Synthesizing a Contrast-Enhancement Map in Patients with High-Grade Gliomas Based on a Postcontrast MR Imaging Quantification Only

Abstract

Background and purpose: Administration of a gadolinium-based contrast agent is an important diagnostic biomarker for blood-brain barrier damage. In clinical use, detection is based on subjective comparison of native and postgadolinium-based contrast agent T1-weighted images. Quantitative MR imaging studies have suggested a relation between the longitudinal relaxation rate and proton-density in the brain parenchyma, which is disturbed by gadolinium-based contrast agents. This discrepancy can be used to synthesize a contrast-enhancement map based solely on the postgadolinium-based contrast agent acquisition. The aim of this study was to compare synthetic enhancement maps with subtraction maps of native and postgadolinium-based contrast agent images.

Materials and methods: For 14 patients with high-grade gliomas, quantitative MR imaging was performed before and after gadolinium-based contrast agent administration. The quantification sequence was multidynamic and multiecho, with a scan time of 6 minutes. The 2 image stacks were coregistered using in-plane transformation. The longitudinal relaxation maps were subtracted and correlated with the synthetic longitudinal relaxation enhancement maps on the basis of the postgadolinium-based contrast agent images only. ROIs were drawn for tumor delineation.

Results: Linear regression of the subtraction and synthetic longitudinal relaxation enhancement maps showed a slope of 1.02 ± 0.19 and an intercept of 0.05 ± 0.12. The Pearson correlation coefficient was 0.861 ± 0.059, and the coefficient of variation was 0.18 ± 0.04. On average, a volume of 1.71 ± 1.28 mL of low-intensity enhancement was detected in the synthetic enhancement maps outside the borders of the drawn ROI.

Conclusions: The study shows that there was a good correlation between subtraction longitudinal relaxation enhancement maps and synthetic longitudinal relaxation enhancement maps in patients with high-grade gliomas. The method may improve the sensitivity and objectivity for the detection of gadolinium-based contrast agent enhancement.

Fig 1.

A, Measured proton-density values as a function of R₁ relaxation rate values of a slice of a brain of a patient with glioma grade IV before administration of GBCA (at 3T). The solid line traverses the average position of gray matter and white matter, indicating the predetermined, linear relationship between R₁ and PD for the native brain parenchyma. The dotted line indicates a threshold of 0.2 seconds⁻¹ from the solid line. B, PD and R₁ of the same slice after GBCA administration in which the present glioma exhibits enhancement. Some R₁ values are substantially increased above the dotted threshold line. The estimated R₁ enhancement corresponds to the measured R₁ value minus the corresponding R₁ value on the predetermined solid line.

Fig 2.

Images of the same slice as in Fig 1: synthetic T1-weighted imaging using native data (A), synthetic T1-weighted imaging using post-GBCA data (B), the native R₁ map (C), the post-GBCA R₁ map (D), the difference map of the coregistered native map (E), and the post-GBCA R₁ synthetic-difference map based on the post-GBCA acquisition only (F).

Fig 3.

2D histogram of the R₁ enhancement found using the subtraction of native and post-GBCA R₁ maps as a function of the synthetic R₁ enhancement, based on the post-GBCA acquisition only, of all included patients. The black and white intensity in the plot is proportional to the number of times an x, y coordinate occurred. The diagonal line indicates equivalence.

Fig 4.

Zoomed part around the tumor displayed in Fig 2. Synthetic T1-weighted imaging using native data (A), synthetic T1-weighted imaging using post-GBCA data (B), the ROI line as drawn by a neuroradiologist to encapsulate the border of the enhancing tumor (C). D, Synthetic R₁ enhancement map shown as a green overlay on the synthetic T1-weighted image in which full color corresponds to dR₁ = 1.0 seconds⁻¹. The minimum enhancement was set at dR₁ = 0.2 seconds⁻¹. Some low-intensity enhancement is visible outside the yellow ROI. The red line indicates the edge of the intracranial volume.

Fig 5.

Other examples of the synthetic R₁ enhancement map and low-intensity enhancement at the edges of high-intensity enhancement in gliomas. Left: native synthetic T1-weighted image. Center: post-GBCA synthetic T1-weighted image. Right: synthetic R₁ enhancement map as a green overlay. The color indicates a range of dR₁ of 0.2–1.0 seconds⁻¹. The red line indicates the edge of the intracranial volume.