogeneously enhancing round mass with spiculated margins on dynamic sagittal (left) and delayed axial (right) image images. (Right) Sagittal T1WI C+ FS MR (left) and axial delayed image (right) of the same breast show a 2nd mass, oval, smooth, with nonenhancing septations, and rapid initial and plateau delayed enhancement image.






(Left) Sagittal T1WI C+ FS MR with color shows the known malignancy to have rapid initial enhancement (color assignment) with dominantly persistent (type I: Blue) and plateau (type II: Yellow) delayed kinetics. (Right) Sagittal T1WI C+ FS MR with CAD color overlay shows the 2nd mass to have rapid initial enhancement and only persistent (blue) delayed kinetics. Morphology and kinetics suggest a probably benign mass. Biopsy proved a fibroadenoma.






(Left) Kinetic curve from the same known malignancy shows rapid initial-phase enhancement (> 100% at 90 seconds) image with persistent (type I: Blue) image and plateau (type II: Yellow) image delayed-phase curves. (Right) Kinetic curve from the fibroadenoma shows rapid initial enhancement (> 100% at 90 seconds) image and persistent (type I) image delayed enhancement.

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Sep 18, 2016 | Posted by in OBSTETRICS & GYNAECOLOGY IMAGING | Comments Off on Kinetic Curves
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