In vivo MRI of altered proton signal intensity and T2 relaxation in a bleomycin model of pulmonary inflammation and fibrosis

Purpose:

To investigate the ability of proton (¹H) magnetic resonance imaging (MRI) to distinguish between pulmonary inflammation and fibrosis.

Materials and Methods:

Three groups of Sprague‐Dawley rats (n = 5) were instilled intratracheally with bleomycin (2.5 U/kg or 3.5 U/kg) in saline or with saline only. Rats were imaged at 2.0 Tesla using a multi‐slice Carr‐Purcell‐Meilboom‐Gill (CPMG) sequence with 6 ms echo spacing. Signal intensity (S₀) and T₂ were calculated on a pixel‐by‐pixel basis using images collected before dosing and 1, 2, 4, and 7 weeks after. At each time point, data from dosed animals were compared with controls, and bivariate statistical analysis was used to classify image pixels containing abnormal tissue. At week 7, pulmonary function tests were performed, then all rats were killed, left lungs were formalin fixed and tri‐chrome stained for histological analysis of collagen content, and right lungs were used to measure water and hydroxyproline (collagen) content.

Results:

The product S₀×T₂ significantly correlated with water and collagen content in the high‐dose group (P = 0.004 and P = 0.03, respectively). However, S₀ and T₂ of abnormal tissue were correlated for all time points (r = 0.93, P < 0.001), and could not distinguish inflammation from fibrosis.

Conclusion:

MRI can be used to confidently localize pulmonary inflammation and fibrosis, but it lacks specificity. J. Magn. Reson. Imaging 2010;31:1091–1099. © 2010 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.

     

High-resolution MRI of excised human prostate specimens acquired with 9.4T in detection and identification of cancers: validation of a technique

Purpose:

To evaluate feasibility of high‐resolution, high‐field ex vivo prostate magnetic resonance imaging (MRI) as an aid to guide pathologists' examination and develop in vivo MRI methods.

Materials and Methods:

Unfixed excised prostatectomy specimens (n = 9) were obtained and imaged immediately after radical prostatectomy under an Institutional Review Board‐approved protocol. High‐resolution T2‐weighted (T2W) MRI of specimens were acquired with a Bruker 9.4 T scanner to correlate with whole‐mount histology. Additionally, T2 and apparent diffusion coefficient (ADC) maps were generated.

Results:

By visual inspection of the nine prostate specimens imaged, high‐resolution T2W MRI showed improved anatomical detail compared to published low‐resolution images acquired at 4 T as published by other investigators. Benign prostatic hyperplasia, adenocarcinomas, curvilinear duct architecture distortion due to adenocarcinomas, and normal radial duct distribution were readily identified. T2 was ≈10 msec longer (P < 0.03) and the ADC was ≈1.4 times larger (P < 0.002) in the normal peripheral zone compared to the peripheral zone with prostate cancer.

Conclusion:

Differences in T2 and ADC between benign and malignant tissue are consistent with in vivo data. High‐resolution, high‐field MRI has the potential to improve the detection and identification of prostate structures. The protocols and techniques developed in this study could augment routine pathological analysis of surgical specimens and guide treatment of prostate cancer patients. J. Magn. Reson. Imaging 2011. © 2011 Wiley‐Liss, Inc.     

Effect of disease progression on liver apparent diffusion coefficient and T2 values in a murine model of hepatic fibrosis at 11.7 Tesla MRI

Purpose:

To evaluate the effects of hepatic fibrosis on ADC and T₂ values of ex vivo murine liver specimens imaged using 11.7 Tesla (T) MRI.

