Gas challenge-blood oxygen level-dependent (GC-BOLD) MRI in the rat Novikoff hepatoma model

Navigator-based motion compensation for liver BOLD measurement with five-echo SAGE EPI and breath-hold task

PURPOSE

The purpose of this work is to apply multi-echo spin- and gradient-echo (SAGE) echo-planar imaging (EPI) combined with a navigator-based (NAV) prospective motion compensation method for a quantitative liver blood oxygen level dependent (BOLD) measurement with a breath-hold (BH) task.

METHODS

A five-echo SAGE sequence was developed to quantitatively measure T2 and T2* to depict function with sufficient signal-to-noise ratio, spatial resolution and sensitivity to BOLD changes induced by the BH task. To account for respiratory motion, a navigator was employed in the form of a single gradient-echo projection readout, located at the diaphragm along the inferior-superior direction. Prior to each transverse imaging slice of the spin-echo EPI-based readouts, navigator acquisition and fat suppression were incorporated. Motion data was obtained from the navigator and transmitted back to the sequence, allowing real-time adjustments to slice positioning. Six healthy volunteers and three patients with liver carcinoma were included in this study. Quantitative T2 and T2* were calculated at each time point of the BH task. Parameters of t value from first-level analysis using a general linear model and hepatovascular reactivity (HVR) of Echo1, T2 and T2* were calculated.

RESULTS

The motion caused by respiratory activity was successfully compensated using the navigator signal. The average changes of T2 and T2* during breath-hold were about 1% and 0.7%, respectively. With the help of NAV prospective motion compensation whole liver t values could be obtained without motion artifacts. The quantified liver T2 (34.7 ± 0.7 ms) and T2* (29 ± 1.2 ms) values agreed with values from literature. In healthy volunteers, the distribution of statistical t value and HVR was homogeneous throughout the whole liver. In patients with liver carcinoma, the distribution of t value and HVR was inhomogeneous due to metastases or therapy.

CONCLUSIONS

This study demonstrates the feasibility of using a NAV prospective motion compensation technique in conjunction with five-echo SAGE EPI for the quantitative measurement of liver BOLD with a BH task.

A Paradigm Shift in Primary Liver Cancer Therapy Utilizing Genomics, Molecular Biomarkers, and Artificial Intelligence

Primary liver cancer is the sixth most common cancer worldwide and the third leading cause of cancer-related death. Conventional therapies offer limited survival benefit despite improvements in locoregional liver-directed therapies, which highlights the underlying complexity of liver cancers. This review explores the latest research in primary liver cancer therapies, focusing on developments in genomics, molecular biomarkers, and artificial intelligence. Attention is also given to ongoing research and future directions of immunotherapy and locoregional therapies of primary liver cancers.

Tale of Two Cities: narrative review of oxygen

The human brain contributes 2% of the body weight yet receives 15% of cardiac output and demands a constant supply of oxygen (O ₂) and nutrients to meet its metabolic needs. Cerebral autoregulation is responsible for maintaining a constant cerebral blood flow that provides the supply of oxygen and maintains the energy storage capacity. We selected oxygen administration-related studies published between 1975-2021 that included meta-analysis, original research, commentaries, editorial, and review articles. In the present narrative review, several important aspects of the oxygen effects on brain tissues and cerebral autoregulation are discussed, as well the role of exogenous O ₂ administration in patients with chronic ischemic cerebrovascular disease: We aimed to revisit the utility of O ₂ administration in pathophysiological situations whether or not being advantageous. Indeed, a compelling clinical and experimental body of evidence questions the utility of routine oxygen administration in acute and post-recovery brain ischemia, as evident by studies in neurophysiology imaging. While O ₂ is still part of common clinical practice, it remains unclear whether its routine use is safe.

Oxygen-Challenge Blood Oxygen Level-Dependent Magnetic Resonance Imaging for Evaluation of Early Change of Hepatocellular Carcinoma to Chemoembolization: A Feasibility Study

RATIONALE AND OBJECTIVES

To investigate the feasibility of oxygen-challenge blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) at 3T for evaluating the early change of blood oxygenation before and after transcatheter arterial embolization (TACE) in patients with hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Thirty HCC patients with cirrhosis (HCC group, n = 30) and 30 healthy volunteers (control group, n = 30) were included in this study. Patients in the HCC group underwent BOLD before and 1 month after TACE. Oxygen was administered via a mask. Differences between pre- and post-O₂ T₂* values were evaluated using a pairwise t-test. Analysis of variance was performed to assess the statistical differences in the T₂* values measured in HCC group pre-TACE and post-TACE and in healthy volunteers.

