Diffusion-Weighted Imaging of Upper Abdominal Organs Acquired with Multiple B-Value Combinations: Value of Normalization Using Spleen as the Reference Organ

Characterization of the evaluation method for hepatobiliary phase image by liver magnetic resonance imaging using Gd-EOB-DTPA

PURPOSE

This study aimed to characterize quantitative liver-spleen contrast (Q-LSC) and hepatocellular uptake index (HUI) for evaluating hepatobiliary phase (HBP) images using gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) in liver magnetic resonance imaging and to identify differences in the results obtain from these two measurement methods.

METHODS

Twenty-nine consecutive randomly selected patients were assessed using the 3.0 T MR system. Three regions of interest (ROI) were set for the liver parenchyma and spleen, and signal intensity (SI) was averaged. Q-LSC (SI of the liver divided by the SI of the spleen) and HUI [(Q-LSC-1) × liver volume] were calculated. Moreover, the volume and mean SI of the whole liver and spleen, left lateral segment (LLS), and the other segments were calculated. Subsequently, ROI-based and volume-based values for Q-LSC (R-LSC and V-LSC) and HUI (R-HUI and V-HUI), and the whole and each segment were compared.

RESULTS

R-LSC and V-LSC for the whole and each segment were not significantly different. Conversely, all combinations of HUI, except between R-HUI and V-HUI were significantly different (P < 0.01), for the whole liver. Correlations between R-LSC, R-HUI, and volume-based LLS were lower than the others.

CONCLUSION

Q-LSC and HUI were characterized through an imaging evaluation of HBP with Gd-EOB-DTPA. R-LSC and R-HUI, or V-HUI, of the whole liver were strongly correlated, but the LLS affected the data, and HUI depends on liver volume. R-LSC is simple and easy to use for HBP evaluation.

Influences of the second motion probing gradient b-value and T2 relaxation time on magnetic resonance diffusion-derived 'vessel density' (DDVD) calculation: the examples of liver, spleen, and liver simple cyst

Background

Magnetic resonance (MR) diffusion-derived 'vessel density' (DDVD) is calculated according to: DDVDb0b2 = Sb0/ROIarea0 - Sb2/ROIarea2, where Sb0 and Sb2 refer to the tissue signal when b-value is 0 or 2 s/mm2. Sb2 and ROIarea2 can also be approximated by other low b-values diffusion-weighted imaging (DWI). This study investigates the influence of the second motion probing gradient b-value and T2 on DDVD calculations of the liver, spleen, and liver simple cyst. Literature analysis shows the liver and spleen have very similar amounts of perfusion. At 3T, liver and spleen have a T2 of around 42 and 60 ms respectively, while cyst has a very long T2.

Methods

Twenty-eight subjects had 1.5T DWI data with b-values of 0, 1, 2, 15, 20, 30 s/mm2. Twenty-one subjects had 3.0T DWI data with b-values of 0, 2, 4, 7, 10, 15, 20, 30 s/mm2. DDVDb0b1, DDVDb0b2, DDVDb0b4, DDVDb0b7, DDVDb0b10, DDVDb0b15, DDVDb0b20, and DDVDb0b30 were calculated from b=0 and b=1 images, b=0 and b=2 images, b=0 and b=4 images, b=0 and b=7 images, b=0 and b=10 images, b=0 and b=15 images, b=0 and b=20 images, b=0 and b=30 s/mm2 images, respectively. For liver simple cyst, two cysts totaling six slices scanned at 1.5T were available for DDVD measurement.

Results

At 1.5T, when the second b-value was 1 s/mm2, DDVDspleen value was slightly higher than DDVDliver value; when the second b-value was 2 s/mm2, DDVDliver value was slightly higher than DDVDspleen value. After that, the absolute difference between DDVDliver value and DDVDspleen value became increasingly larger, with DDVDliver value being consistently higher. DDVDcyst showed values close to 0 when the second b-value was 1 s/mm2. When the second b-value was 20 or 30 s/mm2, DDVDcyst value was higher than DDVDliver value. The absolute DDVD values measured higher at 3.0T than at 1.5T. However, the ratio of DDVDspleen to DDVDliver did not apparently differ between 1.5T and 3.0T. From the second b-value being 2 s/mm2 onward, an increasingly larger second b-value was associated with a trend of slow decreasing of the ratio of DDVDspleen to DDVDliver.

