Applicable apparent diffusion coefficient of an orthotopic mouse model of gastric cancer by improved clinical MRI diffusion weighted imaging

Association between the apparent diffusion coefficient and the preoperative chemotherapy response of patients with locally advanced gastric cancer

Background

The apparent diffusion coefficient is a parameter measured by magnetic resonance imaging (MRI). Studies in breast cancer and osteosarcoma have shown that the apparent diffusion coefficient has a good correlation with the efficacy of neoadjuvant chemotherapy. However, to date, no studies have evaluated the association between the apparent diffusion coefficient and the preoperative chemotherapy response of patients with locally advanced gastric cancer.

Methods

The data of 143 patients with locally advanced gastric cancer admitted to Zhejiang Medical and Health Group Quzhou Hospital (Zhejiang Quhua Hospital) from January 2018 to January 2019 were retrospectively collected. All the patients underwent preoperative chemotherapy and dynamic enhanced MRI to analyze the correlation between the apparent diffusion coefficient and preoperative chemotherapy response.

Results

Compared to the control group, the apparent diffusion coefficient of the objective remission group was significantly increased [(1.16±0.26) ×10^-3 vs. (0.95±0.26) ×10^-3 mm²/s, P<0.001]; the rate of the apparent diffusion coefficient >1.095×10^-3 mm²/s was significantly increased (61.29% vs. 30.00%, P<0.001). The apparent diffusion coefficient was valuable in predicting objective remission after preoperative chemotherapy in patients with locally advanced gastric cancer, the area under the curve (AUC) was 0.708 [95% confidence interval (CI): 0.621-0.796, P<0.001], the best diagnostic cut-off value was 1.095×10^-3 mm²/s, and the sensitivity and specificity were 0.613 and 0.700, respectively. The multivariate logistics regression analysis showed that the apparent diffusion coefficient of >1.095×10^-3 mm²/s was associated with the objective response of patients with locally advanced gastric cancer after preoperative chemotherapy [P=0.004, relative risk =3.135 (95% CI: 1.452-6.768)]. The apparent diffusion coefficient was valuable in predicting the non-recurrence of locally advanced gastric cancer patients, and the AUC was 0.647 (95% CI: 0.557-0.738, P=0.003). The apparent diffusion coefficient was also valuable in predicting the postoperative survival of patients with locally advanced gastric cancer, and the AUC was 0.630 (95% CI: 0.537-0.723, P=0.007).

Conclusions

The elevated apparent diffusion coefficient was associated with objective remission of the preoperative chemotherapy response and prognosis of patients with locally advanced gastric cancer.

Effective bowel motion reduction in mouse abdominal MRI using hyoscine butylbromide

PURPOSE

Bowel motion is a significant source of artifacts in mouse abdominal MRI. Fasting and administration of hyoscine butylbromide (BUSC) have been proposed for bowel motion reduction but with inconsistent results and limited efficacy assessments. Here, we evaluate these regimes for mouse abdominal MRI at high field.

METHODS

Thirty-two adult C57BL/6J mice were imaged on a 9.4T scanner with a FLASH sequence, acquired over 90 min with ~19 s temporal resolution. During MRI acquisition, 8 mice were injected with a low-dose and 8 mice with a high-dose bolus of BUSC (0.5 and 5 mg/kg, respectively). Eight mice were food deprived for 4.5-6.5 hours before MRI and another group of eight mice was injected with saline during MRI acquisition. Two expert readers reviewed the images and classified bowel motion, and quantitative voxel-wise analyses were performed for identification of moving regions. After defining the most effective protocol, high-resolution T₂ -weighted and diffusion-weighted images were acquired from 4 mice.

RESULTS

High-dose BUSC was the most effective protocol for bowel motion reduction, for up to 45 min. Fasting and saline protocols were not effective in suppressing bowel motion. High-resolution abdominal MRI clearly demonstrated improved image quality and ADC quantification with the high-dose BUSC protocol.