RESULTS

In the HCC group, the pre- and post-O₂ T₂* values of the cancerous area before TACE were 26.03 ± 3.30 and 26.84 ± 3.42 msec, respectively, and both decreased significantly to 8.67 ± 1.76 and 8.82 ± 1.80 msec, respectively, at 1 month after TACE (p < 0.001). The respective pre- and post-O₂ T₂* values of the noncancerous area increased significantly from 14.96 ± 2.32 and 15.33 ± 2.28 msec at baseline to 16.38 ± 2.22 and 16.89 ± 2.24 msec at 1 month after TACE (p < 0.001). No significant response to BOLD was observed in the control group (p = 0.059).

CONCLUSION

Oxygen-challenge BOLD MRI is feasible to assess post-TACE changes in HCC patients.

Yttrium-90 Radioembolization and Tumor Hypoxia: Gas-challenge BOLD Imaging in the VX2 Rabbit Model of Hepatocellular Carcinoma

RATIONALE AND OBJECTIVES

To use a rapid gas-challenge blood oxygen-level dependent magnetic resonance imaging exam to evaluate changes in tumor hypoxia after ⁹⁰Y radioembolization (Y90) in the VX2 rabbit model.

MATERIALS AND METHODS

White New Zealand rabbits (n = 11) provided a Y90 group (n = 6 rabbits) and untreated control group (n = 5 rabbits). R2* maps were generated with gas-challenges (O₂/room air) at baseline, 1 week, and 2 weeks post-Y90. Laboratory toxicity was evaluated at baseline, 24 hours, 72 hours, 1 hours, and 2 weeks. Histology was used to evaluate tumor necrosis on hematoxylin and eosin and immunofluorescence imaging was used to assess microvessel density (CD31) and proliferative index (Ki67).

RESULTS

At baseline, median tumor volumes and time to imaging were similar between groups (p = 1.000 and p = 0.4512, respectively). The median administered dose was 50.4 Gy (95% confidence interval:44.8-55.9). At week 2, mean tumor volumes were 5769.8 versus 643.7 mm³ for control versus Y90 rabbits, respectively (p = 0.0246). At two weeks, ΔR2* increased for control tumors to 12.37 ± 12.36sec^-1 and decreased to 4.48 ± 9.00sec^-1 after Y90. The Pearson correlation coefficient for ΔR2* at baseline and percent increase in tumor size by two weeks was 0.798 for the Y90 group (p = 0.002). There was no difference in mean microvessel density for control versus Y90 treated tumors (p = 0.6682). The mean proliferative index was reduced in Y90 treated tumors at 30.5% versus 47.5% for controls (p = 0.0071).

CONCLUSION

The baseline ΔR2* of tumors prior to Y90 may be a predictive imaging biomarker of tumor response and treatment of these tumors with Y90 may influence tumor oxygenation over time.

Treatment margins in radiotherapy for liver tumors visualized as T2*-hypointense areas on SPIO-enhanced MRI at 9.4 T

OBJECTIVE

To investigate whether a SPIO-labeling technique could enable MR visualization of the treatment margin after X-irradiation at a single dose of 30 Gy.

MATERIALS AND METHODS

Fifteen rats bearing N1-S1 hepatoma in either the left (group 1) or right (group 2) liver lobe were examined. Four hours after systemic SPIO administration, the left lobe was selectively irradiated at 30 Gy. Liver T2* maps were acquired 7 days later using a 9.4 T scanner. The livers were excised and examined histologically.

RESULTS

The irradiated area showed T2*-weighted hypointensity with significantly shorter T2* values than those in the non-irradiated area (p < 0.001). Tumors in group 1 completely disappeared, whereas tumors in group 2 had grown outside the T2*-weighted hypointensity by up to ~ 2.3 times that at baseline. Group 1 showed significantly higher probability of tumor regression than group 2 (p = 0.048). Histologically, iron deposition was heavier in irradiated areas than in non-irradiated areas.

DISCUSSION

Even at a single dose of 30 Gy, which is a slightly higher dose than can be used clinically in stereotactic body radiotherapy, MR visualization of the treatment margin was achieved, because tumors showed significant growth outside the T2*-hypointense areas. In contrast, tumors disappeared inside the T2*-hypointense areas.

