Pure Diffusion Coefficient Research Articles

Investigation of Apparent Diffusion Coefficient from Ultra-high b-Values in Parkinson's Disease.

To assess brain damage in Parkinson's disease (PD) based on apparent diffusion coefficient (ADC) data obtained from ultra-high b-values. Eighteen PD patients and 18 controls received diffusion-weighted imaging (DWI) with standard b-values (0, 1,000 s/mm(2)) and 15 b-values (0-5,000 s/mm(2)). Standard ADC (ADCst) maps were calculated from standard b-values, while maps of pure diffusion coefficients (D), pseudo-diffusion coefficients (D(*)), and ultra-high ADCs (ADCuh) were calculated from the 15 b-values using a tri-component model. In this model, D and D(*) values were quantified with a bi-exponential equation using b-values less than 2,000 s/mm(2), while ADCuh was quantified by fitting the signals at ultra-high b-values (2,000-5,000 s/mm(2)) to the mono-exponential equation. ADCst, ADCuh, D, and D(*) of the globus pallidus (GP), putamen (P), and substantia nigra (SN) were compared between PD patients and normal control subjects. ADCuh of the GP, P, and SN was significantly lower in PD patients than those in control subjects (P < 0.001), while ADCst, D, and D(*) of the GP, P and SN were not different between the two groups (P > 0.05). ADCuh may be a useful measurement for evaluating brain damage in PD patients. • DWI with ultra-high b-values may provide new insight into Parkinson's disease pathology • ADC calculated using ultra-high b-values is different between PD and controls • ADC uh may be associated with water transportation by aquaporins.

The activity and radial dependence of anomalous diffusion by pitch angle scattering on split magnetic drift shells

AbstractAsymmetries in the magnetospheric magnetic field produce drift shell splitting, which causes the radial (drift shell) invariant to sometimes depend on pitch angle. Where drift shell splitting is significant, pitch angle scattering leads to diffusion in all three invariants of the particle's motion, including cross diffusion. We examine the magnitude of drift shell splitting‐related anomalous diffusion for outer zone electrons compared to conventional diffusion in the absence of drift shell splitting. We assume that the primary local scattering process is wave‐particle interactions with chorus. We find that anomalous radial diffusion can exceed that of conventional drift‐resonant radial diffusion for particles with energies near 0.1 MeV at all radial distances outside the plasmasphere during quiet to moderate geomagnetic activity, and it is significant at 0.5 MeV. Cross diffusion involving the radial invariant can exceed the geometric mean of the corresponding pure diffusion coefficients at 0.1 MeV, and that such cross diffusion is significant even at 0.5–1 MeV. At 1 MeV, cross diffusion is often significant. The highest radial distances and magnetic activity levels in our study do not always exhibit as much significant anomalous diffusion as moderate radial distances and activity levels. This can be explained by (a) stronger dependence of conventional diffusion on magnetic activity and radius, and (b) strongest drift shell splitting at moderate magnetic activity. Simulation codes that neglect the possibility for cross terms will likely systematically underperform, especially for 0.1–0.5 MeV electrons, for much of the outer zone for quiet to moderate levels of magnetic activity.

Decreases in molecular diffusion, perfusion fraction and perfusion-related diffusion in fibrotic livers: a prospective clinical intravoxel incoherent motion MR imaging study.

PurposeThis study was aimed to determine whether pure molecular-based diffusion coefficient (D) and perfusion-related diffusion parameters (perfusion fraction f, perfusion-related diffusion coefficient D*) differ in healthy livers and fibrotic livers through intra-voxel incoherent motion (IVIM) MR imaging.Material and Methods17 healthy volunteers and 34 patients with histopathologically confirmed liver fibrosis patients (stage 1 = 14, stage 2 = 8, stage 3& 4 = 12, METAVIR grading) were included. Liver MR imaging was performed at 1.5-T. IVIM diffusion weighted imaging sequence was based on standard single-shot DW spin echo-planar imaging, with ten b values of 10, 20, 40, 60, 80, 100, 150, 200, 400, 800 sec/mm2 respectively. Pixel-wise realization and regions-of-interest based quantification of IVIM parameters were performed.Results D, f, and D* in healthy volunteer livers and patient livers were 1.096±0.155 vs 0.917±0.152 (10−3 mm2/s, p = 0.0015), 0.164±0.021 vs 0.123±0.029 (p<0.0001), and 13.085±2.943 vs 9.423±1.737 (10−3 mm2/s, p<0.0001) respectively, all significantly lower in fibrotic livers. As the fibrosis severity progressed, D, f, and D* values decreased, with a trend significant for f and D*.ConclusionFibrotic liver is associated with lower pure molecular diffusion, lower perfusion volume fraction, and lower perfusion-related diffusion. The decrease of f and D* in the liver is significantly associated liver fibrosis severity.

