Diffusion-weighted MRI of ischemic stroke at 3T: Value of synthetic b-values

OBJECTIVES

Diffusion-weighted imaging (DWI) plays a crucial role in the diagnosis of ischemic stroke. We assessed the value of computed and acquired high b-value DWI in comparison with conventional b = 1000 s mm^-2 DWI for ischemic stroke at 3T.

METHODS

We included 36 patients with acute ischemic stroke who presented with diffusion abnormalities on DWI performed within 24 h of symptom onset. B-values of 0, 500, 1000 and 2000 s mm^-2 were acquired. Synthetic images with b-values of 1000, 1500, 2000 and 2500 s mm^-2 were computed. Two readers compared synthetic (syn) and acquired (acq) b = 2000 s mm^-2 images with acquired b = 1000 s mm^-2 images in terms of lesion detection rate, image quality, presence of uncertain hyperintensities and lesion conspicuity. Readers also selected their preferred b-value. Contrast ratio (CR) measurements were performed. Non-parametrical statistical tests and weighted Cohens' κ tests were computed.

RESULTS

Syn1000 and syn1500 matched acq1000 images in terms of lesion detection rate, image quality and presence of uncertain hyperintensities but presented with significantly improved lesion conspicuity (p < 0.01) and were frequently selected as preferred b-values. Acq2000 images exhibited a similar lesion detection rate and improved lesion conspicuity (p < 0.01) but worse image quality (p < 0.01) than acq1000 images. Syn2000 and syn2500 images performed significantly worse (p < 0.01) than acq1000 images in most or all categories. CR significantly increased with increasing b-values.

CONCLUSION

Synthetic images at b = 1000 and 1500 s mm^-2 and acquired DWI images at b = 2000 s mm^-2 may be of clinical value due to improved lesion conspicuity.

ADVANCES IN KNOWLEDGE

Synthetic b-values enable improved lesion conspicuity for DWI of ischemic stroke.

How to improve image quality of DWI of the prostate-enema or catheter preparation?

OBJECTIVES

To compare the impact of laxative enema preparation versus air/gas suction through a small catheter on image quality of prostate DWI.

METHODS

In this single-center study, 200 consecutive patients (100 in each arm) with either enema or catheter preparation were retrospectively included. Two blinded readers independently assessed aspects of image quality on 5-point Likert scales. Scores were compared between groups and the influence of confounding factors evaluated using multivariable logistic regression. Prostate diameters were compared on DWI and T₂-weighted imaging using intraclass correlation coefficients.

RESULTS

Image quality was significantly higher in the enema group regarding the severity of susceptibility-related artifacts (reader 1: 0.34 ± 0.77 vs. 1.73 ± 1.34, reader 2: 0.38 ± 0.86 vs. 1.76 ± 1.39), the differentiability of the anatomy (reader 1: 3.36 ± 1.05 vs. 2.08 ± 1.31, reader 2: 3.37 ± 1.05 vs. 2.09 ± 1.35), and the overall image quality (reader 1: 3.66 ± 0.77 vs. 2.26 ± 1.33, Reader 2: 3.59 ± 0.87 vs. 2.23 ± 1.38) with almost perfect inter-observer agreement (κ = 0.92-0.95). In the enema group, rectal distention was significantly lower and strongly correlated with the severity of artifacts (reader 1: ρ = 0.79, reader 2: ρ = 0.73). Furthermore, there were significantly fewer substantial image distortions, with odds ratios of 0.051 and 0.084 for the two readers which coincided with a higher agreement of the prostate diameters in the phase-encoding direction (0.96 vs. 0.89).

CONCLUSIONS

Enema preparation is superior to catheter preparation and yields substantial improvements in image quality.

KEY POINTS

• Enema preparation is superior to decompression of the rectum using air/gas suction through a small catheter. • Enema preparation markedly improves the image quality of prostate DWI regarding the severity of susceptibility-related artifacts, the differentiability of the anatomy, and the overall image quality and considerably reduces substantial artifacts that may impair a reliable diagnosis.

Amide proton transfer weighted (APTw) imaging based radiomics allows for the differentiation of gliomas from metastases

We sought to evaluate the utility of radiomics for Amide Proton Transfer weighted (APTw) imaging by assessing its value in differentiating brain metastases from high- and low grade glial brain tumors. We retrospectively identified 48 treatment-naïve patients (10 WHO grade 2, 1 WHO grade 3, 10 WHO grade 4 primary glial brain tumors and 27 metastases) with either primary glial brain tumors or metastases who had undergone APTw MR imaging. After image analysis with radiomics feature extraction and post-processing, machine learning algorithms (multilayer perceptron machine learning algorithm; random forest classifier) with stratified tenfold cross validation were trained on features and were used to differentiate the brain neoplasms. The multilayer perceptron achieved an AUC of 0.836 (receiver operating characteristic curve) in differentiating primary glial brain tumors from metastases. The random forest classifier achieved an AUC of 0.868 in differentiating WHO grade 4 from WHO grade 2/3 primary glial brain tumors. For the differentiation of WHO grade 4 tumors from grade 2/3 tumors and metastases an average AUC of 0.797 was achieved. Our results indicate that the use of radiomics for APTw imaging is feasible and the differentiation of primary glial brain tumors from metastases is achievable with a high degree of accuracy.

