Diagnosis of cirrhosis with intravoxel incoherent motion diffusion MRI and dynamic contrast‐enhanced MRI alone and in combination: Preliminary experience

Purpose:

To report our preliminary experience with the use of intravoxel incoherent motion (IVIM) diffusion‐weighted magnetic resonance imaging (DW‐MRI) and dynamic contrast‐enhanced (DCE)‐MRI alone and in combination for the diagnosis of liver cirrhosis.

Materials and Methods:

Thirty subjects (16 with noncirrhotic liver, 14 with cirrhosis) were prospectively assessed with IVIM DW‐MRI (n = 27) and DCE‐MRI (n = 20). IVIM parameters included perfusion fraction (PF), pseudodiffusion coefficient (D*), true diffusion coefficient (D), and apparent diffusion coefficient (ADC). Model‐free DCE‐MR parameters included time to peak (TTP), upslope, and initial area under the curve at 60 seconds (IAUC60). A dual input single compartmental perfusion model yielded arterial flow (Fa), portal venous flow (Fp), arterial fraction (ART), mean transit time (MTT), and distribution volume (DV). The diagnostic performances for diagnosis of cirrhosis were evaluated for each modality alone and in combination using logistic regression and receiver operating characteristic analyses. IVIM and DCE‐MR parameters were compared using a generalized estimating equations model.

Results:

PF, D*, D, and ADC values were significantly lower in cirrhosis (P = 0.0056–0.0377), whereas TTP, DV, and MTT were significantly increased in cirrhosis (P = 0.0006–0.0154). There was no correlation between IVIM‐ and DCE‐MRI parameters. The highest Az (areas under the curves) values were observed for ADC (0.808) and TTP‐DV (0.952 for each). The combination of ADC with DV and TTP provided 84.6% sensitivity and 100% specificity for diagnosis of cirrhosis.

Conclusion:

The combination of DW‐MRI and DCE‐MRI provides an accurate diagnosis of cirrhosis. J. Magn. Reson. Imaging 2010;31:589–600. © 2010 Wiley‐Liss, Inc.     

Head and neck tumours: combined MRI assessment based on IVIM and TIC analyses for the differentiation of tumors of different histological types

Objectives

We evaluated the combined use of intravoxel incoherent motion (IVIM) and time-signal intensity curve (TIC) analyses to diagnose head and neck tumours.

Methods

We compared perfusion-related parameters (PP) and molecular diffusion values (D) determined from IVIM theory and TIC profiles among 92 tumours with different histologies.

Results

IVIM parameters (f and D values) and TIC profiles in combination were distinct among the different types of head and neck tumours, including squamous cell carcinomas (SCCs), lymphomas, malignant salivary gland tumours, Warthin’s tumours, pleomorphic adenomas and schwannomas. A multiparametric approach using both IVIM parameters and TIC profiles differentiated between benign and malignant tumours with 97 % accuracy and diagnosed different tumour types with 89 % accuracy.

Conclusions

Combined use of IVIM parameters and TIC profiles has high efficacy in diagnosing head and neck tumours.

Key points

? Head and neck tumours have wide MR perfusion/diffusion properties. ? Dynamic contrast-enhanced (DCE) MR imaging can characterise tumour perfusion (TIC analysis). ? Intravoxel incoherent motion (IVIM) imaging can provide diffusion and perfusion properties. ? However, IVIM or DCE imaging alone is insufficient for diagnosing head/neck tumours. ? Multiparametric approach using both IVIM and TIC profiles can facilitate the diagnosis.     

Impact of outliers on diffusion tensor and Q-ball imaging: clinical implications and correction strategies

Purpose:

To measure the impact of corrupted images often found to occur in diffusion‐weighted magnetic resonance imaging (DW‐MRI). To propose a robust method for the correction of outliers, applicable to diffusion tensor imaging (DTI) and q‐ball imaging (QBI).

Materials and Methods:

Monte Carlo simulations were carried out to measure the impact of outliers on DTI and QBI reconstruction in a single voxel. Methods to correct outliers based on q‐space interpolation and direction removal were then implemented and validated in real image data.

Results:

Corruption in a single voxel led to clear variations in DTI and QBI metrics. In real data, the method of q‐space interpolation was successful in identifying corrupted voxels and restoring them to values consistent with those of uncorrupted images.

