Brain MR Imaging and ¹H-MR Spectroscopy Changes in Patients with Extrahepatic Portal Vein Obstruction from Early Childhood to Adulthood

Neuropsychological Tests

Each subject completed a neuropsychological test battery especially designed for children, adolescents, and adults, which was adopted for an Indian population to identify abnormalities in neuropsychological functions. The Revised Amsterdamse Kinder Intelligentie Test containing a battery of 9 subsets was used for children.¹⁶ However, trail-making tests and a performance subset of the modified Wechsler Adult Intelligence Scale was used for adolescents and adults. The patients were considered to have MHE if they had 2 or more abnormal neuropsychological tests,^11,17 while the rest of the patients with less than 2 abnormal neuropsychological tests were considered to have no MHE.

Diagnosis of EHPVO

Diagnosis of EHPVO was based on consensus guidelines of the Asian Pacific Association for the Study of Liver.¹ EHPVO patients included in this study either presented with splenomegaly or variceal bleeding or both. We could not find any evidence of procoagulant disorders or any specific disease predisposing to portal vein thrombosis in these patients and they were presumed to be “idiopathic”. The presumed duration of illness in the pediatric age group was 5.5 ± 3.4 years, in adolescents it was 6.2 ± 4.6 years, and in adult patients it was 8.15 ± 5.4 years. This quantification of duration was based on the first clinical symptoms reported by the patients such as variceal bleeding or splenomegaly or both. EHPVO patients with a history of overt hepatic encephalopathy in the past, recent upper gastrointestinal bleeding, antibiotic intake in the last 6 weeks, evidence of chronic liver disease on investigation, or any neurologic/psychiatric disorders were excluded from the study. The study protocol was approved by our institutional ethics committee, and written informed consent was obtained from each subject or from caregivers. All patients were evaluated with blood tests (hemogram, liver function tests, and prothrombin time), imaging (abdominal sonography, Doppler for portal vein), and upper gastrointestinal endoscopy for assessment of varices. Spleen size was determined by clinical examination. The spleen was considered to be enlarged when it was palpable below the costal margin, and its maximal length from the 11th rib was measured by using a tape. In controls the spleen was not palpable and its length was considered to be 0. Blood ammonia was determined before MR imaging and after overnight fasting by using a standard enzymatic ultraviolet method.

MR Imaging and ¹H-MR Spectroscopy

MR imaging was performed on a 1.5T MR imaging scanner (Signa LX, 9.1; GE Healthcare Technologies, Milwaukee, Wisconsin) by using a standard quadrature birdcage transmit-and-receive radio frequency head coil. T1-weighted, T2-weighted, and diffusion tensor images were performed in all patients and age/sex-matched controls. T1-weighted images were used for placement of spectroscopy voxel; however, T2-weighted imaging was used to look for any structural abnormality. T1-weighted fast spin-echo imaging with TR of 1000 ms, TE of 14 ms, NEX of 2, and T2-weighted fast spin-echo imaging using TR of 6000 ms, TE of 85 ms, and NEX of 4 were taken. DTI was acquired by using a single-shot echo-planar dual SE sequence with ramp sampling.¹⁸ A balanced rotationally invariant¹⁹ diffusion encoding scheme with 10 uniformly distributed directions over the unit sphere was used for obtaining the diffusion-weighted data. The b factor was set to 0 and 1000 s/mm², TR of 8 s, and TE of 100 ms. A total of 36 axial sections were acquired with image matrix of 256 × 256 (following zero-filling) section thickness of 3 mm with no intersection gap and a FOV of 240 × 240 mm² in T1-weighted, T2-weighted, and diffusion tensor images. To enhance the signal intensity–to-noise ratio and reduce the phase fluctuations, magnitude-constructed images were repeated (NEX of 8) and temporally averaged.