"I was seen by a radiologist, but unfortunately I can't remember the name and I still have questions. What should I do?" Radiologists should give thoughts to improve service professionalism and patient esteem

Background

The aim of the study is to investigate how well patients remember the radiologist’s name after a radiological examination, and whether giving the patient a business card improves the patient’s perception of the radiologist’s professionalism and esteem.

Methods

In this prospective and randomized two-centre study, a total of 141 patients with BI-RADS 1 and 2 scores were included. After screening examination comprising mammography and ultrasound by a radiologist, 71 patients received a business card (group 1), while 70 received no business card (group 2). Following the examination, patients were questioned about their experiences.

Results

The patients in group 1 could remember the name of the radiologist in 85% of cases. The patients in group 2, in contrast, could only remember the name in 7% of cases (p < 0.001). 90% of the patients in group 1 believed it was very important that they are able to contact the radiologist at a later time, whereas only 76% of patients in group 2 felt that this was a very important service (p < 0.025). A total of 87% of the patients in group 1 indicated that they would contact the radiologist if they had any questions whereas 73% of the patients in group 2 would like to contact the radiologist but were not able to do so, because they could not remember the name (p < 0.001).

All questions were analysed with a Cochran-Mantel-Haenszel (CMH) test that took study centre as stratification into account. In some cases, two categories were collapsed to avoid zero cell counts.

Conclusions

Using business cards significantly increased the recall of the radiologist’s name and could be an important tool in improving the relationships between patients and radiologists and enhancing service professionalism.

Trial registration

We have a general approval from our ethics committee. The patients have given their consent to this study.

Amide Proton Transfer Weighted Imaging Shows Differences in Multiple Sclerosis Lesions and White Matter Hyperintensities of Presumed Vascular Origin

Objectives: To assess the ability of 3D amide proton transfer weighted (APTw) imaging based on magnetization transfer analysis to discriminate between multiple sclerosis lesions (MSL) and white matter hyperintensities of presumed vascular origin (WMH) and to compare APTw signal intensity of healthy white matter (healthy WM) with APTw signal intensity of MSL and WHM. Materials and Methods: A total of 27 patients (16 female, 11 males, mean age 39.6 years) with multiple sclerosis, 35 patients (17 females, 18 males, mean age 66.6 years) with small vessel disease (SVD) and 20 healthy young volunteers (9 females, 11 males, mean age 29 years) were included in the MSL, the WMH, and the healthy WM group. MSL and WMH were segmented on fluid attenuated inversion recovery (FLAIR) images underlaid onto APTw images. Histogram parameters (mean, median, 10th, 25th, 75th, 90th percentile) were calculated. Mean APTw signal intensity values in healthy WM were defined by "Region of interest" (ROI) measurements. Wilcoxon rank sum tests and receiver operating characteristics (ROC) curve analyses of clustered data were applied. Results: All histogram parameters except the 75 and 90th percentile were significantly different between MSL and WMH (p = 0.018-p = 0.034). MSL presented with higher median values in all parameters. The histogram parameters offered only low diagnostic performance in discriminating between MSL and WMH. The 10th percentile yielded the highest diagnostic performance with an AUC of 0.6245 (95% CI: [0.532, 0.717]). Mean APTw signal intensity values of MSL were significantly higher than mean values of healthy WM (p = 0.005). The mean values of WMH did not differ significantly from the values of healthy WM (p = 0.345). Conclusions: We found significant differences in APTw signal intensity, based on straightforward magnetization transfer analysis, between MSL and WMH and between MSL and healthy WM. Low AUC values from ROC analyses, however, suggest that it may be challenging to determine type of lesion with APTw imaging. More advanced analysis of the APT CEST signal may be helpful for further differentiation of MSL and WMH.

Sex and Age Dependencies of Aqueductal Cerebrospinal Fluid Dynamics Parameters in Healthy Subjects

Objectives

To assess the influence of age and sex on 10 cerebrospinal fluid (CSF) flow dynamics parameters measured with an MR phase contrast (PC) sequence within the cerebral aqueduct at the level of the intercollicular sulcus.

Materials and Methods

128 healthy subjects (66 female subjects with a mean age of 52.9 years and 62 male subjects with a mean age of 51.8 years) with a normal Evans index, normal medial temporal atrophy (MTA) score, and without known disorders of the CSF circulation were included in the study. A PC MR sequence on a 3T MR scanner was used. Ten different flow parameters were analyzed using postprocessing software. Ordinal and linear regression models were calculated.

Results

The parameters stroke volume (sex: p < 0.001, age: p = 0.003), forward flow volume (sex: p < 0.001, age: p = 0.002), backward flow volume (sex: p < 0.001, age: p = 0.018), absolute stroke volume (sex: p < 0.001, age: p = 0.005), mean flux (sex: p < 0.001, age: p = 0.001), peak velocity (sex: p = 0.009, age: p = 0.0016), and peak pressure gradient (sex: p = 0.029, age: p = 0.028) are significantly influenced by sex and age. The parameters regurgitant fraction, stroke distance, and mean velocity are not significantly influenced by sex and age.