Simple and reliable determination of intravoxel incoherent motion parameters for the differential diagnosis of head and neck tumors.

Intravoxel incoherent motion (IVIM) imaging can characterize diffusion and perfusion of normal and diseased tissues, and IVIM parameters are authentically determined by using cumbersome least-squares method. We evaluated a simple technique for the determination of IVIM parameters using geometric analysis of the multiexponential signal decay curve as an alternative to the least-squares method for the diagnosis of head and neck tumors. Pure diffusion coefficients (D), microvascular volume fraction (f), perfusion-related incoherent microcirculation (D*), and perfusion parameter that is heavily weighted towards extravascular space (P) were determined geometrically (Geo D, Geo f, and Geo P) or by least-squares method (Fit D, Fit f, and Fit D*) in normal structures and 105 head and neck tumors. The IVIM parameters were compared for their levels and diagnostic abilities between the 2 techniques. The IVIM parameters were not able to determine in 14 tumors with the least-squares method alone and in 4 tumors with the geometric and least-squares methods. The geometric IVIM values were significantly different (p<0.001) from Fit values (+2±4% and −7±24% for D and f values, respectively). Geo D and Fit D differentiated between lymphomas and SCCs with similar efficacy (78% and 80% accuracy, respectively). Stepwise approaches using combinations of Geo D and Geo P, Geo D and Geo f, or Fit D and Fit D* differentiated between pleomorphic adenomas, Warthin tumors, and malignant salivary gland tumors with the same efficacy (91% accuracy = 21/23). However, a stepwise differentiation using Fit D and Fit f was less effective (83% accuracy = 19/23). Considering cumbersome procedures with the least squares method compared with the geometric method, we concluded that the geometric determination of IVIM parameters can be an alternative to least-squares method in the diagnosis of head and neck tumors.

Value of multiple b-value diffusion-weighted imaging for differentiation of benign and malignant pulmonary masses

To explore the value of multiple b-value diffusion-weighted imaging (DWI) for differentiation of benign and malignant pulmonary masses. Thirty-eight patients were examined by routine sequences and DWI pulse sequence. DWI was acquired through a single-shot echo-planar imaging combined with a respiratory-triggered mode and parallel acquisition. Nine b values ranging from 0 to 1500 s/mm(2) (0, 50, 100, 150, 200, 400, 600, 1000, 1500 s/mm(2)) were used. The intravoxel incoherent motion model was applied to estimate pure diffusion coefficient D, perfusion-related diffusion coefficient D(*), and perfusion fraction f. Mann-Whitney U test was used to compare all measured parameters between benign and malignant groups. The diagnostic performance of the related parameters was evaluated with receiver operating characteristics (ROC) analysis. Of these 38 patients, 30 were pathologically confirmed and 8 were diagnosed based on clinical data. There were 23 lung malignant masses and 15 benign lesions. A significant reduction of D was found in malignant group than in benign group (Z=3.308, P=0.001), while no significant differences in D(*)(Z=1.646, P=0.100) and f(Z=1.254, P=0.210) were observed between the two groups. The area under the ROC curve for D value (0.839) was largest. When the cutoff value was selected as 0.90×10(-3) mm(2)/s, the sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of diagnosing malignant masses were 95.7%, 80.0%, 90.9%, 91.7%, and 88.9%,respectively. The D value in multiple b-value DWI has certain significance in differentiating the benign and malignant pulmonary masses and has the best diagnostic efficiency.

Intravoxel Incoherent Motion Diffusion-weighted MR Imaging of the Liver: Effect of Triggering Methods on Regional Variability and Measurement Repeatability of Quantitative Parameters