Conclusion:

For images containing few gradient directions, where outlier removal was either impossible due to limited volumes or resulted in large changes in DTI/QBI metrics, q‐space interpolation proved to be the method of choice for image restoration. A simple decision support system is proposed to assist clinicians in the correction of their corrupted DW data. J. Magn. Reson. Imaging 2011;33:1491–1502. © 2011 Wiley‐Liss, Inc.     

Chemical shift imaging in the head and neck at 3T: initial results

Purpose

To determine the optimal method to correct air and tissue susceptibility differences in the head and neck to allow proton (¹H) chemical shift imaging (CSI) to be performed at 3T.

Materials and Methods

Shimming protocols (iterative, first‐order, and second‐order) and perfluorocarbon (PFC) pads were evaluated using water peak linewidth measurements obtained from single‐voxel magnetic resonance spectroscopy (MRS) on a head and neck phantom. After optimization of the technique, CSI was then tested on 14 patients with head and neck tumors.

Results

Second‐order shimming (water peak linewidth, 4.6 Hz) performed significantly (P < 0.001) better than first‐order (16.5 Hz) and iterative shimming (18 Hz) and the water peak linewidth was significantly reduced using PFC pads (P < 0.001). Using second‐order shimming and PFC pads, CSI was successful in 10 patients with nodal metastases (n = 8) and benign tumors (n = 2) and unsuccessful in four patients with primary tumors along the aerodigestive tract.

Conclusion

Proton CSI can be successfully performed in the head and neck using second‐order shimming and PFC pads to correct air and tissue susceptibility differences. CSI was more successfully performed on nodal metastases, while CSI for primary tumors along the aerodigestive tract remains a challenge. J. Magn. Reson. Imaging 2010;32:1248–1254. © 2010 Wiley‐Liss, Inc.     

Intravoxel incoherent motion perfusion imaging in acute stroke: initial clinical experience

Introduction

Intravoxel incoherent motion (IVIM) imaging is an MRI perfusion technique that uses a diffusion-weighted sequence with multiple b values and a bi-compartmental signal model to measure the so-called pseudo-diffusion of blood caused by its passage through the microvascular network. The goal of the current study was to assess the feasibility of IVIM perfusion fraction imaging in patients with acute stroke.

Methods

Images were collected in 17 patients with acute stroke. Exclusion criteria were onset of symptoms to imaging >5 days, hemorrhagic transformation, infratentorial lesions, small lesions <0.5 cm in minimal diameter and hemodynamic instability. IVIM imaging was performed at 3 T, using a standard spin-echo Stejskal-Tanner pulsed gradients diffusion-weighted sequence, using 16 b values from 0 to 900 s/mm². Image quality was assessed by two radiologists, and quantitative analysis was performed in regions of interest placed in the stroke area, defined by thresholding the apparent diffusion coefficient maps, as well as in the contralateral region.

Results

IVIM perfusion fraction maps showed an area of decreased perfusion fraction f in the region of decreased apparent diffusion coefficient. Quantitative analysis showed a statistically significant decrease in both IVIM perfusion fraction f (0.026?±?0.019 vs. 0.056?±?0.025, p?=?2.2?·?10^?6) and diffusion coefficient D compared with the contralateral side (3.9?±?0.79?·?10^?4 vs. 7.5?±?0.86?·?10^?4 mm²/s, p?=?1.3?·?10^?20).

Conclusion

IVIM perfusion fraction imaging is feasible in acute stroke. IVIM perfusion fraction is significantly reduced in the visible infarct. Further studies should evaluate the potential for IVIM to predict clinical outcome and treatment response.     

Comparison of 3 Tesla proton MR spectroscopy, MR perfusion and MR diffusion for distinguishing glioma recurrence from posttreatment effects

Purpose:

To compare 3 Tesla (3T) multi‐voxel and single‐voxel proton MR spectroscopy (MRS), dynamic susceptibility contrast perfusion MRI (DSC), and diffusion‐weighted MRI (DWI) for distinguishing recurrent glioma from postradiation injury.

Materials and Methods:

We reviewed all 3T MRS, DSC and DWI studies performed for suspicion of malignant glioma recurrence between October 2006 and December 2008. Maximum Cho/NAA and Cho/Cr peak‐area and peak‐height ratios were recorded for both multi‐voxel and single‐voxel MRS. Maximum cerebral blood volume (CBV) and minimum apparent diffusion coefficient (ADC) were normalized to white matter. Histopathology and clinical‐radiologic follow‐up served as reference standards. Receiver operating characteristic curves for each parameter were compared.