Materials and Methods:

This animal study was IACUC approved. Seventeen male, C57BL/6 mice were divided into control (n = 2) and experimental groups (n = 15), the latter fed a 3, 5‐dicarbethoxy‐1, 4‐dihydrocollidine (DDC) supplemented diet, inducing hepatic fibrosis. Ex vivo liver specimens were imaged using an 11.7T MRI scanner. Spin‐echo pulsed field gradient and multi‐echo spin‐echo acquisitions were used to generate parametric ADC and T₂ maps, respectively. Degrees of fibrosis were determined by the evaluation of a pathologist as well as digital image analysis. Scatterplot graphs comparing ADC and T₂ to degrees of fibrosis were generated and correlation coefficients were calculated.

Results:

Strong correlation was found between degrees of hepatic fibrosis and ADC with higher degrees of fibrosis associated with lower hepatic ADC values. Moderate correlation between hepatic fibrosis and T₂ values was seen with higher degrees of fibrosis associated with lower T₂ values.

Conclusion:

Inverse relationships between degrees of fibrosis and both ADC and T₂ are seen, highlighting the utility of these parameters in the ongoing development of an MRI methodology to quantify hepatic fibrosis. J. Magn. Reson. Imaging 2012;35:140‐146. © 2011 Wiley Periodicals, Inc.     

Diffusion-weighted and dynamic contrast-enhanced MRI in evaluation of early treatment effects during neoadjuvant chemotherapy in breast cancer patients

Purpose:

To use dynamic contrast‐enhanced (DCE) and diffusion‐weighted (DW) MRI at 3 Tesla (T) for early evaluation of treatment effects in breast cancer patients undergoing neoadjuvant chemotherapy (NAC), and assess the reliability of DW‐MRI.

Materials and Methods:

DW‐ and DCE‐MRI acquisitions of 15 breast cancer patients were performed before and after one cycle of NAC. MRI tumor diameter and volume, apparent diffusion coefficient (ADC) and kinetic parameters (K^trans, v_e) were derived. The reliability of ADC before NAC was assessed. Changes in MRI parameters after NAC were analyzed, and logistic regression analysis was used to find the best predictors for pathologic response.

Results:

The reliability for ADC values was high, with intraclass correlation coefficient of 0.84 (P = 0.001). After one cycle of NAC, MRI tumor diameter (8%, P = 0.005) and tumor volume (30%, P = 0.008) was reduced for all patients, while ADC mean values increased (0.12 mm²/s, P = 0.008). The best predictor for treatment response was a change in MRI tumor diameter with mean error rate of 0.167 (13% for responders, 5% for nonresponders, P = 0.291).

Conclusion:

Changes in MRI derived tumor diameter and ADC after only one cycle of NAC could provide a valuable tool for early evaluation of treatment effects in breast cancer patients. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Prediction of locally recurrent prostate cancer after radiation therapy: Incremental value of 3T diffusion‐weighted MRI

Purpose

To prospectively evaluate the incremental value of diffusion‐weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps in addition to T2‐weighted imaging (T2WI) for predicting locally recurrent prostate cancer in patients with biochemical failure after radiation therapy.

Materials and Methods

Thirty‐six consecutive patients with an increased prostate‐specific antigen level after radiation therapy underwent 3T MRI followed by transrectal biopsy. The MRI findings and biopsy results were correlated in sextant prostate sectors of peripheral zones (PZs). Two radiologists in consensus reviewed T2WI and combined T2WI and DWI with ADC maps, and rated the likelihood of recurrent cancer on a five‐point scale. ADC values were calculated for recurrent cancer and benign tissue.

Results

Of 216 sectors, 65 prostate sectors (30%) were positive for cancer in 18 patients. For predicting recurrent cancer, combined T2WI and DWI showed a greater sensitivity compared to T2WI (P < 0.001). A significantly greater area under the receiver operating characteristics curve (Az) was determined for combined T2WI and DWI (Az = 0.879, P < 0.01) as compared to T2WI (Az = 0.612). Mean ADC values between recurrent cancer and benign tissue showed a statistically significant difference (P < 0.01).

Conclusion

For predicting locally recurrent prostate cancer after radiation therapy, the use of combined T2WI and DWI showed a better diagnostic performance compared to T2WI. J. Magn. Reson. Imaging 2009;29:391–397. © 2009 Wiley‐Liss, Inc.     