To compare the influence of triggering methods for diffusion-weighted imaging (DWI) on apparent diffusion coefficient (ADC) and intravoxel incoherent motion (IVIM) parameters in the liver, as well as regional variability and measurement repeatability. In this institutional review board-approved prospective study, 12 healthy volunteers (six women, six men; mean age, 30 years) underwent 1.5-T DWI of the liver by using nine b values twice with free breathing (FB) without triggering (mean acquisition time ± standard deviation, 3.7 minutes ± 0), respiratory triggering (RT) (mean acquisition time, 6.8 minutes ± 1.4), and echocardiography triggering (ET) (mean acquisition time, 8.3 minutes ± 2.0) after providing written informed consent. ADC and IVIM parameters, including pure diffusion coefficient (D), perfusion fraction (f), and perfusion-related diffusion coefficient (D*), were measured by using 15 regions of interest (ROIs). Regional variability of ADC and IVIM parameters and measurement repeatability were evaluated by using the coefficient of variation (CV) across ROIs and within-subject CV, respectively. ET DWI (range of CV across ROIs, 6.69%-20.0%) resulted in significantly decreased regional variability of ADC, D, and f, compared with FB DWI (13.86%-35.8%) and RT DWI (15.15%-35.91%, P ≤. 049). ET DWI showed better repeatability of ADC measurement (within-subject CV range, 3.17%-4.12% for ET DWI; 4.15%-4.74% for FB DWI; and 2.33%-6.96% for RT DWI), D (4.05%-5.34% for ET DWI, 4.11%-12.51% for FB DWI, and 3.19%-16.17% for RT DWI), and f (7.6%-9.86% for ET DWI, 13.83%-16.81% for FB DWI, and 10.05%-12.10% for RT DWI), compared with FB DWI and RT DWI, with significant differences in within-subject CV for D in the left hepatic lobe compared with RT DWI (P = .023) and for f compared with FB DWI (P ≤ .032). For all three imaging techniques, D* showed the worst repeatability (within-subject CV, 57.05%-156.61%) among ADC and IVIM parameters. ET DWI is more effective for decreasing regional variability of ADC and IVIM parameters than FB DWI or RT DWI; it may improve measurement repeatability by reducing cardiac motion-induced measurement error.

Intravoxel Incoherent Motion Magnetic Resonance Imaging of Oropharyngeal Cancer in Response to Chemoradiation Therapy

To investigate the utility of intravoxel incoherent motion (IVIM) MRI as a response indictor in human receiving chemoradiation therapy for oropharyngeal cancer. Eight male patients with histologically documented stage II/III squamous cell carcinoma of the oropharynx were included in this prospective study. IVIM-MRI was carried out at a 3.0-T GE MRI scanner using laterally placed 6-element flex coils. Patients were scanned twice; the first scan was at baseline prior to the start of radiation therapy (RT) and the second scan was at mid-treatment after delivery 30-55 Gy of RT. All patients were scanned in supine position with the same RT immobilization devices including individualized thermoplastic head and shoulder mask, customized mold, and dental stent to reduce motion artifacts and to improve image registration in longitudinal scans. IVIM parameters (D, pure diffusion coefficient; f, perfusion fraction; D*, pseudodiffusion coefficient) were calculated on a pixel-by-pixel basis using a bi-exponential model implemented within ImageJ with ten b-values ranging from 0-800 s/mm2. A fitting threshold of R2 > 0.5 was applied to all parametric maps. Based on post gadolinium T1-weighted images, tumors were contoured on IVIM maps for the purpose of comparing changes of IVIM parameters with tumor response. Paired-samples Wilcoxon signed rank test was used to compare IVIM parameters for assessment of treatment response. The mean IVIM parameters in pre-RT tumors were: D = 8.94 ± 1.67 (× 10-4 mm2/s), f = 0.23 ± 0.11, D* = 20.52 ± 9.71 (× 10-3 mm2/s); while those in mid-RT tumors were: D = 15.43 ± 3.68 (× 10-4 mm2/s), f = 0.34 ± 0.20, D* = 30.63 ± 8.47 (× 10-3 mm2/s). D and f were statistically significantly higher in mid-RT tumors (P < 0.005 and P < 0.02, respectively), while changes of D* in tumor tissues during RT were considered to be not significant at this sample size (P < 0.053). The preliminary results of this study show IVIM parameters change during RT. In particular, D and f are robust, useful clinical markers with a high level of confidence. On the other hand, D* also show potential feasibility in assessing treatment response. We continue to accrue study patients and to collect long-term clinical outcomes to corroborate the reproducibility and clinical significance of these pilot findings.

Intravoxel Incoherent Motion Diffusion-Weighted Imaging of Pancreatic Neuroendocrine Tumors