Conclusion

CSF flow dynamics parameters measured in the cerebral aqueduct are partly age and sex dependent. For establishment of reliable reference values for clinical use in future studies, the impact of sex and age should be considered and incorporated.

Amide Proton Transfer Contrast Distribution in Different Brain Regions in Young Healthy Subjects

Objectives

To define normal signal intensity values of amide proton transfer-weighted (APTw) magnetic resonance (MR) imaging in different brain regions.

Materials and Methods

Twenty healthy subjects (9 females, mean age 29 years, range 19 - 37 years) underwent MR imaging at 3 Tesla. 3D APTw (RF saturation B_1,rms = 2 μT, duration 2 s, 100% duty cycle) and 2D T2-weighted turbo spin echo (TSE) images were acquired. Postprocessing (image fusion, ROI measurements of APTw intensity values in 22 different brain regions) was performed and controlled by two independent neuroradiologists. Values were measured separately for each brain hemisphere. A subject was scanned both in prone and supine position to investigate differences between hemispheres. A mixed model on a 5% significance level was used to assess the effect of gender, brain region and side on APTw intensity values.

Results

Mean APTw intensity values in the hippocampus and amygdala varied between 1.13 and 1.57%, in the deep subcortical nuclei (putamen, globus pallidus, head of caudate nucleus, thalamus, red nucleus, substantia nigra) between 0.73 and 1.84%, in the frontal, occipital and parietal cortex between 0.56 and 1.03%; in the insular cortex between 1.11 and 1.15%, in the temporal cortex between 1.22 and 1.37%, in the frontal, occipital and parietal white matter between 0.32 and 0.54% and in the temporal white matter between 0.83 and 0.89%. APTw intensity values were significantly impacted both by brain region (p < 0.001) and by side (p < 0.001), whereby overall values on the left side were higher than on the right side (1.13 vs. 0.9%). Gender did not significantly impact APTw intensity values (p = 0.24). APTw intensity values between the left and the right side were partially reversed after changing the position of one subject from supine to prone.

Conclusion

We determined normal baseline APTw intensity values in different anatomical localizations in healthy subjects. APTw intensity values differed both between anatomical regions and between left and right brain hemisphere.

Safety of intrauterine devices in MRI

Objectives

The paucity of safety information on intrauterine devices (IUD) for magnetic resonance imaging (MRI) examinations is clinically relevant. The aim of this study is to evaluate the MRI safety of clinically used IUDs composed of copper/gold and stainless steel at 1.5T and 3.0T.

Materials and methods

We assessed and compared the displacement force, torque effects, presence of imaging artifacts and heating of IUDs composed of copper/gold (western IUDs) and stainless steel (China) on 1.5 and 3.0T MRI systems.

Results

Gold/Copper IUDs can show small deflection angles of 7° ± 7° in the worst-case field gradient of 40T/m (equivalent to magnetic force of 0.5 mN), while the stainless steel IUD experienced significant magnetic force and deflection (Force > 7.5 N; deflection angle 90° ± 1°). Manual rotation and suspension method show no torque effects on gold/copper IUDs but high torque effects were observed by manual rotation on the stainless steel IUD. Heating measurements showed a temperature increase (rescaled to a wbSAR of 4 W/kg) of 1.4°C at 1.5T / 3.4°C at 3.0 T (stainless steel IUD), 3.2°C at 1.5 T / 3.8°C at 3 T (copper/gold IUD), 3.3°C at 1.5 T / 4.8°C at 3 T (copper 1), 3.8°C at 1.5 T / 4.8°C at 3 T (copper 2). The visible imaging artifacts of the copper and gold IUDs at 3 T MRI reach a diameter of 4 mm ± 1 mm, while the stainless steel IUD resulted in artifacts measuring 200mm ± 10 mm when using gradient echo pulse sequences.

Conclusions

Standard IUDs (copper/gold) can be considered as conditional for MR safety at 1.5 T and 3.0 T, demonstrating at wbSAR up to 4W/kg and a magnetic field gradient of up to 40T/m with minimal imaging artifacts. The stainless steel IUD, however, induces unacceptable artifacts and is potentially harmful to patients during MRI due to high magnetic dislocation forces and torque (MR unsafe).

In-vivo evaluation of neuronal and glial changes in amyotrophic lateral sclerosis with diffusion tensor spectroscopy