Results:

Forty lesions were classified as glioma recurrence (n = 30) or posttreatment effect (n = 10). Diagnostic performance was similar for CBV ratio (AUC = 0.917, P < 0.001), multi‐voxel Cho/Cr peak‐area (AUC = 0.913, P = 0.002), and multi‐voxel Cho/NAA peak‐height (AUC = 0.913, P = 0.002), while ADC ratio (AUC = 0.726, P = 0.035) did not appear to perform as well. Single‐voxel MRS parameters did not reliably distinguish tumor recurrence from posttreatment effects.

Conclusion:

A 3T DSC and multi‐voxel MRS Cho/Cr peak‐area and Cho/NAA peak‐height appear to outperform DWI for distinguishing glioma recurrence from posttreatment effects. Single‐voxel MRS parameters do not appear to distinguish glioma recurrence from posttreatment effects reliably, and therefore should not be used in place of multi‐voxel MRS. J. Magn. Reson. Imaging 2012;35:56‐63. © 2011 Wiley Periodicals, Inc.     

Intravoxel incoherent motion diffusion-weighted MR imaging in differentiation of lung cancer from obstructive lung consolidation: comparison and correlation with pharmacokinetic analysis from dynamic contrast-enhanced MR imaging

Objectives

To test whether parameters derived from intravoxel incoherent motion (IVIM) can be used to distinguish lung cancer from obstructive pulmonary consolidation by comparing them with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI)-derived parameters and to evaluate the correlation between these quantitative parameters.

Methods

A total of 31 lung cancer patients, confirmed by pathology and obstructive consolidations confirmed by positron emission tomography/computed tomography (PET-CT), were recruited. All of them were assessed with structural MRI and IVIM and 17 of them underwent additional DCE-MRI examinations. Parameters derived from IVIM and DCE-MRI in the tumour and consolidation were analysed, and the optimal cut-off values in differential diagnosis were obtained.

Results

ADC_total, D and f values were lower (P?<?0.05), while IAUC₆₀ was higher in lung cancers (P?=?0.013) compared with obstructive pulmonary consolidations. According to the ROC curve, ADC_total outperformed other perfusion and diffusion parameters with the optimal cut-off value of 1.409?×?10^-3 mm²/s (AUC?=?0.95). Poor correlations were found between parameters derived from IVIM and DCE-MRI.

Conclusions

IVIM-MRI is potentially useful in the differentiation of lung cancer and obstructive pulmonary consolidation. ADC_total, D and f may be reliable independent discriminating markers, but D ^* is variable with low diagnostic accuracy.

Key Points

? Lung cancer and consolidation differentiation is essential for treatment decision-making. ? Perfusion and diffusion characteristics of lesions could help differential diagnosis. ? IVIM can separate reflection of tissue diffusivity and microcapillary perfusion. ? The relationship between perfusion quantified by IVIM and DCE-MRI is controversial.     

Can the IVIM model be used for renal perfusion imaging?

Objective: Renal perfusion imaging may provide information about the hemodynamic significance of a renal artery stenosis and could improve noninvasive characterization when combined with angiography. It was proposed previously that diffusion sequences could provide useful perfusion indices based on the intravoxel incoherent motion (IVIM) model. Owing to motion artifacts, diffusion imaging has been restricted to relatively immobile organs like the brain. With the availability of single-shot echo-planar imaging (EPI) our purpose was to evaluate the IVIM model in renal perfusion. Methods and material: Eight volunteers underwent diffusion-sensitive magnetic resonance (MR) imaging of the kidneys using a spin echo (SE) EPI sequence. The diffusion coefficients determined by a linear regression analysis and fits to the IVIM function were calculated. Results and conclusion: Our preliminary experience does not support the possibility of obtaining perfusion information using the IVIM model in the kidneys.     

Intravoxel incoherent motion MR imaging measurements of the bilateral parotid glands at 3.0-T MR: effect of age,gender and laterality in healthy adults

Objective:

To investigate the effect of age, gender and laterality on the intravoxel incoherent motion (IVIM) MR imaging measurements of parotid glands in healthy participants at 3.0-T MRI.