Conclusions

When a very low second b-value is applied, the liver and spleen measure similar perfusions by DDVD, and cysts measure DDVD close to zero. When a higher second b-value is applied, relative to the liver, the DDVD of spleen is suppressed while the DDVD of cyst is artificially promoted, which we consider are related to the T2 relaxation times of the liver, spleen, and cyst.

Variabilities in apparent diffusion coefficient (ADC) measurements of the spleen and the paraspinal muscle: A single center large cohort study

Purpose

Evaluation of the variabilities in apparent diffusion coefficient (ADC) measurements of the spleen (ADC_spleen) and the paraspinal muscles (ADC_muscle) to identify the reference organ for normalizing the ADC from the abdominal diffusion weighted imaging (DWI).

Methods

Two MRI scanners, with 314 abdominal exams on the GE and 929 on the Siemens system, were used for MRI examinations including DWI (b-values, 50 and 800 s/mm²). For a subset of 73 exams on the Siemens system a second exam was conducted. Four regions of interest (ROIs) in each exam were placed to measure the ADC_spleen and the bilateral ADC_muscle. ADC variability between patients (on each scanner separately), ADC variability due to ROI placement between the two ROIs in each organ, and variability in the subset between the first and second exams were assessed.

Results

The ADC_spleen was more scattered and variable than the ADC_muscle in the comparability (n = 929 and 314 for two MRI scanners, respectively) and repeatability (n = 73) datasets. The Bland-Altmann bias and limits of agreement (LoAs) for the ADC_spleen (ICC, 0.47; CV, 0.070) and ADC_muscle (ICC, 0.67; CV, 0.023) in the repeatability datasets (n = 73) were -0.1 (-25.7%-25.6%) and -0.3 (-8.8%-8.1%), respectively. For the Siemens system, the Bland-Altmann bias and LoAs for the ADC_spleen (ICC, 0.72; CV, 0.061) and ADC_muscle (ICC, 0.53; CV, 0.030) in the comparability datasets (n = 929) were 2.1 (-20.0%-24.2%) and 0.7 (-10.0%-11.4%), respectively. Similar findings have been found in the GE system (n = 314). The CVs for the ADC_muscle measurements were lower than those of the ADC_spleen both in the repeatability and the comparability analyses (all p < 0.001).

Conclusion

Paraspinal muscles demonstrate better reference characteristics than the spleen in estimating ADC variability of abdominal DWI.

Soy lecithin: A beneficial substance for adjusting the ADC in aqueous solutions to the values of biological tissues

PURPOSE

To test soy lecithin as a substance added to water for the construction of MRI phantoms with tissue-like diffusion coefficients. The performance of soy lecithin was assessed for the useable range of adjustable ADC values, the degree of non-Gaussian diffusion, simultaneous effects on relaxation times, and spectral signal properties.

METHODS

Aqueous soy lecithin solutions of different concentrations (0%, 0.5%, 1%, 2%, 3% …, 10%) and soy lecithin-agar gels were prepared and examined on a 3 Tesla clinical scanner at 18.5° ± 0.5°C. Echoplanar sequences (b values: 0-1000/3000 s/mm² ) were applied for ADC measurements. Quantitative relaxometry and MRS were performed for assessment of T₁ , T₂ , and detectable spectral components.

RESULTS

The presence of soy lecithin significantly restricts the diffusion of water molecules and mimics the nearly Gaussian nature of diffusion observed in tissue (for b values <1000 s/mm² ). ADC values ranged from 2.02 × 10^-3  mm² /s to 0.48 × 10^-3  mm² /s and cover the entire physiological range reported on biological tissue. Measured T₁ /T₂ values of pure lecithin solutions varied from 2685/2013 to 668/133 ms with increasing concentration. No characteristic signals of soy lecithin were observed in the MR spectrum. The addition of agar to the soy lecithin solutions allowed T₂ values to be well adjusted to typical values found in parenchymal tissue without affecting the soy lecithin-controlled ADC value.