Metabolic alterations: A biomarker for radiation‐induced normal brain injury—an MR spectroscopy study

Purpose

To assess if interval changes in metabolic status in normal cerebral tissue after radiation therapy (RT) can be detected by 2D CSI (chemical shift imaging) proton spectroscopy.

Materials and Methods

Eleven patients with primary brain tumors undergoing cranial radiation therapy (RT) were included. 2D‐CSI MRS was performed before, during, and after the course of RT with the following parameters: TE/TR 144/1500 ms, field of view (FOV) 24, thickness 10 mm, matrix 16 × 16. The metabolic ratios choline/creatine (Cho/Cr), N‐acetylaspartate (NAA)/Cr, and NAA/Cho in normal brain tissue were calculated.

Results

NAA/Cr and Cho/Cr were significantly decreased at week 3 during RT and at 1 month and 6 months after RT compared to values prior to RT (P < 0.01). The NAA/Cr ratio decreased by ?0.19 ± 0.05 (mean ± standard error [SE]) at week 3 of RT, ?0.14 ± 0.06 at the last week of RT, ?0.14 ± 0.05 at 1 month after RT, and ?0.30 ± 0.08 at 6 months after RT compared to the pre‐RT value of 1.43 ± 0.04. The Cho/Cr ratio decreased by ?0.27 ± 0.05 at week 3 of RT, ?0.11 ± 0.05 at the last week of RT, ?0.26 ± 0.05 at 1 month after RT and ?0.25 ± 0.07 at 6 months after RT from the pre‐RT value of 1.29 ± 0.03. Changes in Cho/Cr were correlated with the interaction of the radiation dose and dose‐volume at week 3 of RT, during the last week of RT (P < 0.005), and at 1 month after RT (P = 0.017).

Conclusion

The results of this study suggest that MRS can detect early metabolic changes in normal irradiated brain tissue. J. Magn. Reson. Imaging 2009;29:291–297. © 2009 Wiley‐Liss, Inc.

     

Reproducibility and correlation between quantitative and semiquantitative dynamic and intrinsic susceptibility‐weighted MRI parameters in the benign and malignant human prostate

Purpose:

To assess the reproducibility of relaxivity‐ and susceptibility‐based dynamic contrast‐enhanced magnetic resonance imaging (MRI) in the benign and malignant prostate gland and to correlate the kinetic parameters obtained.

Materials and Methods:

Twenty patients with prostate cancer underwent paired scans before and after androgen deprivation therapy. Quantitative parametric maps for T₁‐ and T₂*‐weighted parameters were calculated (K^trans, k_ep,v_e, IAUC₆₀, rBV, rBF, and R₂*). The reproducibility of and correlation between each parameter were determined using standard methods at both timepoints.

Results:

T₁‐derived parameters are more reproducible than T₂*‐weighted measures, both becoming more variable following androgen deprivation (variance coefficients for prostate K^trans and rBF increased from 13.9%–15.8% and 42.5%–90.8%, respectively). Tumor R₂* reproducibility improved after androgen ablation (23.3%–11.8%). IAUC₆₀ correlated strongly with K^trans, v_e, and k_ep (all P < 0.001). R₂* did not correlate with other parameters.

Conclusion:

This study is the first to document the variability and repeatability of T₁‐ and T₂*‐weighted dynamic MRI and intrinsic susceptibility‐weighted MRI for the various regions of the human prostate gland before and after androgen deprivation. These data provide a valuable source of reference for groups that plan to use dynamic contrast‐enhanced MRI or intrinsic susceptibility‐weighted MRI for the assessment of treatment response in the benign or malignant prostate. J. Magn. Reson. Imaging 2010;32:155–164. © 2010 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.     

