Andrew N. Priest

Semiquantitative and quantitative dynamic contrast-enhanced magnetic resonance imaging measurements predict radiation response in cervix cancer

PURPOSEnTo evaluate semiquantitative and quantitative dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) measurements in predicting the response to radiotherapy in cervix cancer.nnnMETHODS AND MATERIALSnPatients with cervix cancer treated radically with chemoradiotherapy had DCE-MRI at three time points: before starting treatment, after 2 weeks of radiotherapy, and in the 5th week of radiotherapy. Semiquantitative measurements obtained from the signal intensity vs. time plots included arrival time of contrast, the slope and maximum slope of contrast uptake, time for peak enhancement, and the contrast enhancement ratio (CER). Pharmacokinetic modeling with a modeled vascular input function was used for the quantitative measurements volume transfer constant (K(trans)), rate constant (k(ep)), fraction plasma volume (fPV), and the initial area under gadolinium-time curve. The correlation of these measurements at each of the three time points with radiologic tumor response was investigated.nnnRESULTSnThirteen patients had a total of 38 scans. There was no correlation between the DCE-MRI measurements and the corresponding tumor volumes. A statistically significant correlation with percentage tumor regression was shown with the pretreatment DCE-MRI semiquantitative parameters of peak time (p = 0.046), slope (p = 0.025), maximum slope (p = 0.046), and CER (p = 0.025) and the quantitative parameters K(trans) (p = 0.043) and k(ep) (p = 0.022). Second and third scan measurements did not show any correlation.nnnCONCLUSIONSnThis is the first study to show that pretreatment DCE-MRI quantitative parameters predict the radiation response in cervix cancer. These measurements may allow a more meaningful comparison of DCE-MRI studies from different centers.

Apparent diffusion coefficient and vascular signal fraction measurements with magnetic resonance imaging: feasibility in metastatic ovarian cancer at 3 Tesla

This prospective study aims to evaluate the feasibility of DWI at 3 Tesla in patients with advanced ovarian cancer and investigate the differences in vascular signal fraction (VSF) and apparent diffusion coefficient (ADC) values between primary ovarian mass and metastatic disease. Twenty patients with suspected advanced ovarian carcinoma were enrolled in the study. High-resolution T2W FRFSE images were used to confirm the position of three marker lesions: primary ovarian mass, omental cake and peritoneal deposit. Multislice DWI was acquired in a single breath-hold using multiple b-values. The three marker lesions were outlined by an experienced radiologist on ADC and VSF maps. Ovarian lesions showed the highest ADC values. The mean ADC value for peritoneal deposits was significantly lower than for both ovarian lesions (pu2009=u20090.03) and omental cake (pu2009=u20090.03). The VSF for omental cake was significantly higher than for ovarian lesions (pu2009=u20090.01) and peritoneal deposits (pu2009=u20090.04). There was a significant positive correlation between ADC and VSF for peritoneal deposits (pu2009=u20090.04). DWI in advanced ovarian cancer is feasible at 3 T. There are significant differences in baseline ADC and VSF values between ovarian cancer, omental cake and peritoneal deposits that may explain the mixed treatment response that occurs at different disease sites.

DCE and DW MRI in monitoring response to androgen deprivation therapy in patients with prostate cancer: a feasibility study.

Androgen deprivation therapy (ADT) is a key primary treatment for advanced and metastatic prostate cancer and is an important neoadjuvant before radiotherapy. We evaluated 3.0 T dynamic contrast‐enhanced MRI and diffusion‐weighted (DW) MRI in monitoring ADT response. Twenty‐three consecutive patients with prostate cancer treated by primary ADT were included. Imaging was performed at baseline and 3 months posttreatment with ADT. After 3 months therapy there was a significant reduction in all dynamic contrast‐enhanced MRI parameters measured in tumor regions of interest (Ktrans, kep, vp, IAUGC‐90); P < 0.001. Areas of normal‐appearing peripheral zone showed no significant change; P = 0.285–0.879. Post‐ADT, there was no significant change in apparent diffusion coefficient values in tumors, whilst apparent diffusion coefficient values significantly decreased in areas of normal‐appearing peripheral zone, from 1.786 × 10−3 mm2/s to 1.561 × 10−3 mm2/s; P = 0.007. As expected the median Prostate‐Specific Antigen (PSA) significantly reduced from 30 ng/mL to 1.5 ng/mL posttreatment, and median prostate volume dropped from 47.6 cm3 to 24.9 cm3; P < 0.001. These results suggest that dynamic contrast‐enhanced MRI and diffusion‐weighted MRI offer different information but that both could prove useful adjuncts to the anatomical information provided by T2‐weighted imaging. dynamic contrast‐enhanced as a marker of angiogenesis may help demonstrate ADT resistance and diffusion‐weighted imaging may be more accurate in determining presence of tumor cell death versus residual tumor. Magn Reson Med, 2012.