Diffusion tensor spectroscopy (DTS) combines features of magnetic resonance spectroscopy and diffusion tensor imaging and permits evaluating cell-type specific properties of microstructure by probing the diffusion of intracellular metabolites. This exploratory study investigates for the first time microstructural changes in the neuronal and glial compartments of the brain of patients with amyotrophic lateral sclerosis (ALS) using DTS. To this end, the diffusion properties of the neuronal metabolite tNAA (N-acetylaspartate + N-acetylaspartylglutamate) and the predominantly glial metabolites tCr (creatine + phosphocreatine) and tCho (choline-containing compounds) were evaluated in the primary motor cortex of 24 ALS patients and 27 healthy controls. Significantly increased values in the diffusivities of all three metabolites were found in ALS patients relative to controls. Further analysis revealed more pronounced microstructural alterations in ALS patients with limb onset than with bulbar onset relative to controls. This observation may be related to the fact that the spectroscopic voxel was positioned in the part of the motor cortex where the motor functions of the limbs are represented. The higher diffusivities of tNAA may reflect neuronal damage and/or may be a consequence of mitochondrial dysfunction in ALS. Increased diffusivities of tCr and tCho are in line with reactive microglia and astrocytes surrounding degenerating motor neurons in the primary motor cortex of ALS patients. This pilot study demonstrates for the first time that cell-type specific microstructural alterations in the brain of ALS patients may be explored in vivo and non-invasively with DTS. In conjunction with other microstructural magnetic resonance imaging techniques, DTS may provide further insights into the pathogenic mechanisms that underlie neurodegeneration in ALS.

Would it be safe to have a dog in the MRI scanner before your own examination? A multicenter study to establish hygiene facts related to dogs and men

OBJECTIVES

To determine whether it would be hygienic to evaluate dogs and humans in the same MRI scanner.

METHODS

We compared the bacterial load in colony-forming units (CFU) of human-pathogenic microorganisms in specimens taken from 18 men and 30 dogs. In addition, we compared the extent of bacterial contamination of an MRI scanner shared by dogs and humans with two other MRI scanners used exclusively by humans.

RESULTS

Our study shows a significantly higher bacterial load in specimens taken from men's beards compared with dogs' fur (p = 0.036). All of the men (18/18) showed high microbial counts, whereas only 23/30 dogs had high microbial counts and 7 dogs moderate microbial counts. Furthermore, human-pathogenic microorganisms were more frequently found in human beards (7/18) than in dog fur (4/30), although this difference did not reach statistical significance (p = 0.074). More microbes were found in human oral cavities than in dog oral cavities (p < 0.001). After MRI of dogs, routine scanner disinfection was undertaken and the CFU found in specimens isolated from the MRI scanning table and receiver coils showed significantly lower bacteria count compared with "human" MRI scanners (p < 0.05).

CONCLUSION

Our study shows that bearded men harbour significantly higher burden of microbes and more human-pathogenic strains than dogs. As the MRI scanner used for both dogs and humans was routinely cleaned after animal scanning, there was substantially lower bacterial load compared with scanners used exclusively for humans.

KEY POINTS

• Bearded men harbour significantly more microbes than dogs. • Dogs are no risk to humans if they use the same MRI. • Deficits in hospital hygiene are a relevant risk for patients.

Diffusion-Weighted Zonal Oblique Multislice-EPI Enhances the Detection of Small Lesions with Diffusion Restriction in the Brain Stem and Hippocampus: A Clinical Report of Selected Cases

Diffusion restriction is the morphologic hallmark of acute ischemic infarcts and excitotoxic brain injury in various cerebral pathologies. Diffusion restriction is visible as hyperintensity on DWI and as hypointensity on ADC maps. Due to the vicinity of multiple anatomic structures in the brain stem and hippocampus, very small lesions with diffusion restriction may result in severe clinical symptomatology, but these small lesions easily go undetected on standard cerebral DWI due to insufficient spatial resolution, T2* blurring, and image artifacts caused by susceptibility-related image distortions. Diffusion-weighted zonal oblique multislice-EPI with reduced FOV acquisition permits a considerable increase in spatial resolution and enhances the visualization of very small pathologic lesions in the brain stem and hippocampus. Improved performance in the depiction of different pathologic lesions with diffusion restriction in the brain stem and hippocampus using this sequence compared with standard DWI in selected cases is presented.

Texture analysis of apparent diffusion coefficient maps for treatment response assessment in prostate cancer bone metastases-A pilot study

OBJECTIVE

To evaluate whole-lesion volumetric texture analysis of apparent diffusion coefficient (ADC) maps for assessing treatment response in prostate cancer bone metastases.

MATERIALS AND METHODS

Texture analysis is performed in 12 treatment-naïve patients with 34 metastases before treatment and at one, two, and three months after the initiation of androgen deprivation therapy. Four first-order and 19 second-order statistical texture features are computed on the ADC maps in each lesion at every time point. Repeatability, inter-patient variability, and changes in the feature values under therapy are investigated. Spearman rank's correlation coefficients are calculated across time to demonstrate the relationship between the texture features and the serum prostate specific antigen (PSA) levels.

RESULTS

With few exceptions, the texture features exhibited moderate to high precision. At the same time, Friedman's tests revealed that all first-order and second-order statistical texture features changed significantly in response to therapy. Thereby, the majority of texture features showed significant changes in their values at all post-treatment time points relative to baseline. Bivariate analysis detected significant correlations between the great majority of texture features and the serum PSA levels. Thereby, three first-order and six second-order statistical features showed strong correlations with the serum PSA levels across time.

CONCLUSION

The findings in the present work indicate that whole-tumor volumetric texture analysis may be utilized for response assessment in prostate cancer bone metastases. The approach may be used as a complementary measure for treatment monitoring in conjunction with averaged ADC values.