The purpose of this study was to assess the value of intravoxel incoherent motion and diffusion-weighted imaging for predicting the histologic grade of pancreatic neuroendocrine tumors (PNETs). Forty patients with surgically diagnosed PNETs who underwent preoperative magnetic resonance imaging, including diffusion-weighted imaging with a series of 10 b values (0-1000 s/mm(2), were included in this institutional review board-approved retrospective study. The apparent diffusion coefficient (ADC(total)), the intravoxel incoherent motion parameters (pure diffusion coefficient [D], pseudodiffusion coefficient [D(*)], and perfusion fraction [f]) were measured on the tumors. Histologic grading was performed on the basis of the World Health Organization 2010 classification system. Logistic regression analysis and receiver operating curve analysis were performed to identify the significant factors predicting the histologic grades. Grades 2 and 3 tumors were significantly larger than grade 1 tumors (average 3.62 cm vs 2.17 cm in diameter; P=0.001). Grades 2 and 3 tumors showed significantly lower D values than did grade 1 tumors (0.95 vs 1.21×10(-3) mm(2)/s; P=0.009), although the ADC(total) showed no significant difference. When any of the following 2 criteria was used, (a) tumor size smaller than 2.0 cm in diameter and (b) D value greater than 1.2×10(-3) mm(2)/s, the sensitivity, specificity, and positive predictive value for diagnosing grade 1 PNETs were 76.92%, 100%, and 100%, respectively. Pure diffusion coefficient (D) is possibly a better marker than ADC(total) is for differentiating grade 1 from grade 2 or 3 PNET and, combined with tumor size, can predict grade 1 PNET with a high specificity.

SU‐E‐QI‐05: Denoising Intravoxel Incoherent Motion Magnetic Resonance Images Using Non‐Local Mean Technique for Oropharyngeal Cancer Study

Purpose:Intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) normally shows a low signal to noise ratio (SNR) due to the presence of noise which complicates and biases the estimation of quantitative diffusion parameters. In this study, a Non‐local Means (NLM) approach was applied to remove the noise in oropharyngeal cancer IVIMMRI images.Methods:Eight male patients with squamous cell carcinoma of the oropharynx were included in this study under an approved IRB protocol. IVIM‐MRI was carried out on a 3.0‐T GE MRI. NLM denoising technique was performed using the MIPAV (V7, NIH). IVIM parameters (D, pure diffusion coefficient; f, perfusion fraction; D*, pseudodiffusion coefficient) were calculated on a pixel‐by‐pixel basis using a bi‐exponential model implemented within ImageJ (V1.47, NIH) with ten b‐values ranging from 0 – 800 s/mm2. SNR with and without denoising processing was calculated and compared in tumor regions. The agreements of IVIM‐MRI parameters estimated between with and without NLM processing in tumor region were assessed by Bland‐Altman plots.Results:Examples of IVIM images (b=800 s/mm2) and parametric maps (D, D* and f) with and without NLM applied are illustrated in Fig. 1 for an oropharynx cancer patient. Results of SNR and IVIM diffusion parameters between two different processing, as mean and standard deviation on 8 patients, are reported in Table 1. Bland‐Altman plots (Fig. 2) between the two approaches show better concordance for D (0.22% ± 1.42%) and f (0.56% ± 3.49%), whereas larger discrepancies were found for D* (0.86% ± 6.25%).Conclusion:NLM approach gives better SNR and quantitative data quality, also shows a good agreement between the IVIM parameters processed with and without NLM approaches. Therefore, NLM denoising technique can be applied to improve performance in terms of denoising quality and estimation of IVIM parameter as a post‐processing step without increasing the scanning time.

New experimental method to measure pure and cross diffusion coefficients of transparent ternary mixtures using Mach–Zehnder interferometry

In this study, a Mach–Zehnder interferometer that is equipped with two lasers of different wavelengths was used to conduct high resolution measurements of concentration profiles of a ternary mixture inside a diffusion cell. Windowed Fourier transform along with an advanced unwrapping procedure was employed to extract the phase image from fringe images. Then the phase difference was obtained for a spatial resolution of 1920×1240. According to the measured refractive index profile, concentration contours of two components (out of three) were measured. Consequently, the concentration profile of the third components was calculated. Previously, the analytical solution for binary mixtures was used to estimate only the pure diffusion coefficients. In this study, for the first time, the refractive indices measured by two lasers along with the analytical solution for the ternary system, based on Fick׳s law, and an evolutionary algorithm (EA) known as a genetic algorithm (GA) were employed to measure the pure and cross diffusion coefficients of a transparent ternary mixture simultaneously. The optimization method to estimate diffusion coefficients was tested against various objective functions, and the best approach was that which was proposed herein. In order to validate the proposed measurement method, the experimental results of the Selectable Optical Diagnostics Instrument-Diffusion Coefficients in Mixtures (SODI-DCMIX1 project) on board the International Space Station (ISS) were analyzed using this technique and the obtained results were compared with previous techniques.