Magnetic resonance elastography: Feasibility of liver stiffness measurements in healthy volunteers at 3 T

AIMnTo demonstrate the feasibility of obtaining liver stiffness measurements with magnetic resonance elastography (MRE) at 3T in normal healthy volunteers using the same technique that has been successfully applied at 1.5 T.nnnMETHODS AND MATERIALSnThe study was approved by the local ethics committee and written informed consent was obtained from all volunteers. Eleven volunteers (mean age 35 ± 9 years) with no history of gastrointestinal, hepatobiliary, or cardiovascular disease were recruited. The magnetic resonance imaging (MRI) protocol included a gradient echo-based MRE sequence using a 60 Hz pneumatic excitation. The MRE images were processed using a local frequency estimation inversion algorithm to provide quantitative stiffness maps. Adequate image quality was assessed subjectively by demonstrating the presence of visible propagating waves within the liver parenchyma underlying the driver location. Liver stiffness values were obtained using manually placed regions of interest (ROI) outlining the liver margins on the gradient echo wave images, which were then mapped onto the corresponding stiffness image. The mean stiffness values from two adjacent sections were recorded.nnnRESULTSnEleven volunteers underwent MRE. The quality of the MRE images was adequate in all the volunteers. The mean liver stiffness for the group was 2.3 ± 0.38 kPa (ranging from 1.7-2.8 kPa).nnnCONCLUSIONSnThis preliminary work using MRE at 3T in healthy volunteers demonstrates the feasibility of liver stiffness evaluation at 3T without modification of the approach used at 1.5 T. Adequate image quality and normal MRE values were obtained in all volunteers. The obtained stiffness values were in the range of those reported for healthy volunteers in previous studies at 1.5 T. There was good interobserver reproducibility in the stiffness measurements.

Metabolic characterization of primary and metastatic ovarian cancer by 1H‐MRS in vivo at 3T

1H‐MRS was performed on 12 women (age range 45–72) with ovarian cancer of FIGO stage 3 or above using a 3T MRI system with an 8‐channel cardiac receive coil. Respiratory‐triggered PRESS‐localized spectra (TE = 144 ms) were obtained separately from an ovarian mass and from metastatic disease. Peak areas were quantified relative to unsuppressed water using LCModel and spectra were discarded if LCModel reported signal‐to‐noise ratio (SNR) < 3 or if no metabolites were reported with standard deviation (SD) < 30%. The cystic fraction of each voxel was estimated by thresholding T2‐weighted images, and this was used both to correct the reported metabolite concentrations and to calculate an expected SNR of choline using the measured SNR of water. Choline was detected in 10/12 primary tumors and 5/11 metastatic lesions (range 2.0–16.6 mM). Of the 8/23 failures, 7 had a predicted choline SNR < 2, confirming that the failure to detect choline could be explained by technical problems. Glycine was observed in one benign lesion. 1H‐MRS can be used to quantify choline in primary and metastatic masses in ovarian cancer, but the moderately high rate of failure to detect choline necessitates careful recording of data quality parameters to discriminate true from false negatives. Magn Reson Med, 2009.

The emerging role of diffusion-weighted MRI in prostate cancer management

A significant amount of research has focused on the role of diffusion-weighted MRI (DW-MRI) in the management of patients with prostate cancer. Although uncertainties remain, a clearer picture of where this technique fits into clinical practice is now available. A combination of DW-MRI and T2-weighted MRI (T2W-MRI) demonstrates improved accuracy for lesion detection and localization compared with T2W-MRI alone, and has been suggested as a tool to guide tissue biopsy. DW-MRI could also have roles in active surveillance, evaluating treatment efficacy, and predicting disease recurrence. Furthermore, DW-MRI offers the exciting possibility of gathering information about tumor characteristics and aggressiveness in a noninvasive manner. Validation in large prospective multicenter trials is critical if this technique is to be integrated into current management algorithms for prostate cancer.

Modelling DW-MRI data from primary and metastatic ovarian tumours.