CONCLUSION

Soy lecithin is a promising substance for the construction of diffusion phantoms with tissue-like ADC values. It provides several advantages over previously proposed substances, in particular a wide range of adjustable ADC values, the lack of additional ¹ H-signals, and the possibility to adjust ADC and T₂ values (by adding agar) almost independently of each other.

Evaluation of the Effects of Differences in Metal Artifact Type and Location on Image Quality in Computed Tomography Scans

Artifacts in computed tomography scans distort anatomical information and prevent an accurate diagnosis. Therefore, this study aims to determine the most effective method for reducing metal-induced artifacts by evaluating the effects of the metal artifact type and location, and the tube voltage on the image quality. Fe and Cu wires were inserted into a Virtual Water™ phantom at 6.5 and 11 cm distances from the center point (DPs). The contrast-to-noise ratios (CNRs) and signal-to-noise ratios (SNRs) were calculated to compare the images. The results reveal higher CNRs and SNRs when using standard and Smart metal artifact reduction (Smart MAR) algorithms for Cu and Fe insertions, respectively. The standard algorithm leads to a higher CNR and SNR for Fe and Cu at DPs of 6.5 and 11 cm, respectively. The Smart MAR algorithm provides effective outcomes at voltages of 100 and 120 kVp for wires located at 11 and 6.5 cm DP, respectively. The most effective imaging conditions for MAR is generated by the Smart MAR algorithm with a tube voltage for 100 kVp for Fe located at a DP of 11 cm. MAR can be improved by setting suitable tube voltage conditions according to the type and location of inserted metal.

Respiratory triggered diffusion-weighted imaging with a single diffusion sensitising gradient to reduce image acquisition time - A feasibility study in the workup of hepatocellular carcinoma

PURPOSE

We evaluated respiratory triggered unidirectional single-shot echo-planar imaging (u-SSEPI) as a time-saving measure in diffusion imaging of the upper abdomen. Specifically, we compared the ADC values obtained from unidirectional DWI (u-SSEPI) and routine DWI (4t-SSEPI) and also the diagnostic accuracies of unidirectional and routine DWI sequences in the identification of focal liver lesions in the setting of chronic liver disease (CLD).

MATERIALS AND METHODS

This prospective, IRB approved study, included 48 patients of CLD who underwent-DCE-MRI on a 1.5 T scanner for hepatocellular carcinoma (HCC) workup. In addition to 4t-SSEPI, u-SSEPI was acquired with the diffusion sensitising gradient being applied in only one direction; keeping all other parameters same as 4t-SSEPI. Two blinded radiologists evaluated the DWI studies for image quality and detection of liver lesions. A composite gold standard was established using DCE-MRI, follow-up imaging and patient clinical details. The apparent diffusion coefficients (ADCs) of the liver, spleen and the lesions were compared between the two sequences. ROC analysis evaluated the diagnostic accuracy of ADC from both the sequences in identifying HCC.

RESULTS

Eighty-eight lesions were identified using the composite gold standard. u-SSEPI resulted in 3 times faster image acquisition. No statistically significant differences were demonstrated between the unidirectional and routine DWI sequences for image quality parameters and lesion detection rates. Lesion wise comparison of the ADC values from both the sequences was not statistically different (p = 0.8) with a coefficient of variation = 12-14 %. The Bland- Altman plots and the Passing-Bablock regression analysis demonstrated a systematic and proportional bias between the ADC values obtained. The AUC of the ROC curve, however, was 0.63-observer1; 0.62-oobserver2 for routine DWI and 0.65; 0.62 for unidirectional DWI when ADC was used to identify HCC (the AUCs were not statistically different (p =  0.6-0.8)).

CONCLUSION

No significant differences were demonstrated in the diagnostic accuracies of unidirectional and routine DWI in the diagnosis of HCC. Unidirectional diffusion may be further evaluated in other organs where diffusion is isotropic, especially in respiratory triggered sequences where the imaging time dividend is significant.

Diffusion-Weighted Imaging for Differentiation of Biliary Atresia and Grading of Hepatic Fibrosis in Infants with Cholestasis

Objective

To determine whether the values of hepatic apparent diffusion coefficient (ADC) can differentiate biliary atresia (BA) from non-BA or be correlated with the grade of hepatic fibrosis in infants with cholestasis.