CONCLUSION

Our data show that BUSC administration is advantageous for abdominal MRI in the mouse. Specifically, it endows significant bowel motion reduction, with relatively short onset timings after injection (~8.5 min) and relatively long duration of the effect (~45 min). These features improve the quality of high-resolution images of the mouse abdomen.

Respiratory Motion Mitigation and Repeatability of Two Diffusion-Weighted MRI Methods Applied to a Murine Model of Spontaneous Pancreatic Cancer

Respiratory motion and increased susceptibility effects at high magnetic fields pose challenges for quantitative diffusion-weighted MRI (DWI) of a mouse abdomen on preclinical MRI systems. We demonstrate the first application of radial k-space-sampled (RAD) DWI of a mouse abdomen using a genetically engineered mouse model of pancreatic ductal adenocarcinoma (PDAC) on a 4.7 T preclinical scanner equipped with moderate gradient capability. RAD DWI was compared with the echo-planar imaging (EPI)-based DWI method with similar voxel volumes and acquisition times over a wide range of b-values (0.64, 535, 1071, 1478, and 2141 mm²/s). The repeatability metrics are assessed in a rigorous test-retest study (n = 10 for each DWI protocol). The four-shot EPI DWI protocol leads to higher signal-to-noise ratio (SNR) in diffusion-weighted images with persisting ghosting artifacts, whereas the RAD DWI protocol produces relatively artifact-free images over all b-values examined. Despite different degrees of motion mitigation, both RAD DWI and EPI DWI allow parametric maps of apparent diffusion coefficients (ADC) to be produced, and the ADC of the PDAC tumor estimated by the two methods are 1.3 ± 0.24 and 1.5 ± 0.28 × 10^-3 mm²/s, respectively (p = 0.075, n = 10), and those of a water phantom are 3.2 ± 0.29 and 2.8 ± 0.15 × 10^-3 mm²/s, respectively (p = 0.001, n = 10). Bland-Altman plots and probability density function reveal good repeatability for both protocols, whose repeatability metrics do not differ significantly. In conclusion, RAD DWI enables a more effective respiratory motion mitigation but lower SNR, while the performance of EPI DWI is expected to improve with more advanced gradient hardware.

Metabolic alterations in a rat model of hepatic ischaemia reperfusion injury: In vivo hyperpolarized 13 C MRS and metabolic imaging

BACKGROUND & AIMS

Despite a number of studies addressing the pathophysiology of hepatic IRI, a gold standard test for early diagnosis and evaluation of IRI remains elusive. This study investigated the metabolic alterations in a rat model of hepatic IRI using the in vivo hyperpolarized ¹³C MRS and metabolic imaging.

METHODS

Hyperpolarized ¹³ C MRS with IVIM-DWI was performed on the liver of 7 sham-operated control rats and 7 rats before and after hepatic IRI.

RESULTS

The hepatic IRI-induced rats showed significantly higher ratios of [1-¹³ C] alanine/pyruvate, [1-¹³ C] alanine/tC, [1-¹³ C] lactate/pyruvate and [1-¹³ C] lactate/tC compared with both sham-operated controls and rats before IRI, whereas [1-¹³ C] pyruvate/tC ratio was decreased in IRI-induced rats. In IVIM-DWI study, apparent diffusion coefficient (ADC), f and D values in rats after hepatic IRI were significantly lower than those of rats before IRI and sham-operated controls. The levels of [1-¹³ C] alanine and [1-¹³ C] lactate were negatively correlated with ADC, f and D values, whereas the level of [1-¹³ C] pyruvate was positively correlated with these values.

CONCLUSIONS

The levels of [1-¹³ C] alanine, [1-¹³ C] lactate and [1-¹³ C] pyruvate in conjunction with IVIM-DWI will be helpful to evaluate the hepatic IRI as well as these findings can be useful in understanding the biochemical mechanism associated with hepatic damage.