Persistent T2*-hypointensity of the liver parenchyma after irradiation to the SPIO-accumulated liver: An imaging marker for responses to radiotherapy in hepatic malignancies

PURPOSE

To determine whether T2*-weighted MRI has the ability to visualize the irradiated liver parenchyma and liver tumor after irradiation to the previously superparamagnetic iron oxide (SPIO)-accumulated liver.

MATERIALS AND METHODS

We examined 24 liver tumor-bearing rats. Nine rats (Group 1) received 20 µmol Fe/kg SPIO and subsequent 70-Gy irradiation to the tumor-bearing liver lobe. Four rats (Group 2) received SPIO and sham irradiation. Six rats (Group 3) received saline and irradiation. Finally, five rats (Group 4) received saline and sham irradiation. We acquired sequential 3 Tesla T2*-weighted images of the liver on day 7, and assessed MR image findings including signal intensity of the tumors and tumor-bearing liver lobes.

RESULTS

In six rats in Group 1, tumors shrunk by 39-100% (303-0 mm³ ), and severely, well-defined hypointense irradiated areas were observed. In the other two rats, tumors enlarged by 25 and 172% (595 and 1148 mm³ ), and hypointense rings surrounded the tumors. The normalized relative signal intensity of the irradiated areas was significantly lower than that of the tumor (0.53 ± 0.06 versus 0.94 ± 0.06; P < 0.05). The severely, well-defined hypointense areas were not observed in the other groups. Histologically, necrotic regions dominated and minimal nonnecrotic tumor cells remained in irradiated areas. The number of CD68-positive cells was higher in irradiated areas than in nonirradiated areas.

CONCLUSION

T2*-weighted MR imaging visualized the irradiated liver parenchyma as markedly, well-defined hypointense areas and liver cancer lesions as hyperintense areas only when SPIO was administered before irradiation. The visualization of the hypointense area was associated with tumor regression after irradiation.

LEVEL OF EVIDENCE

2 J. Magn. Reson. Imaging 2017;45:303-312.

Comparison of tumor vascularity and hemodynamics in three rat hepatoma models

PURPOSE

To compare tumor vascularity and hemodynamics in three rat hepatoma models: N1-S1 cells in Sprague-Dawley rats, McA-RH7777 cells in Sprague-Dawley rats, and 13762 MAT B III cells in F344 rats.

METHODS

The three rat hepatoma models were induced in five rats per group. After confirming that the tumors grew up to 10 mm on magnetic resonance imaging, the rats underwent dynamic contrast-enhanced ultrasonography (DCE-US). Afterward, the rats were euthanized for histologic analyses. The Kruskal-Wallis test was used to compare the rat hepatoma models. Correlation coefficients were calculated between the microvessel density (MVD) and DCE-US parameters.

RESULTS

On DCE-US imaging, arterial enhancement and washout were demonstrated in all N1-S1 tumors, while persistent peripheral enhancement on arterial to portal phases was shown in all 13762 MAT B III tumors. The McA-RH7777 tumors presented diverse enhancement patterns on arterial and portal phases. There were no significant differences in DCE-US parameters among the three hepatoma groups, while MVD was correlated with peak intensity (r = 0.565, p = 0.044), mean transit time (r = -0.559, p = 0.047), and time to peak (r = - 0.617, p = 0.025) of individual rats. The necrosis ratio was significantly different between the models (p = 0.031); 13762 MAT B III showed a significantly higher necrosis ratio than N1-S1 (p < 0.050 by post hoc test).

CONCLUSION

The N1-S1 tumor may be suitable as a model to investigate hypervascular hepatic tumors of the liver in DCE-US such as hepatocellular carcinoma among the three tumors.

Feasibility and reproducibility of BOLD and TOLD measurements in the liver with oxygen and carbogen gas challenge in healthy volunteers and patients with hepatocellular carcinoma

PURPOSE

To quantify baseline relaxation rates R2* and R1 in the abdomen, their changes after respiratory challenges, and their reproducibility in healthy volunteers and patients with hepatocellular carcinoma (HCC) at 1.5T and 3.0T.

MATERIALS AND METHODS

R2* measurements were acquired in the liver in 8 volunteers and 27 patients with 34 HCCs using multiecho T2* at baseline and after respiratory challenges with 100% oxygen (O2 ) and carbogen (CB = 95%O2 /5%CO2 ). R1 was measured at 1.5T in one volunteer and 21 patients with 23 HCCs. Test-retest coefficient of variation (CV) was assessed in 10 subjects. Intra- and interobserver variability of R2* and R1 measurements was assessed in 12 and 10 patients, respectively. Parameters for HCC, liver, and muscle were compared between baseline and after gas challenges.