Fully navigated 3 T proton magnetic resonance spectroscopy of liver metastases with inner-volume saturation

PURPOSE

To demonstrate that fully navigated magnetic resonance spectroscopy (MRS) with inner-volume saturation (IVS) at 3 T results in high-quality spectra that permit evaluating metabolic changes in hepatic metastases without the need for patient compliance.

METHODS

Nine patients with untreated, biopsy-proven large hepatic metastases (minimum diameter of 3 cm) were included. In each patient, localized proton MRS was performed in the metastatic lesion and in uninvolved liver parenchyma. To improve quality and consistency of proton MRS, navigator gating was thereby performed not only during acquisition of the spectroscopic data but also during localization imaging and throughout the preparation phases. IVS was utilized to reduce chemical shift displacement between different metabolites and to diminish flow artifacts. Metabolite quantities were normalized relative to the unsuppressed water peak and choline-containing compounds (CCC) to lipid ratios were determined. Wilcoxon signed-rank tests were used to assess differences in the amounts of lipids and CCC as well as the CCC-to-lipid ratios between liver metastases and normal-appearing liver parenchyma.

RESULTS

Fully navigated point-resolved spectroscopy with IVS resulted in high-quality spectra in all patients. Navigator gating during localization imaging and spectroscopic acquisition thereby ensured a precise localization of the spectroscopic voxel. Decreased quantities of lipid and CCC were observed in metastatic tissue compared with uninvolved liver parenchyma. However, the latter trend fell short of statistical significance. Moreover, elevated levels of the CCC-to-lipid ratios were detected in metastatic tissue relative to normal-appearing liver parenchyma.

CONCLUSIONS

The present study demonstrates that fully navigated MRS of the liver with IVS at 3 T allows for a precise localization of the spectroscopic voxel and results in high-quality spectra that permit evaluating liver metabolism without the need for patient compliance.

Non-Mono-Exponential Analysis of Diffusion-Weighted Imaging for Treatment Monitoring in Prostate Cancer Bone Metastases

Diffusion-weighted imaging quantified using the mono-exponential model has shown great promise for monitoring treatment response in prostate cancer bone metastases. The aim of this prospective study is to evaluate whether non-mono-exponential diffusion models better describe the water diffusion properties and may improve treatment response assessment. Diffusion-weighted imaging data of 12 treatment-naïve patients with 34 metastases acquired before and at one, two, and three months after initiation of antiandrogen treatment are analysed using the mono-exponential, the intravoxel incoherent motion, the stretched exponential, and the statistical model. Repeatability of the fitted parameters and changes under therapy are quantified. Model preference is assessed and correlation coefficients across times are calculated to delineate the relationship between the prostate-specific antigen levels and the diffusion parameters as well as between the diffusion parameters within each model. There is a clear preference for non-mono-exponential diffusion models at all time points. Particularly the stretched exponential is favoured in approximately 60% of the lesions. Its parameters increase significantly in response to treatment and are highly repeatable. Thus, the stretched exponential may be utilized as a potential optimal model for monitoring treatment response. Compared with the mono-exponential model, it may provide complementary information on tissue properties and improve response assessment.

Image denoising substantially improves accuracy and precision of intravoxel incoherent motion parameter estimates

Applicability of intravoxel incoherent motion (IVIM) imaging in the clinical setting is hampered by the limited reliability in particular of the perfusion-related parameter estimates. To alleviate this problem, various advanced postprocessing methods have been introduced. However, the underlying algorithms are not readily available and generally suffer from an increased computational burden. Contrary, several computationally fast image denoising methods have recently been proposed which are accessible online and may improve reliability of IVIM parameter estimates. The objective of the present work is to investigate the impact of image denoising on accuracy and precision of IVIM parameter estimates using comprehensive in-silico and in-vivo experiments. Image denoising is performed with four different algorithms that work on magnitude data: two algorithms which are based on nonlocal means (NLM) filtering, one algorithm that relies on local principal component analysis (LPCA) of the diffusion-weighted images, and another algorithms that exploits joint rank and edge constraints (JREC). Accuracy and precision of IVIM parameter estimates is investigated in an in-silico brain phantom and an in-vivo ground truth as a function of the signal-to-noise ratio for spatially homogenous and inhomogenous levels of Rician noise. Moreover, precision is evaluated using bootstrap analysis of in-vivo measurements. In the experiments, IVIM parameters are computed a) by using a segmented fit method and b) by performing a biexponential fit of the entire attenuation curve based on nonlinear least squares estimates. Irrespective of the fit method, the results demonstrate that reliability of IVIM parameter estimates is substantially improved by image denoising. The experiments show that the LPCA and the JREC algorithms perform in a similar manner and outperform the NLM-related methods. Relative to noisy data, accuracy of the IVIM parameters in the in-silico phantom improves after image denoising by 76–79%, 79–81%, 84–99% and precision by 74–80%, 80–83%, 84–95% for the perfusion fraction, the diffusion coefficient, and the pseudodiffusion coefficient, respectively, when the segmented fit method is used. Beyond that, the simulations reveal that denoising performance is not impeded by spatially inhomogeneous levels of Rician noise in the image. Since all investigated algorithms are freely available and work on magnitude data they can be readily applied in the clinical setting which may foster transition of IVIM imaging into clinical practice.