Shorter difference between myocardium and blood optimal inversion time suggests diffuse fibrosis in dilated cardiomyopathy

Purpose:

To find evidence of diffuse fibrosis in dilated cardiomyopathy (DCM) patients by comparing measurements on clinical late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) studies between DCM and healthy subjects.

Materials and Methods:

LGE‐CMR and the Look–Locker images from 20 DCM patients and 17 healthy controls were analyzed. Blood signal‐to‐noise ratio (SNR), myocardium SNR, and blood‐to‐myocardium contrast‐to‐noise ratio (CNR) were measured on the LGE‐CMR images. The optimal inversion time (TI) to null blood and myocardium was determined on the Look–Locker images. The postcontrast T₁ was estimated using a phantom study that correlated optimal TI and heart rate to T₁.

Results:

The blood SNR was lower, myocardium SNR was higher, and the blood‐to‐myocardium CNR was lower (6.6 ± 0.7 vs. 10.3 ± 0.9, P = 0.004) on DCM LGE‐CMR images as compared to controls. The blood‐myocardium optimal TI difference (ΔTI) was lower (38 ± 2 msec vs. 55 ± 3 msec, P < 0.001) in DCM, and the estimated blood‐myocardium T₁ difference (ΔT₁) (116 ± 6 msec vs. 152 ± 8 msec, P = 0.001) was also lower.

Conclusion:

DCM patients have reduced blood‐myocardium ΔTI and ΔT₁, and lower CNR as compared to controls, suggesting the presence of diffuse fibrosis. This may impact the interpretation of LGE data. J. Magn. Reson. Imaging 2009;30:967–972. © 2009 Wiley‐Liss, Inc.     

Diffusion‐weighted imaging of prostate cancer: Correlation between apparent diffusion coefficient values and tumor proliferation

Purpose

To investigate whether the apparent diffusion coefficient (ADC) values of prostate cancer (PCa) are able to reflect tumor proliferation.

Materials and Methods

The clinical and pathological information for 38 patients with PCa and 33 patients with benign prostate hyperplasia (BPH) were studied. Examination of the patients was performed using a 1.5 T superconducting magnetic scanner equipped with a pelvic phased‐array multicoil. Diffusion‐weighted images (DWIs) were acquired using an echo‐planar imaging sequence. The ADC values of PCa, BPH, and peripheral zone (PZ) were calculated. The cellularity of PCa was recorded based on hematoxylin and eosin staining. The proliferating cell nuclear antigen (PCNA) was detected using an immunohistochemical technique.

Results

The ADC values of PCa, BPH, and PZ were 49.32 ± 12.68 × 10^?5 mm²/s, 86.73 ± 26.75 × 10^?5 mm²/s, and 126.25 ± 27.21 × 10^?5 mm²/s, respectively. The ADC values of PCa were lower than those of BPH and PZ (P < 0.05). The cellularity and PCNA labeling index (LI) of PCa were higher than those of BPH (P < 0.05). The ADC values of PCa were negatively correlated with those of cellularity and PCNA LI (r = ?0.646 and ?0.446, respectively; P < 0.05).

Conclusion

The ADC values of PCa can reveal the differences in proliferative activity between PCa and BPH. These values are therefore able to predict the proliferative rate of variously differentiated prostate cancers. J. Magn. Reson. Imaging 2009;29:1360–1366. © 2009 Wiley‐Liss, Inc.

     

Reducing the influence of b-value selection on diffusion-weighted imaging of the prostate: evaluation of a revised monoexponential model within a clinical setting

Purpose:

To compare the accuracy of standard and revised monoexponential models of diffusion‐weighted magnetic resonance imaging (DW‐MRI) data for differentiating malignant from benign prostate tissue, using surgical pathology as the reference standard.