Methods:

A total of 108 healthy participants were prospectively recruited. IVIM MRI scan was performed using a 3.0-T MR scanner, and corresponding parameters (perfusion fraction, f; pseudodiffusion coefficient, D*; tissue diffusivity, D) were derived from biexponential fitting of IVIM data. Pearson correlation analysis was performed to determine the association between the IVIM MRI parameters and age. The parameter difference between male and female participants or between left and right parotid glands was compared using unpaired or paired t test, respectively.

Results:

Excellent interreader and intrareader agreements on the measurements of IVIM MRI parameters were achieved. Both D and f values correlated inversely with the age in both left and right parotid glands (p < 0.05) while D* value did not (p > 0.05). Male participants had higher IVIM MRI parameters than the female participants in both left and right glands (p < 0.05). No significant differences were found in the IVIM MRI parameters between left and right glands in both male and female participants (p > 0.05).

Conclusion:

The IVIM MRI parameters are age and gender dependent, but not laterality dependent. Age- and gender-related effect should be taken into consideration in future IVIM MRI studies for parotid glands.

Advances in knowledge:

(1) Both D and f values correlated inversely with the age in healthy parotid glands, while D* value did not. (2) The parotid glands of males showed higher IVIM MRI parameters than that of females. (3) There were no significant differences on the IVIM MRI parameters between the left and right glands. (4) Age- and gender-related effect should be taken into consideration in future IVIM MRI studies for parotid glands.     

Intravoxel incoherent motion MR imaging for breast lesions: comparison and correlation with pharmacokinetic evaluation from dynamic contrast-enhanced MR imaging

Objectives

To compare diagnostic performance for breast lesions by quantitative parameters derived from intravoxel incoherent motion (IVIM) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) and to explore whether correlations exist between these parameters.

Methods

IVIM and DCE MRI were performed on a 1.5-T MRI scanner in patients with suspicious breast lesions. Thirty-six breast cancers and 23 benign lesions were included in the study. Quantitative parameters from IVIM (D, f and D*) and DCE MRI (K^trans, K_ep, V_e and V_p) were calculated and compared between malignant and benign lesions. Spearman correlation test was used to evaluate correlations between them.

Results

D, f, D* from IVIM and K^trans, K_ep, V_p from DCE MRI were statistically different between breast cancers and benign lesions (p?<?0.05, respectively) and D demonstrated the largest area under the receiver-operating characteristic curve (AUC?=?0.917) and had the highest specificity (83 %). The f value was moderately statistically correlated with V_p (r?=?0.692) and had a poor correlation with K^trans (r?=?0.456).

Conclusions

IVIM MRI is useful in the differentiation of breast lesions. Significant correlations were found between perfusion-related parameters from IVIM and DCE MRI. IVIM may be a useful adjunctive tool to standard MRI in diagnosing breast cancer.

Key Points

? IVIM provided diffusion as well as perfusion information ? IVIM could help differential diagnosis of breast lesions ? Correlations were found between perfusion-related parameters from IVIM and DCE MRI

     

Evolution of hyperacute stroke over 6 hours using serial MR perfusion and diffusion maps

Purpose

To develop an appropriate method to evaluate the time‐course of diffusion and perfusion changes in a clinically relevant animal model of ischemic stroke and to examine lesion progression on MR images. An exploration of acute stroke infarct expansion was performed in this study by using a new methodology for developing time‐to‐infarct maps based on the time at which each voxel becomes infarcted. This enabled definition of homogeneous regions from the heterogeneous stroke infarct.

Materials and Methods

Time‐to‐infarct maps were developed based on apparent diffusion coefficient (ADC) changes. These maps were validated and then applied to blood flow and time‐to‐peak maps to examine perfusion changes.

Results

ADC stroke infarct showed different evolution patterns depending on the time at which that region of tissue infarcted. Applying the time‐to‐infarct maps to the perfusion maps showed localized perfusion evolution characteristics. In some regions, perfusion was immediately affected and showed little change over the experiment; however, in some regions perfusion changes were more dynamic.

Conclusion

Results were consistent with the diffusion‐perfusion mismatch hypothesis. In addition, characteristics of collateral recruitment were identified, which has interesting stroke pathophysiology and treatment implications. J. Magn. Reson. Imaging 2009;29:1262–1270. © 2009 Wiley‐Liss, Inc.     

Liver fibrosis: an intravoxel incoherent motion (IVIM) study

Purpose:

To characterize longitudinal changes in molecular water diffusion, blood microcirculation, and their contributions to the apparent diffusion changes using intravoxel incoherent motion (IVIM) analysis in an experimental mouse model of liver fibrosis.

