Added value of breathhold diffusion‐weighted MRI in detection of small hepatocellular carcinoma lesions compared with dynamic contrast‐enhanced MRI alone using receiver operating characteristic curve analysis

Purpose

To evaluate the added value of single‐breathhold diffusion‐weighted MRI (DWI) in detection of small hepatocellular carcinoma (HCC) lesions (≤2 cm) in patients with chronic liver disease, by comparing the detection sensitivity of combined DWI/conventional dynamic contrast‐enhanced (DCE)‐MRI to that of conventional DCE‐MRI alone.

Materials and Methods

A total of 37 patients with chronic liver diseases underwent abdominal MRI at 1.5T, including T1‐weighted imaging (T1WI), T2‐weighted imaging (T2WI), and 2D conventional DCE. For each patient study, axial DWI was performed with a single‐shot echo‐planar imaging (EPI) sequence using a modified sensitivity‐encoding (mSENSE) technique with b‐value of 500 seconds/mm². A total of 20–24 slices were obtained during a 15–17‐second breathhold. Two observers independently interpreted the combined DWI/conventional DCE‐MRI images and the conventional DCE‐MRI images alone in random order. For all small HCC lesions, the diagnostic performance using each imaging set was evaluated by receiver operating characteristic (ROC) curve analysis. Sensitivity and positive predictive values were also calculated and analyzed.

Results

A total of 47 small HCCs were confirmed as final result. The area under the ROC curve (Az) of combined DWI/conventional DCE‐MRI images (observer 1, 0.922; observer 2, 0.918) were statistically higher than those of conventional DCE‐MRI alone (observer 1, 0.809; observer 2, 0.778) for all small HCC lesions (P < 0.01). The lesion detection sensitivities using the combined technique for both observers were significantly higher than those using conventional DCE‐MRI alone (P < 0.01). The sensitivity values for two observers using the combined technique were 97.87% and those using conventional DCE‐MRI alone were 85.11% to 82.98%. The positive predictive values for two observers using the combined imaging technique (97.87%) were slightly higher than those using conventional DCE‐MRI alone (92.86–93.02%), but there was no significant difference between the two imaging sets.

Conclusion

Combined use of breathhold DWI with conventional DCE‐MRI helped to provide higher sensitivities than conventional DCE‐MRI alone in the detection of small HCC lesions in patients with chronic liver disease. J. Magn. Reson. Imaging 2009;29:341–349. © 2009 Wiley‐Liss, Inc.     

T2‐weighted MRI of post‐infarct myocardial edema in mice

T₂‐weighted, cardiac magnetic resonance imaging (T₂w CMR) can be used to noninvasively detect and quantify the edematous region that corresponds to the area at risk (AAR) following myocardial infarction (MI). Previously, CMR has been used to examine structure and function in mice, expediting the study of genetic manipulations. To date, CMR has not been applied to imaging of post‐MI AAR in mice. We developed a whole‐heart, T₂w CMR sequence to quantify the AAR in mouse models of ischemia and infarction. The ΔB₀ and ΔB₁ environment around the mouse heart at 7 T were measured, and a T₂‐preparation sequence suitable for these conditions was developed. Both in vivo T₂w and late gadolinium enhanced CMR were performed in mice after 20‐min coronary occlusions, resulting in measurements of AAR size of 32.5 ± 3.1 (mean ± SEM)% left ventricular mass, and MI size of 50.1 ± 6.4% AAR size. Excellent interobserver agreement and agreement with histology were also found. This T₂w imaging method for mice may allow for future investigations of genetic manipulations and novel therapies affecting the AAR and salvaged myocardium following reperfused MI. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Comparison of amyloid plaque contrast generated by T2‐weighted,T‐weighted,and susceptibility‐weighted imaging methods in transgenic mouse models of Alzheimer's disease