AbstractObjectivesTo assess goodness-of-fit and repeatability of mono-exponential, stretched exponential and bi-exponential models of diffusion-weighted MRI (DW-MRI) data in primary and metastatic ovarian cancer.MethodsThirty-nine primary and metastatic lesions from thirty-one patients with stage III or IV ovarian cancer were examined before and after chemotherapy using DW-MRI with ten diffusion-weightings. The data were fitted with (a) a mono-exponential model to give the apparent diffusion coefficient (ADC), (b) a stretched exponential model to give the distributed diffusion coefficient (DDC) and stretching parameter (α), and (c) a bi-exponential model to give the diffusion coefficient (D), perfusion fraction (f) and pseudodiffusion coefficient (D*).ResultsCoefficients of variation, established from repeated baseline measurements, were: ADC 3.1xa0%, DDC 4.3xa0%, α 7.0xa0%, D 13.2xa0%, f 44.0xa0%, D* 165.1xa0%. The bi-exponential model was unsuitable in these data owing to poor repeatability. After excluding the bi-exponential model, analysis using Akaike Information Criteria showed that the stretched exponential model provided the better fit to the majority of pixels in 64xa0% of lesions.ConclusionsThe stretched exponential model provides the optimal fit to DW-MRI data from ovarian, omental and peritoneal lesions and lymph nodes in pre-treatment and post-treatment measurements with good repeatability.Key points• DW-MRI data in ovarian cancer show deviation from mono-exponential behaviourn • Parameters derived from the stretched exponential model showed good repeatability (CV 7xa0%)n • The bi-exponential model was unsuitable because of poor parameter repeatabilityn • The stretched exponential model showed comparable repeatability to the mono-exponential modeln • The extra parameter (α) provides scope for investigation of heterogeneity or response

Prostate cancer metabolite quantification relative to water in 1H-MRSI in vivo at 3 Tesla

1H magnetic resonance spectroscopic imaging was performed on 16 men with suspected prostate cancer using an 8‐channel external receive coil at 3 T. Choline and citrate (Cit) signals were measured in prostate lesions and normal‐appearing peripheral zone as identified on T2‐weighted images. Metabolites were quantified relative to unsuppressed water from a separately acquired magnetic resonance spectroscopic imaging dataset using LCModel. Validation experiments were also performed in a phantom containing physiological concentrations of choline, Cit, and creatine. In vitro, fair agreement between measured and true concentrations was observed, with the greatest discrepancy being a 35% underestimation of Cit. In vivo, one dataset was rejected for failure to meet the quality criterion of linewidth <15 Hz, and in 6 of 15 subjects, insufficient normal‐appearing peripheral zone tissue was identified for study. Lesions were found to have higher choline and choline/Cit, and lower Cit, than normal‐appearing peripheral zone. The smaller skew of data obtained using water normalization in comparison with metabolite ratios suggests potential usefulness in longitudinal tumor monitoring and in studies of treatment effects. Magn Reson Med, 2010.

Coronary vessel-wall and lumen imaging using radial k-space acquisition with MRI at 3 Tesla

This study investigates the feasibility of imaging the coronary lumen and vessel-wall, using MRI with a radial k-space trajectory at 3xa0T. Such radial trajectories offer the advantage of greater vessel sharpness than traditional Cartesian trajectories. This field strength offers an increased signal-to-noise ratio (SNR) compared with 1.5xa0T, which compensates for the slight SNR reduction due to the radial sequence. Images of the coronary lumen were acquired for seven healthy volunteers. In ten volunteers the vessel wall was scanned, with blood suppression using oblique-slab adiabatic re-inversion. Scans were performed during free breathing, using prospective respiratory navigator-gating. Coronary lumen scans had SNR of 16.0±1.9 and contrast-to-noise ratio (CNR) of 10.3±2.1, showing acceptable image quality. Vessel wall images showed good image quality, with mean SNR of 16.6±2.0/5.8±2.8/10.1±2.2 for vessel wall/lumen/epicardial fat. The wall-blood CNR was 10.7±2.7, and wall-fat CNR was 6.5±2.5. It is concluded that radial gradient-echo imaging at 3xa0T is a promising method for coronary vessel-wall imaging, and is also feasible for imaging the coronary lumen.

Magnetic resonance proton spectroscopy and diffusion weighted imaging of chick embryo brain in ovo.

Metabolic compensatory mechanisms may partly account for the decreased vulnerability to hypoxia observed in the developing brain. We used proton magnetic resonance spectroscopy and diffusion-weighted imaging to measure the cerebral concentrations of lactate and other metabolites, as well as the apparent diffusion coefficient (ADC) of tissue water, before, during and after hypoxia in anaesthetised chick embryos in ovo. Reducing the inspired oxygen concentration to 8% for 40 min caused a significant rise in both mean (+/-S.D.) lactate:creatine and alanine:creatine ratios from 0.58 (0.41) to 1.56 (0.56) and 0.14 (0.14) to 0.29 (0.17), respectively. Under similar hypoxic conditions, ADC did not change from a mean baseline value of 0.95 (0.09), but did fall to 0.40 (0.12) x 10(9) mm(2) s(-1) with further stepwise reductions in oxygenation. Moderate hypoxia increases lactate concentration in the developing chick brain without compromising cellular energy metabolism.