Materials and Methods:

The Institutional Review Board waived informed consent for this Health Insurance Portability and Accountability Act (HIPAA)‐compliant, retrospective study of 46 patients (median age = 61 years; range: 42–85 years) who underwent DW‐MRI between May and December 2008 before radical prostatectomy for biopsy‐proven prostate cancer, had no prior treatment, and had whole‐mount step‐section pathology maps available showing at least one peripheral zone (PZ) lesion >0.1 cm³. DW‐MRI data were obtained for b‐values of 0, 400, and 700 s/mm². Apparent diffusion coefficients (ADCs) were estimated from PZ regions of interest (ROIs) on b = 0, 700 and b = 0, 400 s/mm² images, using a standard monoexponential model. The true diffusion coefficient (D) and perfusion fraction (f) were measured using a revised monoexponential model incorporating all three b‐values. Areas under receiver operating characteristic curves (AUCs) were calculated to assess the accuracy of individual parameters and a logistic regression model combining D and f (D+f) in distinguishing malignant ROIs; P < 0.05 denoted significance.

Results:

ADC₄₀₀ (AUC = 0.81, P < 0.0001), ADC₇₀₀ (AUC = 0.79, P < 0.0001), D (AUC = 0.71, P = 0.0001) and D + f distinguished malignant from benign ROIs (AUC = 0.82, P < 0.0001), but f did not (AUC = 0.56, P = 0.28); D + f was significantly more accurate than D (P = 0.016) but not more accurate than ADC₄₀₀ (P = 0.26) or ADC₇₀₀ (P = 0.12).

Conclusion:

The true diffusion coefficient provides an additional DW‐MRI parameter for distinguishing prostate cancer that is less influenced than the ADC by b‐value selection. J. Magn. Reson. Imaging 2011;35:660‐668. © 2011 Wiley Periodicals, Inc.     

Diffusion‐weighted MRI for monitoring tumor response to photodynamic therapy

Purpose:

To examine diffusion‐weighted MRI (DW‐MRI) for assessing the early tumor response to photodynamic therapy (PDT).

Materials and Methods:

Subcutaneous tumor xenografts of human prostate cancer cells (CWR22) were initiated in athymic nude mice. A second‐generation photosensitizer, Pc 4, was delivered to each animal by a tail vein injection 48 h before laser illumination. A dedicated high‐field (9.4 Tesla) small animal MR scanner was used to acquire diffusion‐weighted MR images pre‐PDT and 24 h after the treatment. DW‐MRI and apparent diffusion coefficients (ADC) were analyzed for 24 treated and 5 control mice with photosensitizer only or laser light only. Tumor size, prostate specific antigen (PSA) level, and tumor histology were obtained at different time points to examine the treatment effect.

Results:

Treated mice showed significant tumor size shrinkage and decrease of PSA level within 7 days after the treatment. The average ADC of the 24 treated tumors increased 24 h after PDT (P < 0.001) comparing with pre‐PDT. The average ADC was 0.511 ± 0.119 × 10^?3 mm²/s pre‐PDT and 0.754 ± 0.181 × 10^?3 mm²/s 24 h after the PDT. There is no significant difference in ADC values pre‐PDT and 24 h after PDT in the control tumors (P = 0.20).

Conclusion:

The change of tumor ADC values measured by DW‐MRI may provide a noninvasive imaging marker for monitoring tumor response to Pc 4‐PDT as early as 24 h. J. Magn. Reson. Imaging 2010;32:409–417. © 2010 Wiley‐Liss, Inc.

     

Clinical utility of apparent diffusion coefficient (ADC) values in patients with prostate cancer: Can ADC values contribute to assess the aggressiveness of prostate cancer?

Purpose

To retrospectively evaluate the relationship between apparent diffusion coefficient (ADC) values and Gleason score (GS) in prostate cancer.

Methods

A total of 60 patients who underwent radical prostatectomy for clinically localized prostate cancer were selected for this study. Diffusion‐weighted magnetic resonance (MR) images were obtained using a 1.5 T system. ADC values were analyzed between three groups: GS of 6 or less (n = 7); GS of 7 (n = 37); and GS of 8 or higher (n = 16). ADC values of the three GS groups were statistically analyzed in order to determine the relationship with GS. In the 37 patients with GS = 7 the difference in ADC values between GS 3+4 and GS 4+3 was analyzed.