Materials and Methods

This retrospective cohort study included infants who received liver MRI examinations to evaluate cholestasis from July 2009 to October 2017. Liver ADC, ADC ratio of liver/spleen, aspartate aminotransferase to platelet ratio index (APRI), and spleen size were compared between the BA and non-BA groups. The diagnostic performances of all parameters for significant fibrosis (F3–4) were obtained by receiver-operating characteristics (ROCs) curve analysis.

Results

Altogether, 227 infants (98 males and 129 females, mean age = 57.2 ± 36.3 days) including 125 BA patients were analyzed. The absolute ADC difference between two reviewers was 0.10 mm²/s for both liver and spleen. Liver ADC value was specific (80.4%) and ADC ratio was sensitive (88.0%) for the diagnosis of BA with comparable performance. There were 33 patients with F0, 15 with F1, 71 with F2, 35 with F3, and 11 with F4. All four parameters of APRI (τ = 0.296), spleen size (τ = 0.312), liver ADC (τ = −0.206), and ADC ratio (τ = −0.288) showed significant correlation with fibrosis grade (all, p < 0.001). The cutoff values for significant fibrosis (F3–4) were 0.783 for APRI (area under the ROC curve [AUC], 0.721), 5.9 cm for spleen size (AUC, 0.719), 1.044 × 10⁻³ mm²/s for liver ADC (AUC, 0.673), and 1.22 for ADC ratio (AUC, 0.651).

Conclusion

Liver ADC values and ADC ratio of liver/spleen showed limited additional diagnostic performance for differentiating BA from non-BA and predicting significant hepatic fibrosis in infants with cholestasis.

Diagnostic test accuracy of ADC values for identification of clear cell renal cell carcinoma: systematic review and meta-analysis

OBJECTIVES

To perform a systematic review on apparent diffusion coefficient (ADC) values of renal tumor subtypes and meta-analysis on the diagnostic performance of ADC for differentiation of localized clear cell renal cell carcinoma (ccRCC) from other renal tumor types.

METHODS

Medline, Embase, and the Cochrane Library databases were searched for studies published until May 1, 2019, that reported ADC values of renal tumors. Methodological quality was evaluated. For the meta-analysis on diagnostic test accuracy of ADC for differentiation of ccRCC from other renal lesions, we applied a bivariate random-effects model and compared two subgroups of ADC measurement with vs. without cystic and necrotic areas.

RESULTS

We included 48 studies (2588 lesions) in the systematic review and 13 studies (1126 lesions) in the meta-analysis. There was no significant difference in ADC of renal parenchyma using b values of 0-800 vs. 0-1000 (p = 0.08). ADC measured on selected portions (sADC) excluding cystic and necrotic areas differed significantly from whole-lesion ADC (wADC) (p = 0.002). Compared to ccRCC, minimal-fat angiomyolipoma, papillary RCC, and chromophobe RCC showed significantly lower sADC while oncocytoma exhibited higher sADC. Summary estimates of sensitivity and specificity to differentiate ccRCC from other tumors were 80% (95% CI, 0.76-0.88) and 78% (95% CI, 0.64-0.89), respectively, for sADC and 77% (95% CI, 0.59-0.90) and 77% (95% CI, 0.69-0.86) for wADC. sADC offered a higher area under the receiver operating characteristic curve than wADC (0.852 vs. 0.785, p = 0.02).

CONCLUSIONS

ADC values of kidney tumors that exclude cystic or necrotic areas more accurately differentiate ccRCC from other renal tumor types than whole-lesion ADC values.

KEY POINTS

• Selective ADC of renal tumors, excluding cystic and necrotic areas, provides better discriminatory ability than whole-lesion ADC to differentiate clear cell RCC from other renal lesions, with area under the receiver operating characteristic curve (AUC) of 0.852 vs. 0.785, respectively (p = 0.02). • Selective ADC of renal masses provides moderate sensitivity and specificity of 80% and 78%, respectively, for differentiation of clear cell renal cell carcinoma (RCC) from papillary RCC, chromophobe RCC, oncocytoma, and minimal-fat angiomyolipoma. • Selective ADC excluding cystic and necrotic areas are preferable to whole-lesion ADC as an additional tool to multiphasic MRI to differentiate clear cell RCC from other renal lesions whether the highest b value is 800 or 1000.