One of the hallmark pathologies of Alzheimer's disease (AD) is amyloid plaque deposition. Plaques appear hypointense on T₂‐weighted and T‐weighted MR images probably due to the presence of endogenous iron, but no quantitative comparison of various imaging techniques has been reported. We estimated the T₁, T₂, T, and proton density values of cortical plaques and normal cortical tissue and analyzed the plaque contrast generated by a collection of T₂‐weighted, T‐weighted, and susceptibility‐weighted imaging (SWI) methods in ex vivo transgenic mouse specimens. The proton density and T₁ values were similar for both cortical plaques and normal cortical tissue. The T₂ and T values were similar in cortical plaques, which indicates that the iron content of cortical plaques may not be as large as previously thought. Ex vivo plaque contrast was increased compared to a previously reported spin‐echo sequence by summing multiple echoes and by performing SWI; however, gradient echo and SWI were found to be impractical for in vivo imaging due to susceptibility interface–related signal loss in the cortex. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Prostate cancer detection with 3 T MRI: Comparison of diffusion‐weighted imaging and dynamic contrast‐enhanced MRI in combination with T2‐weighted imaging

Purpose:

To evaluate the diagnostic ability of diffusion‐weighted imaging (DWI) and dynamic contrast‐enhanced imaging (DCEI) in combination with T2‐weighted imaging (T2WI) for the detection of prostate cancer using 3 T magnetic resonance imaging (MRI) with a phased‐array body coil.

Materials and Methods:

Fifty‐three patients with elevated serum levels of prostate‐specific antigen (PSA) were evaluated by T2WI, DWI, and DCEI prior to needle biopsy. The obtained data from T2WI alone (protocol A), a combination of T2WI and DWI (protocol B), a combination T2WI and DCEI (protocol C), and a combination of T2WI plus DWI and DCEI (protocol D) were subjected to receiver operating characteristic (ROC) curve analysis.

Results:

The sensitivity, specificity, accuracy, and area under the ROC curve (Az) for region‐based analysis were: 61%, 91%, 84%, and 0.8415, respectively, in protocol A; 76%, 94%, 90%, and 0.8931, respectively, in protocol B; 77%, 93%, 89%, and 0.8655, respectively, in protocol C; and 81%, 96%, 92%, and 0.8968, respectively in protocol D. ROC analysis revealed significant differences between protocols A and B (P = 0.0008) and between protocols A and D (P = 0.0004).

Conclusion:

In patients with elevated PSA levels the combination of T2WI, DWI, DCEI using 3 T MRI may be a reasonable approach for the detection of prostate cancer. J. Magn. Reson. Imaging 2010;31:625–631. © 2010 Wiley‐Liss, Inc.     

FASCINATE: A pulse sequence for simultaneous acquisition of T2‐weighted and fluid‐attenuated images

A pulse sequence that enables simultaneous acquisition of T₂‐weighted and fluid‐attenuated images is presented. This sequence is referred to as FASCINATE (Fluid‐Attenuated Scan Combined with Interleaved Non‐ATtEnuation). In this new technique, the inversion pulse of conventional fast fluid‐attenuated inversion recovery (FLAIR) is replaced with a fast spin echo (FSE) acquisition that has an additional 180(y)–90(x) pulse train for driven inversion. By using appropriate scan parameters, the first part of the sequence provides T₂‐weighted images and the second part provides fluid‐attenuated images, thus allowing simultaneous acquisition in a single scan time comparable to that of fast FLAIR. FASCINATE was compared with conventional scanning techniques using a normal volunteer and a patient. A signal simulation was also conducted. In the human study, both T₂‐weighted and fluid‐attenuated images from FASCINATE showed the same image quality as conventional images, suggesting the potential for this technique to replace the combination of fast FLAIR and T₂‐weighted FSE for scan time reduction. Magn Reson Med 51:205–211, 2004. © 2003 Wiley‐Liss, Inc.     

Differential diagnosis of mammographically and clinically occult breast lesions on diffusion‐weighted MRI

Purpose:

To investigate the diagnostic performance of diffusion‐weighted imaging (DWI) for mammographically and clinically occult breast lesions.

Materials and Methods:

The study included 91 women with 118 breast lesions (91 benign, 12 ductal carcinoma in situ [DCIS], 15 invasive carcinoma) initially detected on dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) and assigned BI‐RADS category 3, 4, or 5. DWI was acquired with b = 0 and 600 s/mm². Lesion visibility was assessed on DWI. Apparent diffusion coefficient (ADC) values were compared between malignancies, benign lesions, and normal (no abnormal enhancement on DCE‐MRI) breast tissue, and the diagnostic performance of DWI was assessed based on ADC thresholding.