Spectra were obtained with and without water suppression. Localized single voxel point-resolved spectroscopy included TR/TE of 3000 ms/35 ms and number of averages of 64. A voxel of 2 × 2 × 2 cm³ was located mainly in the right basal ganglion region of the brain in all cases. It has been reported that changes in basal ganglia are most characteristic of hepatic encephalopathy in cirrhosis with MHE^20,21; hence, this specific location was selected for spectroscopy voxel placement. The voxel localization was guided by the T1-weighted axial images as shown in Fig 1A. After global shimming, voxel shimming was performed, and a full width at half maximum of 4–6 Hz was achieved in all cases. The total time required for MR imaging and ¹H-MR spectroscopy was 17 minutes 30 seconds.

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Fig 1.

A, Shows spectroscopy voxel placed on right basal ganglia region in healthy adult control on T1-weighted image. B, Axial gray scale fractional anisotropy map fused with mean diffusivity map shows regions of interest placement at the level of third ventricle from where FA and MD values have been obtained. In addition, large spectroscopy voxel co-registered with this map shown in this figure to quantify FA and MD values for the purpose of correlation of these indices (Fig 2). C–F, LC Model processed localized ¹H-MR spectroscopy from the right basal ganglia region show metabolite pattern of choline, Glx, myo-inositol, and NAA in adult control (C), EHPVO child (D), EHPVO adolescent (E), and EHPVO adult (F). The EHPVO child and adolescent spectra show increased Glx while EHPVO adult shows increased Glx and decreased myo-inositol compared to control. Values of choline, creatine, and NAA in all age groups of patients is comparable to controls (Table 4).

Data Analysis and Quantification

The DTI data were processed as described in detail elsewhere.²² Briefly, after image cropping and distortion corrections, the data were interpolated to attain isotropic voxels and decoded to obtain the tensor field for each voxel. The tensor field data were then diagonalized by using the analytic diagonalization method²² to obtain the eigenvalues (λ₁, λ₂, and λ₃) and the 3 orthonormal eigenvectors. The tensor field data and eigenvalues were used to compute the DTI metrics such as MD and FA for each voxel.

Regions of interest were placed at the level of third ventricle on bilateral internal capsules (posterior and anterior limb), bilateral caudate nuclei, putamen, thalami, globus pallidus, cingulate gyrus, frontal and occipital white matter, genu, and splenium in patients and healthy controls to quantify MD and FA (Fig 1 B). We selected these regions of interest, as these structures have been shown to be abnormal in previous studies^11,12 and they may be affected in hepatic encephalopathy. The size of the regions of interest varied from 3.5 to 32 mm², with shape varying from elliptical to rectangular. Additionally, coordinates of spectroscopy were co-registered with MD maps in each subject, and MD and FA values from this large voxel (right basal ganglion region) were also measured to correlate these with spectroscopy-derived metabolites and blood ammonia (Fig 1B).

For processing and quantification of all individual ¹H-MR spectroscopy data (Fig 1 C–F), the LCModel software package (LCModel 6.2; Stephen Provencher, Oakville, Ontario, Canada) was used.²³ The metabolite concentrations of NAA, choline, creatine, Glx, and myo-inositol were calculated. After processing with the LCModel, spectral data with line width at full width at half maximum of >6 Hz and signal intensity–to-noise ratio of >3 were included in the study. All spectra were assessed for general quality by experienced observers.

Statistical Analysis

Left and right measurements of DTI metrics of all regions except for genu and splenium were pooled together, and averaged values of different regions were used for the final dataset for statistical analysis. ANOVA post hoc Bonferroni multiple comparisons were performed to detect the difference in EHPVO with and without MHE as compared with controls in the biochemical parameters, blood ammonia, DTI metrics, and metabolites. To study the relationship between ¹H-MR spectroscopy coordinate-derived MD with blood ammonia and metabolites, the Pearson correlation coefficient was computed. For computation of Pearson correlation, the values of different parameters in all 3 age groups were pooled together. A value of P < .05 was chosen to establish significance between the groups. All statistical data computations were performed by using SPSS (version 16.0, SPSS, Chicago, Illinois).