Reduction in respiratory motion artefacts on gadoxetate-enhanced MRI after training technicians to apply a simple and more patient-adapted breathing command

OBJECTIVE

To investigate whether a trained group of technicians using a modified breathing command during gadoxetate-enhanced liver MRI reduces respiratory motion artefacts compared to non-trained technicians using a traditional breathing command.

MATERIALS AND METHODS

The gadoxetate-enhanced liver MR images of 30 patients acquired using the traditional breathing command and the subsequent 30 patients after training the technicians to use a modified breathing command were analyzed. A subgroup of patients (n = 8) underwent scans both by trained and untrained technicians. Images obtained using the traditional and modified breathing command were compared for the presence of breathing artefacts [respiratory artefact-based image quality scores from 1 (best) to 5 (non-diagnostic)].

RESULTS

There was a highly significant improvement in the arterial phase image quality scores in patients using the modified breathing command compared to the traditional one (P < 0.001). The percentage of patients with severe and extensive breathing artefacts in the arterial phase decreased from 33.3 % to 6.7 % after introducing the modified breathing command (P = 0.021). In the subgroup that underwent MRI using both breathing commands, arterial phase image quality improved significantly (P = 0.008) using the modified breathing command.

CONCLUSION

Training technicians to use a modified breathing command significantly improved arterial phase image quality of gadoxetate-enhanced liver MRI.

KEY POINTS

• A modified breathing command reduced respiratory artefacts on arterial-phase gadoxetate-enhanced MRI (P < 0.001). • The modified command decreased severe and extensive arterial-phase breathing artefacts (P = 0.021). • Training technicians to use a modified breathing command improved arterial-phase images.

Pilot study on the detection of antiandrogen resistance using serial diffusion-weighted imaging of bone metastases in prostate cancer

PURPOSE

To evaluate serial apparent diffusion coefficient (ADC) measurements of bone metastases in prostate cancer to determine whether antiandrogen resistance can be detected and time to progression estimated.

MATERIALS AND METHODS

Diffusion-weighted imaging (DWI) was performed at 1.5T in nine patients with treatment-naïve metastatic prostate cancer (20 lesions) before antiandrogen treatment, after 1, 2, and 3 months of treatment, and thereafter every 4 months over 31 months or until antiandrogen resistance was detected. Tumor volumes were stable over time. Time courses of the ADCs when averaged over entire lesions and on functional diffusion maps (fDMs) were analyzed using marginal linear model (MLM) analysis.

RESULTS

Starting at 1 month, MLM analysis revealed decreasing mean ADCs (P = 0.001) over time. Simultaneously, the percentage of voxels with significantly higher ADCs decreased (P = 0.004), whereas the percentage of voxels with significantly lower ADCs increased (P < 0.001) on fDMs. Both mean ADCs (P = 0.042) and percentages of voxels with significantly higher ADCs on fDMs (P = 0.039) decreased more rapidly over time in patients with a shorter progression-free interval (PFI). Likewise, higher (P = 0.001) and more rapidly increasing (P = 0.002) percentages of voxels with significantly lower ADCs on fDMs were associated with a shorter PFI.

CONCLUSION

The results of our pilot study suggest that the evolution of ADCs over time may permit early identification of antiandrogen resistance in bone metastases. J. Magn. Reson. Imaging 2016;43:1407-1416.

Early treatment response in non-small cell lung cancer patients using diffusion-weighted imaging and functional diffusion maps--a feasibility study

OBJECTIVE

The aim of this study was to prospectively evaluate the feasibility of monitoring treatment response to chemotherapy in patients with non-small cell lung carcinoma using functional diffusion maps (fDMs).

MATERIALS AND METHODS

This study was approved by the Cantonal Research Ethics Committee and informed written consent was obtained from all patients. Nine patients (mean age = 66 years; range = 53-76 years, 5 females, 4 males) with overall 13 lesions were included. Imaging was performed within two weeks before initiation of chemotherapy and at one, two, and six weeks after initiation of chemotherapy. Imaging included a respiratory-triggered diffusion-weighted sequence including three b-factors (100, 600, and 800 s/mm2). Treatment response was defined by change in tumor diameter on computed tomography (CT) after two cycles of chemotherapy. Changes in the apparent diffusion coefficient (ADC) on a per-lesion basis and the percentages of voxel with significantly increased or decreased ADCs on fDMs were analyzed using repeated measures analysis of variance (ANOVA). Changes in tumor size were used as covariate to examine the ability of ADCs and fDM parameters to predict treatment response.

RESULTS

Repeated measures ANOVA revealed that the percentage of voxels with increased ADCs on fDMs (p = 0.002) as well as the mean ADC increase (p = 0.011) were significantly higher in good responders with a large reduction in tumor size on CT.

CONCLUSION

Our results indicate that the percentage of voxels with significantly increased ADCs on fDMs seems to be a promising biomarker for early prediction of treatment response in patients with non-small cell lung carcinoma. Contrary to averaged values, this approach allows the spatial heterogeneity of treatment response to be resolved.