Results:

Twenty‐four of 27 (89%) malignant and 74/91 (81%) benign lesions were hyperintense on the b = 600 s/mm² diffusion‐weighted images. Both DCIS (1.33 ± 0.19 × 10^?3 mm²/s) and invasive carcinomas (1.30 ± 0.27 × 10^?3mm²/s) were lower in ADC than benign lesions (1.71 ± 0.43 × 10^?3mm²/s; P < 0.001), and each lesion type was lower in ADC than normal tissue (1.90 ± 0.38 × 10^?3mm²/s, P ≤ 0.001). Receiver operating curve (ROC) analysis showed an area under the curve (AUC) of 0.77, and sensitivity = 96%, specificity = 55%, positive predictive value (PPV) = 39%, and negative predictive value (NPV) = 98% for an ADC threshold of 1.60 × 10^?3mm²/s.

Conclusion:

Many mammographically and clinically occult breast carcinomas were visibly hyperintense on diffusion‐weighted images, and ADC enabled differentiation from benign lesions. Further studies evaluating DWI while blinded to DCE‐MRI are necessary to assess the potential of DWI as a noncontrast breast screening technique. J. Magn. Reson. Imaging 2010;1:562–570. © 2010 Wiley‐Liss, Inc.

     

Parallel‐transmission‐enabled three‐dimensional T2‐weighted imaging of the human brain at 7 Tesla

Purpose: A promise of ultra high field MRI is to produce images of the human brain with higher spatial resolution due to an increased signal to noise ratio. Yet, the shorter radiofrequency wavelength induces an inhomogeneous distribution of the transmit magnetic field and thus challenges the applicability of MRI sequences which rely on the spin excitation homogeneity. In this work, the ability of parallel‐transmission to obtain high‐quality T₂‐weighted images of the human brain at 7 Tesla, using an original pulse design method is evaluated. Methods: Excitation and refocusing square pulses of a SPACE sequence were replaced with short nonselective transmit‐SENSE pulses individually tailored with the gradient ascent pulse engineering algorithm, adopting a k_T‐point trajectory to simultaneously mitigate B₁⁺ and ΔB₀ nonuniformities. Results: In vivo experiments showed that exploiting parallel‐transmission at 7T with the proposed methodology produces high quality T₂‐weighted whole brain images with uniform signal and contrast. Subsequent white and gray matter segmentation confirmed the expected improvements in image quality. Conclusion: This work demonstrates that the adopted formalism based on optimal control, combined with the k_T‐point method, successfully enables three‐dimensional T₂‐weighted brain imaging at 7T devoid of artifacts resulting from B₁⁺ inhomogeneity. Magn Reson Med 73:2195–2203, 2015. © 2014 Wiley Periodicals, Inc.     

B1 transmission‐field inhomogeneity and enhancement ratio errors in dynamic contrast‐enhanced MRI (DCE‐MRI) of the breast at 3T

Purpose:

To quantify B₁ transmission‐field inhomogeneity in breast imaging of normal volunteers at 3T using 3D T₁‐weighted spoiled gradient echo and to assess the resulting errors in enhancement ratio (ER) measured in dynamic contrast‐enhanced MRI (DCE‐MRI) studies of the breast.

Materials and Methods:

A total of 25 volunteers underwent breast imaging at 3T and the B₁ transmission‐fields were mapped. Gel phantoms that simulate pre‐ and postcontrast breast tissue T₁ were developed. The effects of B₁‐field inhomogeneity on ER, as measured using a 3D spoiled gradient echo sequence, were investigated by computer simulation and experiments on gel phantoms.

Results:

It was observed that by using the patient orientation and MR scanner employed in this study, the B₁ transmission‐field field is always reduced toward the volunteer's right side. The median B₁‐field in the right breast is reduced around 40% of the expected B₁‐field. For some volunteers the amplitude was reduced by more than 50%. Computer simulation and experiment showed that a reduction in B₁‐field decreases ER. This reduction increases with both B₁‐field error and contrast agent uptake.

