Participants Characteristics
Among the 53 eligible patients, five were excluded due to lack of WHO 4-tier classification (n=1), poor imaging quality (n=3), or corrupt data following post-processing (n=1) (Fig.1). Forty-eight patients with untreated glioma were ultimately enrolled, including 25 in low-grade glioma (WHO grade II; mean age of 38 ±11 years, 10 females/15 males) and 23 in high-grade glioma (WHO grade III and IV; mean age of 53 ±10 years, 13 females/10 males). All the tumor tissue were obtained by surgical operation, and IDH gene mutation status were identified in 47 gliomas. Patient demographic, histopathology, molecular and image characteristics are shown in Table 1. Among these 48 patients with VSASL-CBV images, 32 patients had evaluable DSC-PWI imaging, and 44 had evaluable VSASL-CBF for comparison.
Table1. Baseline patient characteristics and perfusion measures for low-grade and high-grade gliomas.
Parameters
|
Low-Grade Glioma (n=25)
|
High-Grade Glioma (n=23)
|
P Value
|
Clinical data
|
|
|
|
Sex
|
|
|
.25
|
No. of women
|
10 (40)
|
13 (57)
|
|
No. of men
|
15 (60)
|
10 (43)
|
|
Mean age ±(y)
|
38±11
|
53±10
|
<.001
|
WHO grade
|
II
|
25
|
-
|
-
|
III
|
-
|
9
|
-
|
IV
|
-
|
14
|
-
|
Quantitative parameters at baseline perfusion MRI
|
VSASL rTBF a
|
1.32 (1.01– 1.63)
|
2.58 (1.81 – 3.17)
|
<.001
|
|
VSASL rTBV a,b
|
2.93 (2.20– 3.98)
|
6.49 (5.14– 7.78)
|
<.001
|
|
DSC-PWI rTBV a,c
|
3.41 (1.82– 3.95)
|
6.28 (5.10– 7.23)
|
<.001
|
|
Note. Unless otherwise indicated, data are numbers and data in parentheses are percentages.
DSC-PWI = dynamic susceptibility contrast-enhanced perfusion-weighted imaging, VSASL = velocity-selective arterial spin labeling, rTBF = relative tumor blood flow, rTBV = relative tumor blood volume.
a Data are median and interquartile range.
b With 44 patients analyzed.
c With 32 patients analyzed.
Visual Assessment
The two independent readers evaluated the conspicuity of the glioma with an overall weighted kappa of 0.80 (95% CI: 0.70 - 0.90), indicating good agreement. Averaged scores (2.26 ± 0.76) of visual assessments of the two readers showed good conspicuity of glioma on VSASL based CBV maps with all patients, and slightly better conspicuity on high-grade glioma with averaged scores of 2.30 ± 0.66 compared to low-grade (2.24 ± 0.84). Representative images of astrocytoma and glioblastoma are shown in two cases (Fig.2a, b). CBV and CBF maps derived from VSASL and DSC-PWI are largely comparable on visual inspection. As expected, low-grade astrocytoma did not show elevated CBV (Fig.2a), in contrast to glioblastoma with markedly elevated CBV (Fig.2b). Representative cases of different visual scores between low-grade and high-grade glioma are shown on Supplement Fig.1.
Correlation and Agreement between VSASL and DSC-PWI derived rTBV
The inter-observer agreement for quantitative parameters was excellent, with ICCs between 0.934 and 0.987 (Table 2). A high correlation was observed between rTBV values of VSASL and DSC-PWI in 32 patients (R2 = 0.83, P<0.001, Fig.3a). Bland-Altman plots further confirmed the agreement in rTBV between the two techniques (Fig.3b).
Table 2. Raw data and inter-reader agreement of measurements of all the measured quantitative parameters between two readers.
|
Reader 1
|
Reader 2
|
ICCs (95% CI)
|
VSASL rTBF
|
1.93±0.98
|
1.91±0.90
|
0.987 (0.976 - 0.993)
|
VSASL rTBV
|
4.64±1.91
|
4.68±1.89
|
0.934 (0.883 - 0.963)
|
DSC-PWI rTBV
|
4.54±2.14
|
4.72±2.12
|
0.971 (0.940 - 0.986)
|
DSC-PWI = dynamic susceptibility contrast-enhanced perfusion-weighted imaging,
VSASL = velocity-selective arterial spin labeling,
rTBF = relative tumor blood flow, rTBV = relative tumor blood volume,
CI = confidence interval, ICC = intraclass correlation coefficients,
Glioma Grading
Both VSASL and DSC-PWI derived rTBV, as well as VSASL derived rTBF showed clear distinction between low-grade and high-grade gliomas (Fig.4). The median rTBF and rTBV values in low-grade glioma were all significantly lower than those of high-grade for VSASL-rTBF (1.32 vs. 2.58), VSASL-rTBV (2.93 vs. 6.49), and DSC-PWI-rTBV (3.41 vs. 6.28), P<0.001 (Table 1). The ROC curves showed that VSASL-derived rTBV yielded excellent diagnostic performance in glioma grading with rTBV showing slightly higher accuracy than VSASL-derived rTBF (AUC: 0.94 vs. 0.89) (Fig.5), and comparable with DSC-PWI derived rTBV (AUC: 0.94 vs. 0.93). The optimal threshold and diagnostic performance of each technique are listed in Table 3. Compared to rTBF derived from VSASL, rTBV derived from VSASL showed consistently higher diagnostic sensitivity (87.0% vs. 73.7%), positive (95.2% vs. 93.3%) or negative (88.9% vs. 82.8%) predictive values, and accuracy (91.7% vs. 86.4%) for glioma grading (Table 3). The diagnostic performance of rTBV derived between VSASL and DSC-PWI was comparable (Fig.5, Table 3).
Table 3. Diagnostic performances of VSASL derived rTBF, rTBV, and DSC-PWI derived rTBV in preoperatively grading of gliomas.
Quantitative parameters at baseline perfusion MRI
|
AUC a
|
Threshold
|
Sensitivity (%)b
|
Specificity (%)b
|
PPV (%)b
|
NPV (%)b
|
Accuracy (%)b
|
P value
|
VSASL rTBF
|
0.89 (0.79 – 0.99)
|
>1.97
|
73.7 (14/19)
|
96.0 (24/25)
|
93.3 (14/15)
|
82.8 (24/29)
|
86.4 (38/44)
|
<.001
|
VSASL rTBV
|
0.94 (0.88 – 1.00)
|
>4.84
|
87.0 (20/23)
|
96.0 (24/25)
|
95.2 (20/21)
|
88.9 (24/27)
|
91.7 (44/48)
|
<.001
|
DSC-PWI rTBV
|
0.93 (0.84 – 1.00)
|
>4.38
|
87.5 (14/16)
|
93.8 (15/16)
|
93.3 (14/15)
|
88.2 (15/17)
|
90.6 (29/32)
|
<.001
|
DSC-PWI = dynamic susceptibility contrast-enhanced perfusion-weighted imaging,
VSASL = velocity-selective arterial spin labeling,
rTBF = relative tumor blood flow, rTBV = relative tumor blood volume,
AUC = area under the receiver operating characteristic curve, PPV = positive predictive value, NPV = negative predictive value,
a Numbers in parentheses are 95% confidence intervals.
b Numbers in parentheses are raw data.