Early radiation‐induced changes evaluated by intravoxel incoherent motion in the major salivary glands

To investigate the potential of intravoxel incoherent motion (IVIM) MRI for early evaluation of irradiated major salivary glands. Thirty-four patients with head-neck cancer were included in a prospective study. All patients underwent three serial IVIM-MRI: before, half-way through, and at the end of radiotherapy (RT). Apparent diffusion coefficient (ADC), ADClow derived in the low b-value range, perfusion fraction f, and pure diffusion coefficient D were estimated. Pretreatment values and early changes of diffusion parameters were correlated with parotid mean dose (Dmean ) and volume reduction after RT. Changes in diffusion parameters over time were all significant (P < 0.001 for ADC, ADClow , and D, P = 0.003 for f). Variations of ADC, ADClow , and f were not correlated with Dmean (P = 0.089, P = 0.252 and P = 0.884, respectively), whereas a significant relationship was found between changes in D and Dmean (r = 0.197 with CI95% = 0.004-0.375, P = 0.046). Pretreatment f and Dmean were the best independent predictors for the percentage shrinkage (P = 0.0003 and 0.0597 respectively; R(2) = 0.391). Early changes of irradiated major salivary glands can be noninvasively evaluated by IVIM-MRI. Perfusion-related coefficients in conjunction with dosimetric information increase our capability to predict the change in parotid volume and hence, if further validated, guide treatment strategy in RT.

Functional Multiparametric Magnetic Resonance Imaging of the Kidneys Using Blood Oxygen Level Dependent and Diffusion-Weighted Sequences

Little data are available on noninvasive magnetic resonance imaging based assessment of renal function during upper urinary tract obstruction. We determined whether functional multiparametric kidney magnetic resonance imaging could monitor the treatment response in cases of acute unilateral upper urinary tract obstruction. Between January 2008 and January 2010, 18 patients with acute unilateral upper urinary tract obstruction due to calculi were prospectively enrolled to undergo kidney magnetic resonance imaging with conventional, blood oxygen level dependent and diffusion-weighted sequences upon emergency hospital admission and after release of obstruction. We assessed functional imaging parameters of obstructed and contralateral unobstructed kidneys derived from blood oxygen level dependent (apparent spin relaxation rate) and diffusion-weighted (total apparent diffusion coefficient, pure diffusion coefficient and perfusion fraction) sequences during acute upper urinary tract obstruction and after its release. During acute obstruction the apparent spin relaxation rate and perfusion fraction were lower in the cortex (p=0.020 and 0.031) and medulla (p=0.012 and 0.190, respectively) of obstructed kidneys compared to contralateral unobstructed kidneys. After obstruction release the apparent spin relaxation rate and perfusion fraction increased in the cortex (p=0.016 and 0.004) and medulla (p=0.071 and 0.044, respectively) of formerly obstructed kidneys to values similar to those in contralateral kidneys. Total apparent diffusion coefficient and pure diffusion coefficient values did not significantly differ between obstructed and contralateral unobstructed kidneys during or after obstruction. In our patients with acute unilateral upper urinary tract obstruction due to calculi functional kidney magnetic resonance imaging using blood oxygen level dependent and diffusion-weighted sequences enabled us to monitor pathophysiological changes in obstructed kidneys during obstruction and after its release.

Intravoxel Incoherent Motion Imaging of Masticatory Muscles: Pilot Study for the Assessment of Perfusion and Diffusion During Clenching

The purpose of this study was to evaluate intravoxel incoherent motion (IVIM) imaging for assessing perfusion and diffusion of masticatory muscles during clenching. A prospective study was performed to assess the perfusion and diffusion of masticatory muscles during clenching. The masseter and medial pterygoid muscles participate in clenching, and the lateral pterygoids do not. IVIM parameters (microvascular volume fraction, f; pure diffusion coefficient, D; and perfusion-related incoherent microcirculation, D*) were determined on both the clenching and the balancing sides in 24 volunteers. The Wilcoxon test was used to compare the IVIM parameters at rest and during clenching. The f and D* values of the masseters significantly increased on the clenching side (f = 0.17 ± 0.10 vs 0.29 ± 0.11, p < 0.001; D* = 21.3 ± 18.5 × 10(-3) mm(2)/s vs 42.1 ± 33.3 × 10(-3) mm(2)/s, p = 0.0008). However, the D values did not change during clenching (1.26 ± 0.23 × 10(-3) mm(2) vs 1.21 ± 0.35 × 10(-3) mm(2)). The f values of the medial pterygoids also increased on the clenching side (0.20 ± 0.09 vs 0.30 ± 0.09, p < 0.001). On the balancing side, the f values of the masseters (0.19 ± 0.12 vs 0.30 ± 0.12, p < 0.001) and medial pterygoids (0.20 ± 0.09 vs 0.29 ± 0.11, p = 0.0007) significantly increased during clenching. In contrast, the IVIM values of the lateral pterygoids did not change. IVIM imaging may be useful for assessing perfusion and diffusion of the masticatory muscles.