Conclusion:

B₁ transmission‐field inhomogeneity is a critical issue in breast imaging at 3T and causes errors in quantifying ER. These errors would be sufficient to reduce the conspicuity of a malignant lesion and could result in reduced sensitivity for cancer detection. J. Magn. Reson. Imaging 2010;31:234–239. © 2009 Wiley‐Liss, Inc.     

Prostate cancer detection with multi‐parametric MRI: Logistic regression analysis of quantitative T2, diffusion‐weighted imaging,and dynamic contrast‐enhanced MRI

Purpose

To develop a multi‐parametric model suitable for prospectively identifying prostate cancer in peripheral zone (PZ) using magnetic resonance imaging (MRI).

Materials and Methods

Twenty‐five radical prostatectomy patients (median age, 63 years; range, 44–72 years) had T2‐weighted, diffusion‐weighted imaging (DWI), T2‐mapping, and dynamic contrast‐enhanced (DCE) MRI at 1.5 Tesla (T) with endorectal coil to yield parameters apparent diffusion coefficient (ADC), T2, volume transfer constant (K^trans) and extravascular extracellular volume fraction (v_e). Whole‐mount histology was generated from surgical specimens and PZ tumors delineated. Thirty‐eight tumor outlines, one per tumor, and pathologically normal PZ regions were transferred to MR images. Receiver operating characteristic (ROC) curves were generated using all identified normal and tumor voxels. Step‐wise logistic‐regression modeling was performed, testing changes in deviance for significance. Areas under the ROC curves (A_z) were used to evaluate and compare performance.

Results

The best‐performing single‐parameter was ADC (mean A_z [95% confidence interval]: A_z,ADC: 0.689 [0.675, 0.702]; A_z,T2: 0.673 [0.659, 0.687]; A_z,Ktrans: 0.592 [0.578, 0.606]; A_z,ve: 0.543 [0.528, 0.557]). The optimal multi‐parametric model, LR‐3p, consisted of combining ADC, T2 and K^trans. Mean A_z,LR‐3p was 0.706 [0.692, 0.719], which was significantly higher than A_z,T2, A_z,Ktrans, and A_z,ve (P < 0.002). A_z,LR‐3p tended to be greater than A_z,ADC, however, this result was not statistically significant (P = 0.090).

Conclusion

Using logistic regression, an objective model capable of mapping PZ tumor with reasonable performance can be constructed. J. Magn. Reson. Imaging 2009;30:327–334. © 2009 Wiley‐Liss, Inc.     

Tracer kinetic analysis of dynamic contrast‐enhanced MRI and CT bladder cancer data: A preliminary comparison to assess the magnitude of water exchange effects

The purpose of this study was to determine the impact of water exchange on tracer kinetic parameter estimates derived from T₁‐weighted dynamic contrast‐enhanced (DCE)‐MRI data using a direct quantitative comparison with DCE‐CT. Data were acquired from 12 patients with bladder cancer who underwent DCE‐CT followed by DCE‐MRI within a week. A two‐compartment tracer kinetic model was fitted to the CT data, and two versions of the same model with modifications to account for the fast exchange and no exchange limits of water exchange were fitted to the MR data. The two‐compartment tracer kinetic model provided estimates of the fractional plasma volume (v_p), the extravascular extracellular space fraction (v_e), plasma perfusion (F_p), and the microvascular permeability surface area product. Our findings suggest that DCE‐CT is an appropriate reference for DCE‐MRI in bladder cancers as the only significant difference found between CT and MR parameter estimates were the no exchange limit estimates of v_p (P = 0.002). These results suggest that although water exchange between the intracellular and extravascular‐extracellular space has a negligible effect on DCE‐MRI, vascular–extravascular‐extracellular space water exchange may be more important. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

In vivo 3.0‐tesla magnetic resonance T1ρ and T2 relaxation mapping in subjects with intervertebral disc degeneration and clinical symptoms

