Multiparametric Magnetic Resonance Imaging for Assessing Thymic Epithelial Tumors: Correlation With Pathological Subtypes and Clinical Stages

BACKGROUND

World Health Organization classification and Masaoka-Koga stage are widely used for thymic epithelial tumors (TETs). Reduced field-of-view (rFOV) diffusion-weighed imaging (DWI) proved to improve the image quality. Dynamic contrast-enhanced (DCE) MRI was commonly used in evaluating tumors.

PURPOSE

To investigate the value of multiparametric MRI in evaluating TETs.

STUDY TYPE

Retrospective.

SUBJECTS

Eighty-seven participants including 38 low risk (52.08 ± 14.19 years), 30 high risk (52.40 ± 11.35 years), and 19 thymic carcinoma patients (59.76 ± 10.78 years).

FIELD STRENGTH/SEQUENCE

A 3 T, turbo spin echo imaging, echo planar imaging, volumetric interpolated breath-hold examination with radial acquisition trajectory.

ASSESSMENT

DCE-MRI and apparent diffusion coefficient (ADC) variables were compared. Diagnostic performances of single significant factor and combined model were compared.

STATISTICAL TESTS

Parameters were compared using one-way ANOVA or independent-samples t test. Logistic regression was employed to investigate the combined model. Receiver operating curves (ROC) and DeLong's test were used to compare the diagnostic efficiency.

RESULTS

ADC, K^trans , and k_ep values were significantly different among low-risk, high-risk and carcinoma group (ADC, 1.279 ± 0.345 × 10^-3  mm² /sec, 0.978 ± 0.260 × 10^-3  mm² /sec, 0.661 ± 0.134 × 10^-3  mm² /sec; K^trans 0.167 ± 0.071 min^-1 , 0.254 ± 0.136 min^-1 , 0.393 ± 0.110 min^-1 ; k_ep 0.345 ± 0.113 min^-1 , 0.560 ± 0.269 min^-1 , 0.872 ± 0.149 min^-1 ). They were significantly different for early stage and advanced stage (ADC, 1.270 ± 0.356 × 10^-3  mm² /sec vs. 0.845 ± 0.251 × 10^-3  mm² /sec; K^trans 0.179 ± 0.092 min^-1 vs. 0.304 ± 0.142 min^-1 ; k_ep 0.370 ± 0.181 min^-1 vs. 0.674 ± 0.362 min^-1 ). The combination of them had highest diagnostic efficiency for WHO classification (AUC, 0.925; sensitivity, 83.7%; specificity, 89.5%), clinical stage (AUC, 0.879; sensitivity, 80.9%; specificity, 82.5%).

DATA CONCLUSION

Multiparametric MRI model may be useful for discriminating WHO classification and clinical stage of TETs.

EVIDENCE LEVEL

4 TECHNICAL EFFICIENCY: Stage 2.

Placental perfusion in uterine ischemia model as evaluated by dynamic contrast enhanced MRI

BACKGROUND

To validate DCE MRI method of placental perfusion estimation and to demonstrate application of the method in a rabbit model of fetal antenatal hypoxia-ischemia.

METHODS

Placental perfusion was estimated by dynamic contrast imaging with bolus injection of Gd-DTPA in 3 Tesla GE magnet in a rabbit model of placental ischemia-reperfusion in rabbit dams at embryonic day 25 gestation age. Placental perfusion was measured using steepest slope method on DCE MRI before and after intermittent 40 min uterine ischemia. Antioxidants (n = 2 dams, 9 placentas imaged) or vehicle (n = 5 dams, 23 placenta imaged) were given systemically in a separate group of dams during reperfusion-reoxygenation. Placental perfusion was also measured in two dams from the antioxidant group (10 placentas) and two dams from the control group (12 placentas) by fluorescent microspheres method.

RESULTS

While placental perfusion estimates between fluorescent microspheres and DCE MRI were significantly correlated (R(2)  = 0.85; P < 0.01), there was approximately 33% systematic underestimation by the latter technique. DCE MRI showed a significant decrease in maternal placental perfusion in reperfusion-reoxygenation phase in the saline, 0.44 ± 0.06 mL/min/g (P = 0.012, t-test), but not in the antioxidant group, 0.62 ± 0.06 mL/min/g, relative to pre-occlusion values (0.77 ± 0.07 and 0.84 ± 0.12 mL/min/g, correspondingly).

CONCLUSION

Underestimation of true perfusion in placenta by steepest slope DCE MRI is significant and the error appears to be systematic.

Multiparametric magnetic resonance imaging in prostate cancer: present and future

PURPOSE OF REVIEW

The purpose of this article is to review the current status of advanced MRI techniques based on anatomic, metabolic and physiologic properties of prostate cancer with a focus on their impact in managing prostate cancer patients.

RECENT FINDINGS

Prostate cancer can be identified based on reduced T2 signal intensity on MRI, increased choline and decreased citrate and polyamines on magnetic resonance spectroscopic imaging (MRSI), decreased diffusivity on diffusion tensor imaging (DTI), and increased uptake on dynamic contrast enhanced (DCE) imaging. All can be obtained within a 60-min 3T magnetic resonance exam. Each complementary method has inherent advantages and disadvantages: T2 MRI has high sensitivity but poor specificity; magnetic resonance spectroscopic imaging has high specificity but poor sensitivity; diffusion tensor imaging has high spatial resolution, is the fastest, but sensitivity/specificity needs to be established; dynamic contrast enhanced imaging has high spatial resolution, but requires a gadolinium based contrast agent injection, and sensitivity/specificity needs to be established.

SUMMARY

The best characterization of prostate cancer in individual patients will most likely result from a multiparametric (MRI/MRSI/DTI/DCE) exam using 3T magnetic resonance scanners but questions remain as to how to analyze and display this large amount of imaging data, and how to optimally combine the data for the most accurate assessment of prostate cancer. Histological correlations or clinical outcomes are required to determine sensitivity/specificity for each method and optimal combinations of these approaches.