Results

Median ADC values (10^?3 mm²/s) of the three GS groups were 1.04 (GS = 6 or less), 0.867 (GS = 7), and 0.729 (GS = 8 or higher). Although there was considerable overlap among the groups, the differences in ADC were statistically significant (P < 0.0001). There was a significant inverse correlation between GS and ADC values (z = ?0.437, P < 0.0005). Median ADC values (10^?3 mm²/s) of GS 3+4 and GS 4+3 patients were 0.88 and 0.814, respectively (P < 0.05).

Conclusion

ADC values showed a negative correlation with GS. Pathologically, however, there was considerable intrasubject heterogeneity. J. Magn. Reson. Imaging 2011;33:167–172. © 2010 Wiley‐Liss, Inc.

     

Inhomogeneous sodium accumulation in the ischemic core in rat focal cerebral ischemia by 23Na MRI

Purpose

To test the hypotheses that (i) the regional heterogeneity of brain sodium concentration ([Na⁺]_br) provides a parameter for ischemic progression not available from apparent diffusion coefficient (ADC) data, and (ii) [Na⁺]_br increases more in ischemic cortex than in the caudate putamen (CP) with its lesser collateral circulation after middle cerebral artery occlusion in the rat.

Materials and Methods

²³Na twisted projection MRI was performed at 3 Tesla. [Na⁺]_br was independently determined by flame photometry. The ischemic core was localized by ADC, by microtubule‐associated protein‐2 immunohistochemistry, and by changes in surface reflectivity.

Results

Within the ischemic core, the ADC ratio relative to the contralateral tissue was homogeneous (0.63 ± 0.07), whereas the rate of [Na⁺]_br increase (slope) was heterogeneous (P < 0.005): 22 ± 4%/h in the sites of maximum slope versus 14 ± 1%/h elsewhere (here 100% is [Na⁺]_br in the contralateral brain). Maximum slopes in the cortex were higher than in CP (P < 0.05). In the ischemic regions, there was no slope/ADC correlation between animals and within the same brain (P > 0.1). Maximum slope was located at the periphery of ischemic core in 8/10 animals.

Conclusion

Unlike ADC, ²³Na MRI detected within‐core ischemic lesion heterogeneity. J. Magn. Reson. Imaging 2009;30:18–24. © 2009 Wiley‐Liss, Inc.     

T(1ρ) and T(2) quantitative magnetic resonance imaging analysis of cartilage regeneration following microfracture and mosaicplasty cartilage resurfacing procedures

Purpose

To examine T_1ρ (T1rho) and T₂ quantitative magnetic resonance imaging (MRI) in evaluating cartilage regeneration following microfracture (MFx) and mosaicplasty (MOS) cartilage resurfacing procedures.

Materials and Methods

Eighteen patients underwent MFx and eight patients underwent MOS to treat symptomatic focal cartilage defects. Quantitative T_1ρ and T₂ maps were acquired at 3–6 months and 1 year after surgery. The area of resurfacing was identified, and T_1ρ and T₂ values for the regenerated tissue (RT) and normal cartilage (NC) were acquired. RT/NC ratios were calculated to standardize absolute T_1ρ and T₂ values. Data were prospective, cross‐sectional, and nonrandomized.

Results

T_1ρ and T₂ showed good reanalysis reproducibility for RT and NC. Significant differences between RT and NC were present following MFx at 3–6 months for T_1ρ and T₂ values as well as following MOS at 3–6 months and 1 year for T_1ρ values. Following MFx, the T₂ RT/NC ratio was significantly different between 3–6 months and 1 year (P = 0.02), while the T_1ρ RT/NC ratio approached significance (P = 0.07). Following MOS, the T_1ρ and T₂ RT/NC ratios were not significantly different between the two timepoints.