The purpose of this study is (1) to determine the correlation between T_1ρ and T₂ and degenerative grade in intervertebral discs using in vivo 3.0‐T MRI, and (2) to determine the association between T_1ρ and T₂ and clinical findings as quantified by the SF‐36 Questionnaire and Oswestry Disability Index. Sixteen subjects participated in this study, and each completed SF‐36 and Oswestry Disability Index questionnaires. MRI T_1ρ and T₂ mapping was performed to determine T_1ρ (77 discs) and T₂ (44 discs) in the nucleus of the intervertebral disc, and T₂‐weighted images were acquired for Pfirrmann grading of disc degeneration. Pfirrmann grade was correlated with both T_1ρ (r = ?0.84; P < 0.01) and T₂ (r = ?0.61; P < 0.01). Mixed‐effects models demonstrate that only T_1ρ was associated with clinical questionnaires (R²_SF‐36 = 0.55, R²_O.D.I. = 0.56; P < 0.05). Although the averaged values of T_1ρ and T₂ were significantly correlated, they presented differences in spatial distribution and dynamic range, thus suggesting different sensitivities to tissue composition. This study suggests that T_1ρ may be sensitive to early degenerative changes (corroborating previous studies) and clinical symptoms in intervertebral disc degeneration. Magn Reson Med 63:1193–1200, 2010. © 2010 Wiley‐Liss, Inc.     

Contrast‐enhanced myocardial T1‐weighted scout (Look–Locker) imaging for the detection of myocardial damages in hypertrophic cardiomyopathy

Purpose

To assess the myocardial damage in hypertrophic cardiomyopathy (HCM) using contrast‐enhanced myocardial T1‐weighted scout (Look–Locker) magnetic resonance imaging (MRI).

Materials and Methods

Twenty‐three patients with HCM and seven comparative patients without known HCM serving as controls underwent cine, contrast‐enhanced myocardial T1‐weighted scout and delayed‐enhancement MRI using a 1.5T unit. Intervals of null points between myocardium and blood were compared among hyperenhancing and nullified myocardium of HCM and the normal myocardium. The relationship between these myocardial patterns and global cardiac functions was analyzed in HCM.

Results

The hyperenhancing myocardium, dense myocardial fibrosis in HCM had null points significantly shorter than blood, normal myocardium, and nullified myocardium of HCM (P < 0.0001). The number of hyperenhancing myocardial segments correlated with the ejection fraction (P = 0.045). The nullified myocardium of HCM showed shorter intervals of the null points between myocardium and blood than did the normal myocardium, indicating the dispersed myocardial fibrosis (P = 0.0032). The interval of null points between the nullified myocardium and blood showed a significant correlation with the increase in myocardial mass in HCM (P = 0.034).

Conclusion

Contrast‐enhanced myocardial T1‐weighted scout imaging has the potential for showing dispersed myocardial damage leading to increased myocardial mass in HCM, while the dense myocardial fibrosis correlated with reduced ejection fraction. J. Magn. Reson. Imaging 2009;30:778–784. © 2009 Wiley‐Liss, Inc.     

Usefulness of the application of the BLADE technique to reduce motion artifacts on navigation‐triggered prospective acquisition correction (PACE) T2‐weighted MRI (T2WI) of the liver

Purpose

To evaluate the effects of the application of the BLADE (Siemens, Siemens Medical Systems, Erlangen, Germany) technique, a technique to reduce motion artifacts, on navigator‐triggered prospective acquisition correction (PACE) T2‐weighted MRI (T2WI) of the liver.

Materials and Methods

Twenty‐three consecutive patients with a total of 57 localized hepatic diseases (39 malignant, 18 benign) and 57 patients without hepatic lesion underwent MR study during eupnea. The images were assessed quantitatively by calculating the liver–lesion contrast. Two subjective analyses were also performed. Two observers independently assessed the image quality and the confidence level of the detection and characterization of hepatic nodules using a five‐point scale. Statistical analysis was performed with the Wilcoxon matched‐pairs test except for the diagnostic performance evaluated with jackknife alternative free‐response receiver operating characteristic (JAFROC) analysis.