Suction against resistance: a new breathing technique to significantly improve the blood flow ratio of the superior and inferior vena cava

OBJECTIVES

Optimal contrast within the pulmonary artery is achieved by the maximum amount of contrast-enhanced blood flowing through the superior vena cava (SVC), while minimum amounts of non-contrasted blood should originate from the inferior vena cava (IVC). This study aims to clarify whether "suction against resistance" might optimise this ratio.

METHODS

Phase-contrast pulse sequences on a 1.5T MRI magnet were used for flow quantification (mean flow (mL/s), stroke volume (Vol) in the SVC and IVC in volunteers. Different breathing manoeuvers were analysed repeatedly: free breathing; inspiration; expiration; suction against resistance, and Valsalva. To standardise breathing commands, volunteers performed suction and Valsalva manoeuvers with an MR-compatible manometer.

RESULTS

Suction against resistance was associated with a significant drop of the IVC/SVC flow quotient (1.63 [range 1.3-2.0] p < 0.05 at -10 mmHg and 1.48 [1.1-1.9] p < 0.01 at -20 mmHg) corresponding to increased blood flow from SVC and diminished flow originating from the IVC. The remaining breathing commands (free breathing 2.2; inspiration 2.4; expiration 2.4; Valsalva 10 mmHg 2.3; Valsalva 20 mmHg 2.6; and Valsalva 30 mmHg 2.2) showed no differences (p > 0.05).

CONCLUSIONS

Suction against resistance caused a significant drop in the IVC/SVC quotient. Theoretically, this breathing manoeuver might significantly improve the enhancement characteristics of CT angiography.

KEY POINTS

Suction provokes reduction in blood flow in the inferior vena cava. Ratio between the inferior and superior vena cava blood flow diminished during suction. Manometer used during breathing standardises MR phase-contrast blood flow measurements.

Displacement of malignant cells into the portal triad of the liver results in reduced liver perfusion, mimicking segmental Fatty liver

Liver steatosis is often observed in different clinical situations. Oncological patients undergoing systemic therapy often develop liver steatosis, which can be diagnosed with normal routine scans such as CT and ultrasound. In this case report, we show that an isolated infiltration of the portal triad with tumor cells could mimic a fatty-like infiltration of the liver. Radiologists and clinicians should be aware of this pitfall and should perform a biopsy in cases of doubt.

Differential diagnosis of Lemierre's syndrome in a patient with acute paresis of the abducens and oculomotor nerves

Lemierre's syndrome is characterized by anaerobic septicemia, internal jugular vein thrombosis, and septic emboli associated with infections of the head and neck. We describe an unusual and clinically confusing case of a young woman with an acute paresis of the abducens nerve and partial paresis of the right oculomotor nerve. After an extensive imaging diagnostic procedure, we also documented a peritonsillar abscess and various types of thromboses in intracranial and extracranial veins. Furthermore, we found brain and lung abscesses, which led us to establish the diagnosis of Lemierre's syndrome. Despite intensive anti-coagulation and antibiotic therapy, the patient developed a mycotic aneurysm in the right internal carotid artery directly adjacent to the previously thrombosed cavernous sinus. In summary, we were able to confirm that Lemierre's syndrome may occur in conjunction with uncharacteristic symptoms. Due to the sometimes confusing clinical symptoms as well as clinical and radiological specialties, we had to work on an interdisciplinary basis to minimize the delay prior to establishing the diagnosis and therapy.

Secondary malignant peritoneal mesothelioma of the greater omentum after therapy for primary pleural mesothelioma

Mesothelioma is the most common malignant primary tumor of the pleura and usually associated with inhalation of asbestos fibers. In contrast, peritoneal mesothelioma is a rare entity whose pathomechanism is not yet fully understood. The coexistence of pleural mesothelioma with secondary involvement of the abdominal cavity has not been addressed in the literature. In this case report, we describe secondary malignant mesothelioma of the greater omentum. A 69-year-old man with histologically proven pleural mesothelioma on the right side and no past medical history of asbestos exposure received palliative treatment consisting of a talc pleurodesis. After a 6-month interval of stable disease, a local progressive tumor of the right pleura was seen on a CT scan. Eleven months later, during follow-up, the patient presented at our emergency department with a sudden onset of diffuse abdominal pain. Abdominal ultrasound revealed a mass within the greater omentum and the coexistence of free fluid. Subsequent abdominal CT scans demonstrated tumor infiltration from the right pleura by a transdiaphragmatic route into the abdomen, where diffuse infiltration of the greater omentum was observed. Aspiration of the ascites and the biopsy of the greater omentum confirmed the diagnosis of secondary malignant mesothelioma of the peritoneum. In conclusion, we present the extremely rare diagnosis of secondary malignant mesothelioma of the abdomen, which arose as a result of local progression from the right pleura into the abdomen.