Conclusion

T_1ρ and T₂ MRI are complementary and reproducible methods for quantitatively and noninvasively monitoring regeneration of RT following MFx and MOS. J. Magn. Reson. Imaging 2010;32:914–923. © 2010 Wiley‐Liss, Inc.     

3D flow‐independent peripheral vessel wall imaging using T2‐prepared phase‐sensitive inversion‐recovery steady‐state free precession

Purpose:

To develop a 3D flow‐independent peripheral vessel wall imaging method using T₂‐prepared phase‐sensitive inversion‐recovery (T₂PSIR) steady‐state free precession (SSFP).

Materials and Methods:

A 3D T₂‐prepared and nonselective inversion‐recovery SSFP sequence was designed to achieve flow‐independent blood suppression for vessel wall imaging based on T₁ and T₂ properties of the vessel wall and blood. To maximize image contrast and reduce its dependence on the inversion time (TI), phase‐sensitive reconstruction was used to restore the true signal difference between vessel wall and blood. The feasibility of this technique for peripheral artery wall imaging was tested in 13 healthy subjects. Image signal‐to‐noise ratio (SNR), wall/lumen contrast‐to‐noise ratio (CNR), and scan efficiency were compared between this technique and conventional 2D double inversion recovery – turbo spin echo (DIR‐TSE) in eight subjects.

Results:

3D T₂PSIR SSFP provided more efficient data acquisition (32 slices and 64 mm in 4 minutes, 7.5 seconds per slice) than 2D DIR‐TSE (2–3 minutes per slice). SNR of the vessel wall and CNR between vessel wall and lumen were significantly increased as compared to those of DIR‐TSE (P < 0.001). Vessel wall and lumen areas of the two techniques are strongly correlated (intraclass correlation coefficients: 0.975 and 0.937, respectively; P < 0.001 for both). The lumen area of T₂PSIR SSFP is slightly larger than that of DIR‐TSE (P = 0.008). The difference in vessel wall area between the two techniques is not statistically significant.

Conclusion:

T₂PSIR SSFP is a promising technique for peripheral vessel wall imaging. It provides excellent blood signal suppression and vessel wall/lumen contrast. It can cover a 3D volume efficiently and is flow‐ and TI‐independent. J. Magn. Reson. Imaging 2010;32:399–408. © 2010 Wiley‐Liss, Inc.     

Early (72-hour) detection of radiotherapy-induced changes in an experimental tumor model using diffusion-weighted imaging, diffusion tensor imaging, and Q-space imaging parameters: a comparative study

Purpose:

To assess and compare the potential of various diffusion‐related magnetic resonance imaging (MRI) parameters to detect early radiotherapy (RT)‐induced changes in tumors.

Materials and Methods:

Nineteen tumors in a rat model were imaged on a clinical 3T system before and 72 hours after a single RT session. Diffusion imaging was performed using an echo planar sequence containing 16 b‐factors and six gradient directions. This allowed us to perform a tensor analysis of mono‐ and biexponential decays and a q‐space analysis. Parametric maps (both trace and fractional anisotropy) were reconstructed for: 2‐point apparent diffusion coefficient (ADC), 16‐point ADC, biexponential amplitudes and ADCs, and height, width, and kurtosis of the probability density function (PDF). A texture analysis yielded quantities such as average and contrast. The sensitivity of diffusion‐related parameters was quantified in terms of the mean relative difference (when comparing pre‐ and post‐RT status).

Results:

Traces and anisotropies display differences in response to RT. Average traces are most sensitive for ADCs and kurtosis. Average anisotropies are all very sensitive except the slow biexponential component. The best contrast (traces) was found for the ADCs and the width of the PDF.

Conclusion:

ADC performed well, but high b‐values analysis added extra sensitive parameters for monitoring early RT‐induced changes. J. Magn. Reson. Imaging 2012;409‐417. © 2011 Wiley Periodicals, Inc.     