Results

There was no significant difference in the mean liver–lesion contrast between the PACE T2WI with BLADE (T2WI‐BLADE) (mean ± SD = 0.29 ± 0.14) and that without BLADE (0.30 ± 0.14) (P = 0.39). Visual assessment of PACE T2WI‐BLADE (4.8 ± 0.47) was superior to that without BLADE (4.3 ± 0.8) (P < 0.0001), although there were no significant differences in detecting and characterizing hepatic lesions using JAFROC analysis.

Conclusion

The BLADE technique could improve image quality by reducing motion artifacts on hepatic MRI without affecting the diagnostic performance. J. Magn. Reson. Imaging 2009;30:321–326. © 2009 Wiley‐Liss, Inc.     

Detection of hepatocellular carcinoma (HCC) using super paramagnetic iron oxide (SPIO)‐enhanced MRI: Added value of diffusion‐weighted imaging (DWI)

Purpose:

To evaluate whether diffusion‐weighted imaging (DWI) improves the detection of hepatocellular carcinoma (HCC) on super paramagnetic iron oxide (SPIO)‐enhanced MRI.

Materials and Methods:

This retrospective study group consisted of 30 patients with 50 HCC nodules who underwent MRI at 1.5 Tesla. Two combined MR sequence sets were compared for detecting HCC: SPIO‐enhanced MRI (axial T2‐weighted fast spin‐echo (FSE) and T1‐/T2*‐weighted fast field echo (FFE) scanned before and after administration of ferucarbotran) and SPIO‐enhanced MRI + DWI (SPIO‐enhanced MRI with axial DWI scanned before and after administration of ferucarbotran). Three blinded readers independently reviewed for the presence of HCC on a segment‐by‐segment basis using a four‐point confidence scale. The performance of the two combined MR sequence sets was evaluated using receiver operating characteristic (ROC) analysis.

Results:

The average area under the ROC curve (Az) of the three readers for the SPIO‐enhanced MRI + DWI set (0.870 ± 0.046) was significantly higher that that for the SPIO‐enhanced MRI set (0.820 ± 0.055) (P = .025). The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for detection of HCC were 66.0%, 98.0%, 90.0%, and 91.4%, respectively, for the SPIO‐enhanced MRI set, and 70.0%, 98.6%, 92.9%, and 92.4%, respectively, for the SPIO‐enhanced MRI + DWI set.

Conclusion:

The SPIO‐enhanced MRI + DWI set outperformed the SPIO‐enhanced MRI set for depicting HCC. J. Magn. Reson. Imaging 2010; 31: 373–382. © 2010 Wiley‐Liss, Inc.     

Bolus‐tracking MRI with a simultaneous T1‐ and T‐measurement

The aim of this study was to propose and evaluate a methodology to analyze simultaneously acquired T‐weighted dynamic susceptibility contrast (DSC) MRI and T₁‐weighted dynamic contrast enhanced (DCE) MRI data. Two generalized models of T‐relaxation are proposed to account for tracer leakage, and a two‐compartment exchange model is used to separate tracer in intra‐ and extravascular spaces. The methods are evaluated using data extracted from ROIs in three mice with subcutaneously implanted human colorectal tumors. Comparing plasma flow values obtained from DCE‐MRI and DSC‐MRI data defines a practical experimental paradigm to measure T‐relaxivities, and reveals a factor of 15 between values in tissue and blood. Comparing mean transit time values obtained from DCE‐MRI and DSC‐MRI without leakage correction, indicates a significant reduction of susceptibility weighting in DSC‐MRI during tracer leakage. A one‐parameter gradient correction model provides a good approximation for this susceptibility loss, but redundancy of the parameter limits the practical potential of this model for DSC‐MRI. Susceptibility loss is modeled more accurately with a variable T‐relaxivity, which allows to extract new parameters that cannot be derived from DSC‐MRI or DCE‐MRI alone. They reflect the cellular and vessel geometry, and thus may lead to a more complete characterization of tissue structure. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

In vivo diffusion tensor MRI of the human heart: Reproducibility of breath‐hold and navigator‐based approaches