Materials and Methods:

Liver fibrosis was induced in male adult C57BL/6N mice (22–25 g; n = 12) by repetitive dosing of carbon tetrachloride (CCl₄). The respiratory‐gated diffusion‐weighted (DW) images were acquired using single‐shot spin‐echo EPI (SE‐EPI) with 8 b‐values and single diffusion gradient direction. True diffusion coefficient (D_true), blood pseudodiffusion coefficient (D_pseudo), and perfusion fraction (P_fraction) were measured. Diffusion tensor imaging (DTI) was also performed for comparison. Histology was performed with hematoxylin‐eosin and Masson's trichrome staining.

Results:

A significant decrease in D_true was found at 2 weeks and 4 weeks following CCl₄ insult, as compared with that before insult. Similarly, D_pseudo values before injury was significantly higher than those at 2 weeks and 4 weeks after CCl₄ insult. Meanwhile, P_fraction values showed no significant differences over different timepoints. For DTI, significant decrease in ADC was observed following CCl₄ administration. Fractional anisotropy at 2 weeks after CCl₄ insult was significantly lower than that before insult, and subsequently normalized at 4 weeks after the insult. Liver histology showed collagen deposition, the presence of intracellular fat vacuoles, and cell necrosis/apoptosis in livers with CCl₄ insult.

Conclusion:

Both molecular water diffusion and blood microcirculation contribute to the alteration in apparent diffusion changes in liver fibrosis. Reduction in D_true and D_pseudo values resulted from diffusion and perfusion changes, respectively, during the progression of liver fibrosis. IVIM analysis may serve as valuable and robust tool in detecting and characterizing liver fibrosis at early stages, monitoring its progression in a noninvasive manner. J. Magn. Reson. Imaging 2012;36:159–167. © 2012 Wiley Periodicals, Inc.     

Perfusion and diffusion characteristics of cervical cancer based on intraxovel incoherent motion MR imaging-a pilot study

Objectives

To investigate the tissue characteristics of cervical cancer based on the intravoxel incoherent motion (IVIM) model and to assess the IVIM parameters in tissue differentiation in the female pelvis.

Methods

Sixteen treatment-naïve cervical cancer and 17 age-matched healthy subjects were prospectively recruited for diffusion-weighted (b?=?0–1,000 s/mm²) and standard pelvic MRI. Bi-exponential analysis was performed to derive the perfusion parameters f (perfusion fraction) and D* (pseudodiffusion coefficient) as well as the diffusion parameter D (true molecular diffusion coefficient) in cervical cancer (n?=?16), normal cervix (n?=?17), myometrium (n?=?33) and leiomyoma (n?=?14). Apparent diffusion coefficient (ADC) was calculated. Kruskal–Wallis test and receiver operating characteristics (ROC) curves were used.

Results

Cervical cancer had the lowest f (14.9?±?2.6 %) and was significantly different from normal cervix and leiomyoma (p?<?0.05). The D (0.86?±?0.16 x 10^-3 mm2/s) was lowest in cervical cancer and was significantly different from normal cervix and myometrium (p?<?0.05) but not leiomyoma. No difference was observed in D*. D was consistently lower than ADC in all tissues. ROC curves indicated that f < 16.38 %, D < 1.04?×?10^-3 mm²/s and ADC < 1.13?×?10^-3 mm²/s could differentiate cervical cancer from non-malignant tissues (AUC 0.773–0.908).

Conclusions

Cervical cancer has low perfusion and diffusion IVIM characteristics with promising potential for tissue differentiation.

Key Points

? Diffusion-weighted MRI is increasingly applied in evaluation of cervical cancer. ? Cervical cancer has distinctive perfusion and diffusion characteristics. ? Intravoxel incoherent motion characteristics can differentiate cervical cancer from non-malignant uterine tissues.     

Arterial spin labeling perfusion MRI in pediatric arterial ischemic stroke: Initial experiences

Purpose

To investigate the feasibility and utility of arterial spin labeling (ASL) perfusion MRI for characterizing alterations of cerebral blood flow (CBF) in pediatric patients with arterial ischemic stroke (AIS).

Materials and Methods

Ten children with AIS were studied within 4 to 125 hours following symptom onset, using a pulsed ASL (PASL) protocol attached to clinically indicated MR examinations. The interhemisphere perfusion deficit (IHPD) was measured in predetermined vascular territories and infarct regions of restricted diffusion, which were compared with the degree of arterial stenosis and volumes of ischemic infarcts.