Comparison of diffusion-weighted MRI and MR volumetry in the evaluation of early treatment outcomes after preoperative chemoradiotherapy for locally advanced rectal cancer

Purpose:

To compare diffusion‐weighted imaging (DWI) and magnetic resonance (MR) volumetry for predicting treatment outcomes of locally advanced rectal cancers with preoperative chemoradiotherapy (CRT).

Materials and Methods:

This prospective study was approved by our Institutional Review Board. Thirty‐four patients underwent three MR examinations: pre‐CRT (before CRT), early CRT (2 weeks after CRT initiation), and post‐CRT (before surgery). The tumor apparent diffusion coefficient (ADC), ADC increase rate, and volume reduction rate were compared between responders and nonresponders using three reference standards: downstaging, modified Response Evaluation Criteria in Solid Tumors (mRECIST), and tumor regression grade (TRG). For DWI and volumetry, differences between responders and nonresponders were assessed by receiver operating characteristic analysis.

Results:

The median early tumor volume reduction rate of responders, subgrouped by downstaging and mRECIST (47.97% and 53.97%, respectively), was significantly higher than that of nonresponders (20.94% and 20.36%; P = 0.0024 and 0.0001, respectively), but there were no significant differences in pre‐CRT ADC and early ADC increase rate using all references. When using the downstaging and mRECIST, the diagnostic performance of early tumor volume reduction rate (Az = 0.81 and 0.94, respectively) was higher than that of pre‐CRT ADC (Az = 0.55 and 0.62; P = 0.033 and 0.007) and early ADC increase rate (Az = 0.58 and 0.64; P = 0.055 and 0.01) for predicting the treatment outcome. For TRG, there were no significant differences between DWI and volumetry.

Conclusion:

Early tumor volume reduction rate at the second week after CRT initiation may be a better indicator than DWI based on the mean ADC measurements for predicting CRT treatment outcome. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

T(2) -weighted STIR imaging of myocardial edema associated with ischemia-reperfusion injury: the influence of proton density effect on image contrast

Purpose

To investigate the contribution of proton density (PD) in T₂‐STIR based edema imaging in the setting of acute myocardial infarction (AMI).

Materials and Methods

Canines (n = 5), subjected to full occlusion of the left anterior descending artery for 3 hours, underwent serial magnetic resonance imaging (MRI) studies 2 hours postreperfusion (day 0) and on day 2. During each study, T₁ and T₂ maps, STIR (TE = 7.1 msec and 64 msec) and late gadolinium enhancement (LGE) images were acquired. Using T₁ and T₂ maps, relaxation and PD contributions to myocardial edema contrast (EC) in STIR images at both TEs were calculated.

Results

Edematous territories showed significant increase in PD (20.3 ± 14.3%, P < 0.05) relative to healthy territories. The contributions of T₁ changes and T₂ or PD changes toward EC were in opposite directions. One‐tailed t‐test confirmed that the mean T₂ and PD‐based EC at both TEs were greater than zero. EC from STIR images at TE = 7.1 msec was dominated by PD than T₂ effects (94.3 ± 11.3% vs. 17.6 ± 2.5%, P < 0.05), while at TE = 64 msec, T₂ effects were significantly greater than PD effects (90.8 ± 20.3% vs. 12.5 ± 11.9%, P < 0.05). The contribution from PD in standard STIR acquisitions (TE = 64 msec) was significantly higher than 0 (P < 0.05).

Conclusion

In addition to T₂‐weighting, edema detection in the setting of AMI with T₂‐weighted STIR imaging has a substantial contribution from PD changes, likely stemming from increased free‐water content within the affected tissue. This suggests that imaging approaches that take advantage of both PD as well as T₂ effects may provide the optimal sensitivity for detecting myocardial edema. J. Magn. Reson. Imaging 2011;33:962–967. © 2011 Wiley‐Liss, Inc.