The aim of this study was to implement a quantitative in vivo cardiac diffusion tensor imaging (DTI) technique that was robust, reproducible, and feasible to perform in patients with cardiovascular disease. A stimulated‐echo single‐shot echo‐planar imaging (EPI) sequence with zonal excitation and parallel imaging was implemented, together with a novel modification of the prospective navigator (NAV) technique combined with a biofeedback mechanism. Ten volunteers were scanned on two different days, each time with both multiple breath‐hold (MBH) and NAV multislice protocols. Fractional anisotropy (FA), mean diffusivity (MD), and helix angle (HA) fiber maps were created. Comparison of initial and repeat scans showed good reproducibility for both MBH and NAV techniques for FA (P > 0.22), MD (P > 0.15), and HA (P > 0.28). Comparison of MBH and NAV FA (FA_MBHday1 = 0.60 ± 0.04, FA_NAVday1 = 0.60 ± 0.03, P = 0.57) and MD (MD_MBHday1 = 0.8 ± 0.2 × 10^?3 mm²/s, MD_NAVday1 = 0.9 ± 0.2 × 10^?3 mm²/s, P = 0.07) values showed no significant differences, while HA values (HA_MBHday1Endo = 22 ± 10°, HA_{MBHday1Mid‐Endo} = 20 ± 6°, HA_{MBHday1Mid‐Epi} = ?1 ± 6°, HA_MBHday1Epi = ?17 ± 6°, HA_NAVday1Endo = 7 ± 7°, HA_{NAVday1Mid‐Endo} = 13 ± 8°, HA_{NAVday1Mid‐Epi} = ?2 ± 7°, HA_NAVday1Epi = ?14 ± 6°) were significantly different. The scan duration was 20% longer with the NAV approach. Currently, the MBH approach is the more robust in normal volunteers. While the NAV technique still requires resolution of some bulk motion sensitivity issues, these preliminary experiments show its potential for in vivo clinical cardiac diffusion tensor imaging and for delivering high‐resolution in vivo 3D DTI tractography of the heart. Magn Reson Med 70:454–465, 2013. © 2012 Wiley Periodicals, Inc.     

Comparison of dynamic contrast‐enhanced MRI and dynamic contrast‐enhanced CT biomarkers in bladder cancer

Dynamic contrast‐enhanced MRI (DCE‐MRI) is frequently used to provide response biomarkers in clinical trials of novel cancer therapeutics but assessment of their physiological accuracy is difficult. DCE‐CT provides an independent probe of similar pharmacokinetic processes and may be modeled in the same way as DCE‐MRI to provide purportedly equivalent physiological parameters. In this study, DCE‐MRI and DCE‐CT were directly compared in subjects with primary bladder cancer to assess the degree to which the model parameters report modeled physiology rather than artefacts of the measurement technique and to determine the interchangeability of the techniques in a clinical trial setting. The biomarker K^trans obtained by fitting an extended version of the Kety model voxelwise to both DCE‐MRI and DCE‐CT data was in excellent agreement (mean across subjects was 0.085 ± 0.030 min^?1 for DCE‐MRI and 0.087 ± 0.033 min^?1 for DCE‐CT, intermodality coefficient of variation 9%). The parameter v_p derived from DCE‐CT was significantly greater than that derived from DCE‐MRI (0.018 ± 0.006 compared to 0.009 ± 0.008, P = 0.0007) and v_e was in reasonable agreement only for low values. The study provides evidence that the biomarker K^trans is a robust parameter indicative of the underlying physiology and relatively independent of the method of measurement. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Prostate cancer vs. post‐biopsy hemorrhage: Diagnosis with T2‐ and diffusion‐weighted imaging

Purpose:

To assess the value of quantitative T2 signal intensity (SI) and apparent diffusion coefficient (ADC) to differentiate prostate cancer from post‐biopsy hemorrhage, using prostatectomy as the reference.