Results

Interpretable CBF maps were obtained in all 10 patients, showing simple lesion in nine patients (five hypoperfusion, two hyperperfusion, and two normal perfusion) and complex lesions in one patient. Both acute and follow‐up infarct volumes were significantly larger in cases with hypoperfusion than in either hyper‐ or normal perfusion cases. The IHPD was found to correlate with the degree of stenosis, diffusion lesion, and follow‐up T₂ infarct volumes. Mismatch between perfusion and diffusion lesions was observed. Brain regions presenting delayed arterial transit effects were tentatively associated with positive outcome.

Conclusion

This study demonstrates the clinical utility of ASL in the neuroimaging diagnosis of pediatric AIS. J. Magn. Reson. Imaging 2009;29:282–290. © 2009 Wiley‐Liss, Inc.     

Comparison of gadoxetic acid-enhanced dynamic imaging and diffusion-weighted imaging for the preoperative evaluation of colorectal liver metastases

Purpose:

To retrospectively compare the diagnostic accuracy for the detection of colorectal liver metastases between gadoxetic acid‐enhanced MRI (EOB‐MRI) and diffusion‐weighted imaging (DWI) on 3.0 Tesla (T) system, and then to determine whether a combination of the two techniques may improve the diagnostic performance.

Materials and Methods:

Forty‐seven patients underwent MR imaging at 3.0T, including DWI (DWI set) and dynamic and hepatobiliary phase EOB‐MRI (EOB set) for the preoperative evaluation of colorectal liver metastases. All suspicious metastases were confirmed by hepatic surgery. Two blinded readers independently reviewed three different image sets, which consisted of DWI set, EOB set, and combined set. The accuracy was assessed by the area (Az) under the alternative‐free response receiver operating characteristic curve, and the sensitivity and positive predictive value (PPV) were calculated.

Results:

We found a total of 78 confirmed colorectal liver metastases in 42 of 47 patients. Each reader noted higher diagnostic accuracy of combined set of EOB‐MRI and DWI than DWI set and EOB set, without statistical significance. Regardless of the size of colorectal liver metastasis, each reader detected significantly more metastases on combined set than on DWI set, and PPV was significantly higher with DWI set than with EOB set or with combined set for one reader.

Conclusion:

EOB‐MRI was more useful for the detection of colorectal liver metastases, while DWI was more useful for their characterization. The combination of EOB‐MRI and DWI showed significantly higher accuracy and sensitivity for the preoperative detection of small colorectal liver metastases than DWI. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Fast Dixon whole-body MRI for detecting distant cancer metastasis: a preliminary clinical study

Purpose:

To evaluate the feasibility of fast Dixon whole‐body (WB) magnetic resonance imaging (MRI) for detecting bone and liver metastasis in clinical patients and to compare its performance with skeletal scintigraphy (SS) for detecting bone metastases using reference imaging with >1 year follow‐up as the gold standard.

Materials and Methods:

Twenty‐nine patients with bone metastases prospectively underwent WB MRI and SS. WB MRI included coronal T2, axial T1 with and without intravenous gadolinium (including triphasic liver sequences), and axial diffusion‐weighted imaging, plus spinal sagittal postcontrast T1‐weighted images. The skeleton was divided into 16 segments. Reviewers blinded to other images identified up to five lesions per segment and rated them using a five‐point confidence scale for metastatic disease. Sensitivities and specificities were compared using the McNemar test.

Results:

The sensitivity of WB MRI and SS in detecting bone metastases was 70.8% and 59.6% (P = 0.003), respectively; specificity was 89.1% and 98.7% (P < 0.0001). WB MRI detected all livers with metastases (n = 8). One focal nodular hyperplasia was classified as a metastasis on WB MRI.

Conclusion:

Fast Dixon WB MRI is feasible in clinical patients, highly specific, and more sensitive than SS in detecting bone metastases, and can detect metastases of the liver. J. Magn. Reson. Imaging 2012;399‐408. © 2011 Wiley Periodicals, Inc.     

