Comparison of Signal intensity measures with absolute T1 value quantification in patients undergoing serial follow up imaging in patients with neurocysticercosis
Pradeep Kumar Gupta1, Prativa Sahoo2, Alok Kumar Singh3, Ravindra Kumar Garg3, Rupsa Bhattacharjee4, and Rakesh Kumar Gupta1

1Radiology and Imaging, Fortis Memorial Research Institute, Gurgaon, India, 2Healthcare, Philips India ltd, Bangalore, India, 3Department of Neurology, KG Medical University, Lucknow, India, 4Healthcare, Philips India ltd, Gurgaon, India

Synopsis

Gadolinium based contrast agents are necessary for MRI for disease detection and therapy. Studies reported gadolinium remains in brain for long time after injecting contrast particularly in follow up patients undergoing serial contrast applications. T1 signal intensity increases slowly due to contrast accumulation in brain. Our study quantifies T1 relaxation time as a measure for follow up contrast patients. Results show absolute T1 significantly decreases in Gray Matter regions, putamen, thalamus and globus pallidus. We conclude that absolute T1 quantification can efficiently pick up deposition of gadolinium much earlier than T1 signal intensity changes as observed in Gray matter regions.

Purpose

Use of Gadolinium based contrast agents (CA) are essential adjuncts to MR imaging in a wide spectrum of diseases for detection of the disease and therapeutic guidance. Most of the routine MRI imaging protocols includes gadolinium based post-contrast imaging 1. It has been reported that gadolinium may remain in brain after contrast MRI for a long time. Some recently published studies showed increased signal intensities (SI) on unenhanced T1-weighted MR images after serial application of gadolinium-based contrast agent 2,3. The increased signal intensity due to contrast accumulation in pre contrast images could generate bias for clinicians in examining diseases which shows T1 hyper intense. Furthermore it may also affect post-acquisition quantitative processing. Our study was designed to see after how many time of administration CA the contrast accumulation starts to visible in the imaging and examine how the signal intensity performs viz a viz absolute quantification of T1 value in the regions which shows deposition of gadolinium on histology as per the literature.

Method

Our study includes 23 patients (male=11, female=12, mean age=21.47±7.72 years) with calcified cysticercosis single lesion who had undergone gadolinium-based contrast agents MR imaging five time. To compare changes in SI and absolute T1 value between first and fifth time scan we have selected different gray matter (GM) and white matter (WM) regions. GM regions include putamen, thalamus, globus pallidus (GP) and caudate nucleus (CN). WM regions include frontal white matter (FWM), occipital white matter (OWM), temporal white matter (TWM), genu and splenium of the corpus callosum. Images of each time point were registered with the first time point using SPM8. Mean and SD of SI and T1 at GM and WM regions were estimated and used for statistical analysis by placing ROIs of 20-40mm2 on T1-weighted axial image and on absolute T1 map respectively. Repeated measure and paired t-test was performed to observe SI changes and only paired t-test between first and fifth time point was performed to observe T1 changes. All the statistical analysis was performed using SPSS (version 16.0, SPSS Inc, Chicago, USA) statistical software. P values ≤ 0.05 were considered to be significant. The study was approved by the Institutional Ethics Committee. All the imaging was done on a 3T MRI scanner. All the patients was assessed during year 2012–2015 and followed up every six month. The MR imaging protocol includes pre contrast 3D T1-weighted (TR/TE=8.4/3.3 ms, number of slice = 136, slice thickness = 1 mm, FOV = 240 mm, image matrix = 512 × 512, TI = 400 ms, and flip angle = 13°), inversion recovery images ( TR=940 ms, TE=8 ms, TI = 800 and 1600 ms, number of slice = 12, section thickness = 6 mm, FOV = 240×240 mm2 and matrix = 128 × 128). Voxel wise pre-contrast tissue longitudinal relaxation time (T10) was quantified using Inversion recovery images 4. Each visit of the patient a dose of 0.1mmol/kg body weight Gd-DTPA was administered intravenously through a power injector at 5 mL/s rate.

Results

Table 1 shows the paired t-test results between the first time point value with those obtained on fifth time point. Result shows T1 significantly decrease in GM regions, putamen (1st time point= 1245.43±146.09; 5th time point= 1159.67±148.90), thalamus (1st time point= 1279.8±154.7; 5th time point= 1148.3±212.9) and GP (1st time point= 1203.5±147.04; 5th time point= 1109.2±161.09); however caudate nuclei and different WM regions showed no significant changes. Signal intensity shows no significant change in selected GM and WM regions on paired t test as well as on repeated measurement test.

Discussion and Conclusion

We observed no significant change in the signal intensity on pre contrast images in various grey and white matter region in this study. However the quantitative value showed significant reduction in T1 values in some of the grey matter regions. It suggests that quantitative T1 measure may pick up the deposition of gadolinium earlier that quantitative signal intensity changes as were observed in this study in some of the grey matter regions. However the clinical implications of this observation are still not clear. Use of T1 quantification in the first and the fifth study is the limitation of this study.

Acknowledgements

No acknowledgement found.

References

1. Radbruch A et al. Radiology. 2015;275:783-91.

2. McDonald RJ et al. Radiology. 2015;275:772-82

3. Kanal E et al. Radiology. 2015;275:630-4.

4. Sahoo P et al. J Magn Reson Imaging. 2013;38:677-88.

Figures

Table 1: Result of paired t-test between First and fifth time point



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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