RESULTS

We observed that R2* and R1 imaging of HCCs with O2 and CB is feasible and reproducible (test-retest CV R2*<15%/R1 <5%; intra- and interobserver intraclass correlation coefficient R2*>0.88/R1 >0.7 and CV R2*<7%/R1 <3% at 1.5T). R2* measurements were observed to be less reproducible at 3.0T (CV<35%). There was a statistically significant decrease in R2* values in HCC before and after O2 (P = 0.02) and increase in R1 after O2 (P = 0.004). CB had no significant effect (P R2* = 0.47/R1  = 0.278).

CONCLUSION

R2* measurements in HCC and liver parenchyma are more reproducible at 1.5T than at 3.0T, and with O2 than with CB challenge. We observed a decrease in R2* and an increase in R1 of HCCs from baseline in response to O2 challenge, as expected with increased tissue and blood oxygenation.

Carbogen gas-challenge blood oxygen level-dependent magnetic resonance imaging in hepatocellular carcinoma: Initial results

The present study aimed to evaluate the feasibility of performing carbogen gas-challenge blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) measurements in patients with hepatocellular carcinoma (HCC). A total of 25 patients with HCC underwent T2* mapping derived from multi-echo gradient-recalled echo imaging prior to and following breathing carbogen (95% O₂ and 5% CO₂) for 10 min. Follow-up T2* mapping was performed in 5 patients 1 day after transarterial chemoembolization (TACE). T2*, R2* and ∆R2* values (R2*air - R2*carb) of the whole tumor, the solid region of the tumor and the adjacent liver parenchyma were measured and compared in the patients with HCC. The T2* value of the solid region of the tumor following carbogen breathing was higher than the value following room air breathing (P<0.05), and the R2* value of room air breathing was higher than that following carbogen breathing (P<0.05). ∆R2* values of the tumor and the adjacent liver parenchyma prior to and following carbogen breathing were 2.4±7.8, 8.1±14.7 and 2.0±11.0 sec⁻¹, respectively. R2* values were significantly decreased in 2 cases 1 day after TACE (17.8 vs. −3.4 sec⁻¹ and 10.2 vs. 2.4 sec⁻¹). Overall, carbogen gas-challenge BOLD MRI measurements are feasible in clinical settings and may serve as a novel functional biomarker for monitoring the treatment efficacy of embolic therapies for HCC.

Spontaneous tumor regression in a syngeneic rat model of liver cancer: implications for survival studies

PURPOSE

To characterize tumor growth of N1S1 cells implanted into the liver of Sprague-Dawley rats to determine if this model could be used for survival studies. These results were compared with tumor growth after implantation with McA-RH7777 cells.

MATERIALS AND METHODS

N1S1 or McA-RH7777 cells were implanted into the liver of Sprague-Dawley rats (n = 20 and n = 12, respectively) using ultrasound (US) guidance, and tumor growth was followed by using US. Serum profiles of 19 cytokines were compared in naive versus tumor-bearing rats.

RESULTS

Both types of tumors were visible on US 1 week after tumor implantation, but the mean tumor volume of N1S1 tumors was larger compared to McA-RH7777 tumors (231 mm(3) vs 82.3 mm(3), respectively). Tumor volumes in both groups continued to increase, reaching means of 289 mm(3) and 160 mm(3) in N1S1 and McA-RH7777 groups, respectively, 2 weeks after tumor implantation. By week 3, tumor volumes had decreased considerably, and six tumors (50%) in the McA-RH7777 had spontaneously regressed, versus two (10%) in the N1S1 group. Tumor volumes continued to decrease over the following 3 weeks, and complete tumor regression of all tumors was seen 5 weeks and 6 weeks after tumor implantation in the McA-RH7777 and N1S1 groups, respectively. In an N1S1-implanted rat, multiple cytokines that have been shown to correlate with the ability of the tumor to survive in a hostile environment were increased by as much as 50%, whereas the average increase in cytokine levels was 90%. These findings suggest that the net cytokine environment favors an antitumor immune response. A similar trend was observed in a rat with a McA-RH7777 tumor, and the increase in cytokine levels was considerably more pronounced, with an average increase of 320%.

CONCLUSIONS

The model of N1S1 cell implantation in the liver of Sprague-Dawley rats is not ideal for survival studies and should only be used with great caution in short-term studies that involve cancer therapies.