Determination of Malignancy and Characterization of Hepatic Tumor Type With Diffusion-Weighted Magnetic Resonance Imaging

The objective of this study was to compare the value of the apparent diffusion coefficient (ADC) determined with 3 b values and the intravoxel incoherent motion (IVIM)-derived parameters in the determination of malignancy and characterization of hepatic tumor type. Seventy-six patients with 86 solid hepatic lesions, including 8 hemangiomas, 20 lesions of focal nodular hyperplasia, 9 adenomas, 30 hepatocellular carcinomas, 13 metastases, and 6 cholangiocarcinomas, were assessed in this prospective study. Diffusion-weighted images were acquired with 11 b values to measure the ADCs (with b = 0, 150, and 500 s/mm) and the IVIM-derived parameters, namely, the pure diffusion coefficient and the perfusion-related diffusion fraction and coefficient. The diffusion parameters were compared between benign and malignant tumors and between tumor types, and their diagnostic value in identifying tumor malignancy was assessed. The apparent and pure diffusion coefficients were significantly higher in benign than in malignant tumors (benign: 2.32 [0.87] × 10 mm/s and 1.42 [0.37] × 10 mm/s vs malignant: 1.64 [0.51] × 10 mm/s and 1.14 [0.28] × 10 mm/s, respectively; P < 0.0001 and P = 0.0005), whereas the perfusion-related diffusion parameters did not differ significantly between the 2 groups. The apparent and pure diffusion coefficients provided similar accuracy in assessing tumor malignancy (areas under the receiver operating characteristic curve of 0.770 and 0.723, respectively). In the multigroup analysis, the ADC was found to be significantly higher in hemangiomas than in hepatocellular carcinomas, metastases, and cholangiocarcinomas. In the same manner, it was higher in lesions of focal nodular hyperplasia than in metastases and cholangiocarcinomas. However, the pure diffusion coefficient was significantly higher only in hemangiomas versus hepatocellular and cholangiocellular carcinomas. Compared with the ADC, the diffusion parameters derived from the IVIM model did not improve the determination of malignancy and characterization of hepatic tumor type.

Assessment of diffusion parameters by intravoxel incoherent motion MRI in head and neck squamous cell carcinoma

The objectives of this study were to assess the diffusion parameters derived from intravoxel incoherent motion (IVIM) MRI in head and neck squamous cell carcinoma (HNSCC) and to investigate the agreement between different methods of tumor delineation and two numerical methods to extract the perfusion fraction f. Thirty-seven untreated patients with histopathologically confirmed primary HNSCC were included retrospectively in the study. The entire volume of the primary tumor was outlined on diffusion-weighted images using co-registered morphological images as a guide to the tumor location. Apparent diffusion coefficient (ADC) and IVIM diffusion parameters were estimated considering the largest tumor section as well as the entire tumor volume. A bi-exponential fit was implemented to extract f, D (pure diffusion coefficient) and D* (pseudo-diffusion coefficient). A second simplified method, based on an asymptotic extrapolation, was used to determine f. The agreement between ADC and IVIM diffusion parameters derived from the delineation of single and multiple slices, and between the two f estimations, was assessed by Bland-Altman plots. The inter-slice variability of ADC and IVIM diffusion parameters was evaluated. The Kruskal-Wallis test was used to investigate whether the tumor location had a statistically significant influence on the values of the parameters. Comparing the tumor delineation methods, a better accordance was found for ADC and D, with a mean percentage difference of less than 2%. Larger discrepancies were found for f and D*, with mean differences of 4.5% and 5.5%, respectively. When comparing the two f estimation methods, small mean differences were found (<3.5%), suggesting that the two methods may be considered as equivalent for the assessment of f in our patient population. The observed ADC and IVIM diffusion parameters were dependent on the anatomic site of the lesion, carcinoma of the nasopharynx showing more homogeneous and dissimilar estimations than other HNSCCs.

Intravoxel incoherent motion diffusion-weighted imaging in differential diagnosis of primary nasopharyngeal carcinoma and nasopharyngeal hyperplasia

