Synopsis

Differentiation of intra-cranial-mass-lesions (ICMLs), particularly infective vs neoplastic is difficult using conventional MRI. In the current study, the potential of amide proton transfer weighted (APT-w) contrast for differentiating infective and neo-plastic-mass-lesions has been investigated. APT-w contrast was computed and optimized with respect to different types of normalizations and region-of-interests (ROIs) selection. There was substantial overlap of APT-w contrast values among ICMLs. Different normalizations showed significant difference (P<0.05) in differentiating various groups among ICMLs. Histogram analysis played an important role in significant differentiation (P<0.05) of ICMLs. Thus, APT-MRI can enhance diagnostic accuracy.

INTRODUCTION

METHODS

All the MRI experiments were performed at 3T whole body Ingenia MRI system (Philips) using a 15-channel d-stream head-neck coil for reception using a pulse-sequence reported previously¹⁰. Thirty-two patients of varying etiologies with neo-plastic mass lesions [Low Grade (LG) tumor(n=14), High Grade (HG) tumor(n=8), lymphoma (n=3)] and infective mass lesions [Tuberculoma(TBM) (n=6), tubercular-abscess (n=1)] were scanned in the current study. APT-w images were acquired at following frequency offsets: ±2.5, ± 3, ± 3.5, ±4, ±4.5 ppm from water and corrected for B₀ inhomogeneity using B₀ maps generated by WASSR¹¹ approach (range is -1.5 to +1.5 ppm; interval is 0.125 ppm).

DATA PROCESSING: We used four types of normalizations for computing APT-w contrast:

Type-1: APT-w contrast normalized with M₀

_{$$APT_{M_0} = \frac{M_{sat(-3.5ppm)} - M_{sat(+3.5ppm)}}{M_{0}}\times100$$}

where, M_sat(+3.5ppm) and M_sat(-3.5ppm) are the signal intensities with upfield and downfield of water resonating frequency. M₀ is the signal intensity without radio-frequency saturation.

Type-2: APT-w contrast normalized with M_sat(-3.5ppm)

_{$$APT_{Neg} = \frac{M_{sat(-3.5ppm)} - M_{sat(+3.5ppm)}}{M_{sat(-3.5ppm)}}\times100$$}

Type-3: APT-w contrast normalized with M₀ and NAWM

_{$$APT_{M_{0}-NAWM} = {APT_{M_0} - M_{NAWM}}$$}

where, M_NAWM is the mean value of APT_M0 in normal-appearing-white-matter(NAWM)

Type-4: APT-w contrast normalized with M_sat(-3.5ppm) and NAWM

_{$$APT_{Neg-NAWM} = {APT_{Neg} - M_{NAWM}}$$}

Here, M_NAWM is calculated from APT_Neg

Different types of ROIs were drawn on lesions of APT-w maps. ROI-1 was drawn on entire lesion region. cROI-2 was placed on contra-lateral region of ROI-1. ROI-2 was placed on inner-most portion of lesion (or necrotic region where lesion has necrosis). cROI-2 was placed contra-lateral to ROI-2. ROI-3 was the region on periphery of lesions with APT-w contrast more than 75^th percentiles of periphery area (or ring region for lesions with necrotic tissue). cROI-3 was placed contra-lateral to ROI-3. Histogram analysis¹² of APT_{M0_NAWM} and APT_{Neg_NAWM} corresponding to ROI-1 were carried out. Following histogram parameters were calculated : (a) mean, (b) standard deviation (SD), (c) median, (d) mode, (e) kurtosis, (f) skewness, (g) entropy, (h) full-width-at-half-maximum (FWHM), (h) mean of the values greater than 10^th, 25^th, 50^th, 75^th, 90^th percentile (mtop10, mtop25, mtop50, mtop75, mtop90) of APT-w contrast. Student T-test with two tails, ANOVA with Tukey post-hoc test, receiver-operation-characteristics (ROC) - sensitivity, specificity, accuracy, cut off and area under curve (AUC) were computed to differentiate ICMLs. P<0.05 was considered significant.

RESULTS

DISCUSSION

CONCLUSION

Acknowledgements

References

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