Intravoxel incoherent motion MR imaging for prostate cancer: An evaluation of perfusion fraction and diffusion coefficient derived from different b‐value combinations

There has been a resurgent interest in intravoxel incoherent motion (IVIM) MR imaging to obtain perfusion as well as diffusion information on lesions, in which the diffusion was modeled as Gaussian diffusion. However, it was observed that this diffusion deviated from expected monoexponential decay at high b‐values and the reported perfusion in prostate is contrary to the findings in dynamic contrast‐enhanced (DCE) MRI studies and angiogenesis. Thus, this work is to evaluate the effect of different b‐values on IVIM perfusion fractions (f) and diffusion coefficients (D) for prostate cancer detection. The results show that both parameters depended heavily on the b‐values, and those derived without the highest b‐value correlated best with the results from DCE‐MRI studies; specifically, f was significantly elevated (7.2% vs. 3.7%) in tumors when compared with normal tissues, in accordance with the volume transfer constant (K^trans; 0.39 vs. 0.18 min^?1) and plasma fractional volume (v_p; 8.4% vs. 3.4%). In conclusion, it is critical to choose an appropriate range of b‐values in studies or include the non‐Gaussian diffusion contribution to obtain unbiased IVIM measurements. These measurements could eliminate the need for DCE‐MRI, which is especially relevant in patients who cannot receive intravenous gadolinium‐based contrast media. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Quantification of renal perfusion: comparison of arterial spin labeling and dynamic contrast-enhanced MRI

Purpose:

To provide the first comparison of absolute renal perfusion obtained by arterial spin labeling (ASL) and separable compartment modeling of dynamic contrast‐enhanced (DCE) magnetic resonance imaging (MRI). Moreover, we provide the first application of the dual bolus approach to quantitative DCE‐MRI perfusion measurements in the kidney.

Materials and Methods:

Consecutive ASL and DCE‐MRI acquisitions were performed on six rabbits on a 1.5 T MRI system. Gadolinium (Gd)‐DTPA was administered in two separate injections to decouple measurement of the arterial input function and tissue uptake curves. For DCE perfusion, pixel‐wise and mean cortex region‐of‐interest tissue curves were fit to a separable compartment model.

Results:

Absolute renal cortex perfusion estimates obtained by DCE and ASL were in close agreement: 3.28 ± 0.59 mL/g/min (ASL), 2.98 ± 0.60 mL/g/min (DCE), and 3.57 ± 0.96 mL/g/min (pixel‐wise DCE). Renal medulla perfusion was 1.53 ± 0.35 mL/g/min (ASL) but was not adequately described by the separable compartment model.

Conclusion:

ASL and DCE‐MRI provided similar measures of absolute perfusion in the renal cortex, offering both noncontrast and contrast‐based alternatives to improve current renal MRI assessment of kidney function. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Measurement reproducibility of perfusion fraction and pseudodiffusion coefficient derived by intravoxel incoherent motion diffusion-weighted MR imaging in normal liver and metastases

Objective

To determine the measurement reproducibility of perfusion fraction f, pseudodiffusion coefficient D ^* and diffusion coefficient D in colorectal liver metastases and normal liver.

Methods

Fourteen patients with known colorectal liver metastases were examined twice using respiratory-triggered echo-planar DW-MRI with eight b values (0 to 900 s/mm²) 1 h apart. Regions of interests were drawn around target metastasis and normal liver in each patient to derive ADC (all b values), ADC_high (b values ≥100 s/mm²) and intravoxel incoherent motion (IVIM) parameters f, D ^* and D by least squares data fitting. Short-term measurement reproducibility of median ADC, ADC_high, f, D ^* and D values were derived from Bland–Altman analysis.

Results

The measurement reproducibility for ADC, ADC_high and D was worst in colorectal liver metastases (?21 % to +25 %) compared with liver parenchyma (?6 % to +8 %). Poor measurement reproducibility was observed for the perfusion-sensitive parameters of f (?75 % to +241 %) and D ^* (?89 % to +2,120 %) in metastases, and to a lesser extent the f (?24 % to +25 %) and D* (?31 % to +59 %) of liver.

Conclusions

Estimates of f and D ^* derived from the widely used least squares IVIM fitting showed poor measurement reproducibility. Efforts should be made to improve the measurement reproducibility of perfusion-sensitive IVIM parameters.

Key Points

? Quantitative diffusion-weighted MRI parameters are increasingly used for clinical management decisions. ? However perfusion-sensitive intravoxel incoherent motion (IVIM) parameters showed poor measurement reproducibility. ? Measurement reproducibility of IVIM parameters was worse in metastases than normal liver. ? Efforts to improve measurement reproducibility of IVIM parameters should be explored.