Objective To investigate the feasibility of diffusion-weighted (DWI) MRIon basis of the intravoxel incoherent motion (IVIM) in nasopharyngeal carcinoma (NPC),and the diagnostic value of pure molecular diffusion coefficient (D),perfusion-related diffusion coefficient (D*) and perfusion fraction (f) in first onset NPC. Methods From December 2011 to January 2013,40 consecutive patients (26 men,14 women; median age,52 years) with suspected NPC were examined on a 3.0 T MR scanner.DW imaging was performed by using a single-shot echo-planar sequence with 13 b-values (0,10,20,30,50,80,100,150,200,300,400,600,800 s/mm2).MR imaging was compared with endoscopy and biopsy for the detection of NPC.Mean interval time between MR imaging examination and subsequent nasopharyngeal biopsy was 3 days (range,0—11 days).The subjects were divided into 2 groups according to the pathological results,group A was subjects with NPC (17 men,9 women; median age,35) and group B was ones with nasopharyngeal chronic hyperplastic inflammation (NPH) (9 men,5 women; median age,35).The D,D* and f were measured and compared in patients with first onset NPC and nasopharyngeal hyperplasia (Mann-Whitney test). Results IVIM DWI was successful in 24/26 with NPC and 12/14 with NPH.D value was Key words: Nasopharyngeal neoplasms; Diffusion magnetic resonance imaging; Diagnosis,differential

Are we ready to image the incoherent molecular motion in our minds?

The increasing radiological awareness about intravoxel incoherent motion imaging (IVIM) is reflected in this month’s issue of Neuroradiology. Hauser et al. [1] following hard on the heels of previous work [2] contribute substantially to the accumulating evidence for the utility of IVIM in tissue characterization. Several studies in abdominal imaging, where the theoretical principles of IVIM are verified in vivo in a satisfactory way [3], spearheaded the translation of IVIM into clinical applications after some time of hibernation. In human tissue, diffusion-weighted imaging (DWI) detects the molecular motion, which includes the molecular diffusion of water as well as the blood microcirculation in the capillary network. The cardinal DWIderived parameter, apparent diffusion coefficient, has been adapted over time to investigate the tissue-ofinterest but is dependent on the choice of b values and is endowed with a lumped and nonspecific character. The separation of pure diffusion from flow-related molecules motion demands complex models to describe the signal decay in DWI after application of increasing “motion probing” gradient intensities. The parameters D (tissue diffusivity or pure diffusion coefficient), D* (pseudodiffusion coefficient or perfusion-related incoherent microcirculation coefficient), and f (microvascular volume or perfusion fraction), which were dubbed by Le Bihan et al. [4] as the hallmarks of IVIM-sensitized DWI, seem to adequately resolve the perfusion (microcirculation or net flow) from the true diffusion given a sufficient b value sampling and a biexponential curve fit analysis. Almost simultaneous to the premier presentation of the IVIM technique, considerable skepticism was voiced concerning the suitability of f, D*, and fD* to measure perfusion in the “classical” sense of the term [5]. The debate remains ongoing and probably will not be terminated since it all seems to be a matter of definition. Actually, the rather loosely used term perfusion implies the efficiency of blood to saturate the tissue with oxygen and nutrients as well as to desaturate it from waste products. The monitoring of exogenous tracers (gadolinium compounds) by MRI provides the well-known blood flow parameter, which is conceptually related to perfusion. Diverse applied models rely on several assumptions that oversimplify the physiological background, resulting in an apparently meaningful determination of blood volume, which is not perfusion or blood flow. In contrast, IVIM devotees, by measuring the phase effects of flowing blood (endogenous marker), provide new insights into the capillary microcirculation, which may be conceptually related to “classical” perfusion under several assumptions about capillary network structure, too [6, 7]. Remarkably, the cellular shape/structuring may cause pseudo-perfusion like “guided flow” (for example in the kidney medulla or in the white brain matter). The apparent “overestimation” of perfusion fraction f compared to dynamic contrast-enhanced MR perfusion is inevitably influenced by the choice of motion-probing gradient directions versus the directionality of the neurons in the white matter. The bottom line is that the terms should bemeticulously chosen to avoid confusing imprecision that only serve to please our ears. Thus, before any further work clarifies these issues, it would be advisable to denominate f strictly as fractional volume of capillary flow instead of perfusion fraction. Whether IVIM launch means that “the end is nigh” for the contrast-enhanced perfusion-weighted MRI, the answer is probably not. The compartmental water exchange in the DWI experiments is not adequately captured due to the short evolution time (≈100 ms) compared to the dynamic contrastenhanced MRI, which tracks the intraand extravascular as This is a Comment to Original Article doi:10.1007/s00234-013-1154-9

Fat deposition decreases diffusion parameters at MRI: a study in phantoms and patients with liver steatosis