Materials and Methods:

Forty‐five men with prostate cancer underwent prostate magnetic resonance imaging (MRI), including axial T1‐weighted imaging (T1WI), T2WI, and single‐shot echo‐planar image (SS EPI) diffusion‐weighted imaging. Two observers measured, in consensus, normalized T2 signal intensity (SI) (nT2, relative to muscle T2 SI), ADC, and normalized ADC (nADC, relative to urine ADC) on peripheral zone (PZ) tumors, benign PZ hemorrhage, and non‐hemorrhagic benign PZ. Tumor maps from prostatectomy were used as the reference. Mixed model analysis of variance was performed to compare parameters among the three tissue classes, and Pearson's correlation coefficient was utilized to assess correlation between parameters and tumor size and Gleason score. Receiver‐operating characteristic (ROC)‐curve analysis was used to determine the performance of nT2, ADC, and nADC for diagnosis of prostate cancer.

Results:

nT2, ADC, and nADC were significantly lower in tumor compared with hemorrhagic and non‐hemorrhagic benign PZ (P < 0.0001). There was a weak but significant correlation between ADC and Gleason score (r = ?0.30, P = 0.0119), and between ADC and tumor size (r = ?0.40, P = 0.0027), whereas there was no correlation between nT2 and Gleason score and tumor size. The areas under the curve to distinguish tumor from benign hemorrhagic and non‐hemorrhagic PZ were 0.97, 0.96, and 0.933 for nT2, ADC, and nADC, respectively.

Conclusion:

Quantitative T2 SI and ADC/nADC values may be used to reliably distinguish prostate cancer from post‐biopsy hemorrhage. J. Magn. Reson. Imaging 2010;31:1387–1394. © 2010 Wiley‐Liss, Inc.

     

An MRI study of the differences in the rate of thrombolysis between red blood cell-rich and platelet-rich components of venous thrombi ex vivo

Purpose:

To test whether T₁‐weighted MRI can detect the differences in the rate of thrombolysis induced by recombinant tissue plasminogen activator (rt‐PA) between platelet‐rich regions and red blood cell (RBC)‐rich regions of venous thrombi ex vivo.

Materials and Methods:

Each of 21 venous thrombi ex vivo (8 pulmonary emboli and 13 in situ thrombi) was dissected along the longitudinal axis. Half of it was analyzed for the presence of platelet, fibrin, and RBC components by immunohistochemistry and the other half was imaged serially by high‐resolution T₁‐weighted three‐dimensional MRI to assess the progression of thrombolysis. The MR images were analyzed for proportions of the remaining platelet‐rich and RBC‐rich regions.

Results:

Laminated platelet‐rich regions, corresponding to Zahn lines, were confirmed immunohistochemically and by MRI in 18/21 venous thrombi. In T₁‐weighted MR images (TE/TR = 10/105 ms) the mean signal intensity of platelet‐rich regions was on average 2.3 higher than that of RBC‐rich regions. The rate of thrombolysis in platelet‐rich regions was on average 30% lower than in RBC‐rich regions. After 120 min of thrombolysis the proportion of lysed platelet‐rich regions was 0.27 ± 0.04 versus 0.40 ± 0.08 in RBC regions, which resulted in 1.4% decrease of lysed thrombus volume per 1% increase of platelet‐rich content.

Conclusion:

Venous thrombi are most often composed of interspersed platelet‐rich and RBC‐rich regions. T₁‐weighted MRI is capable of noninvasive discrimination between those two components of venous thrombi ex vivo which have a different susceptibility to thrombolysis by rt‐PA. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Features of the hypointense solid lesions in the female pelvis on T2‐weighted MRI

Most solid lesions in the female pelvis appearing hyperintense on T2‐weighted images should be interpreted as malignant. In contrast, if the solid lesions in the female pelvis appear hypointense on T2‐weighted images they may be benign. The characteristic imaging features of hyperintense solid lesions in the female pelvis on T2‐weighted images are well known, but various unusual causes and imaging features of hypointense solid lesions in the female pelvis on T2‐weighted images can be particularly misleading. Therefore, careful assessment of hypointense solid lesions in the female pelvis on T2‐weighted images is warranted. In this article, we demonstrate a variety of hypointense solid lesions in the female pelvis on T2‐weighted images. Familiarity with the clinical setting and imaging features of hypointense solid lesions in the female pelvis on T2‐weighted images will facilitate prompt, accurate diagnosis and treatment. J. Magn. Reson. Imaging 2014;39:493–503 . © 2014 Wiley Periodicals, Inc .