Assess the effect of fat deposition on the MRI diffusion coefficients in lipid emulsion-based phantoms and patients with proven isolated liver steatosis. Diffusion-weighted MRI with 11 b values from 0-500 s/mm(2) was performed in phantoms (fat fractions 0-18 %) with and without fat suppression and in 19 patients with normal liver (n = 14) or isolated liver steatosis (n = 5) proven by histopathology. The apparent, pure and perfusion-related diffusion coefficients and the perfusion fraction were measured. Spearman correlation coefficient and Mann-Whitney U test were used for comparisons. A strong correlation between the apparent and pure diffusion coefficients and fat fractions was seen in phantoms. The pure diffusion coefficient decreased significantly in patients with liver steatosis (0.96 ± 0.16 × 10(-3) mm(2)/s versus 1.18 ± 0.09 × 10(-3) mm(2)/s in normal liver, P = 0.005), whereas the decrease in apparent diffusion coefficient did not reach statistical significance (1.26 ± 0.25 × 10(-3) mm(2)/s versus 1.41 ± 0.14 × 10(-3) mm(2)/s in normal liver, P = 0.298). Fat deposition decreases the apparent and pure diffusion coefficients in lipid emulsion-based phantoms and patients with isolated liver steatosis proven by histopathology.

Diffusion-weighted MR Imaging for the Regional Characterization of Liver Tumors

To determine if diffusion-weighted (DW) magnetic resonance (MR) imaging with measurements of the apparent diffusion coefficient (ADC), pure diffusion coefficient, perfusion-related diffusion coefficient, and perfusion fraction can be used to differentiate between viable tumor and fibrous and necrotic regions within malignant liver tumors. The prospective study was approved by the institutional review board, and informed consent was obtained from all patients. Forty-eight patients with 51 malignant tumors were assessed. MR images of the liver were obtained by using DW imaging with 11 b factors (0-500 sec/mm(2)) and gadolinium-enhanced three-dimensional gradient-echo T1-weighted imaging. Tumors were segmented into viable tumor and fibrous and necrotic regions according to the enhancement pattern after injection of a nonspecific gadolinium chelate and, in surgically removed lesions, results of histopathologic correlation. The ADC, pure diffusion coefficient, perfusion-related diffusion coefficient, and perfusion fraction were calculated, and values were compared between viable tumor and fibrous and necrotic regions with the Kruskal-Wallis test followed by the Dunn multiple comparison test. The pure diffusion coefficient differed significantly between regions of viable tumor tissue and fibrosis (1.16 × 10(-3) mm(2)/sec ± 0.29 and 1.48 × 10(-3) mm(2)/sec ± 0.31, respectively; P = .016) and between regions of viable tumor tissue and necrosis (1.70 × 10(-3) mm(2)/sec ± 0.49, P = .002). There was a significantly lower perfusion fraction in necrotic regions (14% ± 6) than in viable tumor regions (21% ± 8, P = .005), but the perfusion fraction of the fibrous regions (21% ± 7) did not differ significantly from that of the other two regions. ADCs and perfusion-related diffusion coefficients did not differ significantly among the three regions. Results of this study show that viable tumor regions in malignant liver tumors can be differentiated from fibrous and necrotic regions with use of the pure diffusion coefficient but not with the other diffusion parameters.

Salivary Gland Tumors: Use of Intravoxel Incoherent Motion MR Imaging for Assessment of Diffusion and Perfusion for the Differentiation of Benign from Malignant Tumors

To prospectively evaluate the intravoxel incoherent motion (IVIM) parameters (microvascular volume fraction, f; pure diffusion coefficient, D; and perfusion-related incoherent microcirculation, D*) for differentiating between benign and malignant salivary gland tumors. All participants in this prospective institutional review board-approved study provided written informed consent. The perfusion and diffusion of 20 (65%) benign (12 pleomorphic adenomas and eight Warthin tumors) and 11 (35%) malignant salivary gland tumors were assessed on the basis of the IVIM theory. Diffusion-weighted magnetic resonance imaging was performed by using 11 b values (0-800 sec/mm(2)). The IVIM parameters of the salivary gland tumors were determined by a radiologist, and significant differences between the tumor types were assessed by using the Steel-Dwass test. The f values of Warthin tumors (0.156 ± 0.039 [standard deviation]) were significantly larger than those of pleomorphic adenomas (0.066 ± 0.031) (P = .003). The D values of malignant tumors (0.96 × 10(-3) mm(2)/sec ± 0.22) were significantly different from those of benign tumors (pleomorphic adenomas, 1.38 × 10(-3) mm(2)/sec ± 0.30 [P = .002]; Warthin tumors, 0.61 × 10(-3) mm(2)/sec ± 0.11 [P = .005]). The D* values of malignant tumors (21.99 × 10(-3) mm(2)/sec ± 19.01) were significantly smaller than those of Warthin tumors (42.64 × 10(-3) mm(2)/sec ± 20.17) (P = .022). The combination of D and D* criteria provided the best diagnostic accuracy (100%) for differentiation among the three tumor types. IVIM imaging may be helpful for differentiation between benign and malignant salivary gland tumors.