Insula-specific H magnetic resonance spectroscopy reactions in heavy smokers under acute nicotine withdrawal and after oral nicotine substitution

The aim of this study was to clarify whether addiction-specific neurometabolic reaction patterns occur in the insular cortex during acute nicotine withdrawal in tobacco smokers in comparison to nonsmokers. Fourteen male smokers and 10 male nonsmokers were included. Neurometabolites of the right and the left insular cortices were quantified by magnetic resonance spectroscopy (MRS) on a 3-Tesla scanner. Three separate MRS measurements were performed in each subject: among the smokers, the first measurement was done during normal smoking behavior, the second measurement during acute withdrawal (after 24 h of smoking abstinence), and the third shortly after administration of an oral nicotine substitute. Simultaneously, craving, withdrawal symptoms, and CO levels in exhaled air were determined during the three phases. The participants in the control group underwent the same MR protocol. In the smokers, during withdrawal, the insular cortex showed a significant increase in glutamine (Gln; p = 0.023) as well as a slight increase not reaching significance for glutamine/glutamate (Glx; p = 0.085) and a nonsignificant drop in myoinositol (mI; p = 0.381). These values tended to normalize after oral nicotine substitution treatment, even though differences were not significant: Gln (p = 0.225), Glx (p = 0.107) and mI (p = 0.810). Overall, the nonsmokers (control group) did not show any metabolic changes over all three phases (p > 0.05). In smokers, acute nicotine withdrawal produces a neurometabolic reaction pattern that is partly reversed by the administration of an oral nicotine substitute. The results are consistent with the expression of an addiction-specific neurometabolic shift in the brain and confirm the fact that the insular cortex seems to play a possible role in nicotine dependence.

Optimizing the functional diffusion map using Monte Carlo simulations

PURPOSE

To optimize the diagnostic accuracy of the functional diffusion map for monitoring tumor treatment response in cancer patients.

MATERIALS AND METHODS

Using Monte Carlo simulations, measurement precision of the apparent diffusion coefficient (ADC), and particularly accuracy of threshold determination from healthy reference tissue, are evaluated by investigating the repeatability limit of the ADC as a function of different degrees of diffusion weighting of the sequence. Phantom and in-vivo experiments are performed to verify and illustrate the results of the simulations.

RESULTS

While diagnostic accuracy of the functional diffusion map is hardly diminished by differing values of the T(2) relaxation time in tumor and reference tissue, it is shown to be impaired by differing ADCs, resulting in erroneously determined segmentation thresholds. This problem can be addressed by decreasing the maximum b-factor and increasing the number of signal averages at the maximum b-factor or, alternatively, the number of b-factors while favoring schemes with higher b-factors. Phantom experiments confirm the results of the simulations. In-vivo data are presented to illustrate the effect of sequence optimization on the diagnostic accuracy of the functional diffusion map.

CONCLUSION

The present work demonstrates that the diagnostic accuracy of the functional diffusion map can be impaired by inaccurate segmentation thresholds and derives means for its optimization that will increase the fidelity of future clinical studies.

Bone metastases from prostate cancer: assessing treatment response by using diffusion-weighted imaging and functional diffusion maps--initial observations

PURPOSE

To prospectively investigate and monitor the response to antiandrogen treatment of bone metastases in patients with prostate cancer by using diffusion-weighted (DW) magnetic resonance (MR) imaging with the apparent diffusion coefficient (ADC) and functional diffusion maps (DMs).

MATERIALS AND METHODS

This study had institutional review board approval; informed consent was obtained from all patients. Nine treatment-naive men (mean age, 73 years; range, 66-86 years) with 20 pelvic bone metastases were included. Imaging was performed before antiandrogen treatment and at 1, 2, and 3 months afterward. Imaging included a DW MR imaging sequence with five b factors (0-800 sec/mm²). Serum prostate-specific antigen (PSA) levels and mean ADCs of each metastasis were measured over time and analyzed by using the general linear model. Pairwise comparisons (paired-samples t tests) of PSA levels and ADCs before and after therapy were performed with the significance level set at P < .017 (Bonferroni correction). To determine the relationship between serum PSA level and the averaged mean ADCs in each patient, the two parameters were correlated across time. In addition, an analysis with functional DMs was performed to evaluate ADC response to treatment on a per-voxel basis.

RESULTS

Serum PSA levels decreased by more than 90% during therapy. The mean ADCs of metastases were increased significantly at 1 (P < .001), 2 (P = .002), and 3 (P = .011) months after therapy compared with pretreatment values. Heterogeneous response was revealed at functional DM analysis. After 1 month of therapy, 47.3% of all analyzed tumor voxels showed significantly increased ADCs, while 46.5% were unchanged and 6.2% exhibited decreased ADCs in comparison to the pretreatment values. At 3 months after therapy, the proportion of voxels showing ADC decrease was higher (13.7%) than that at 1 month.

CONCLUSION

DW MR imaging allows monitoring of antiandrogen therapy in bone metastases. PSA level decrease corresponded well with an increase in mean tumor ADC. Heterogeneity of tumor response to therapy was demonstrated by functional DM analysis.

High-resolution diffusion tensor imaging of prostate cancer using a reduced FOV technique

OBJECTIVE

Diffusion tensor imaging (DTI) offers the promise of improved tumor localization in prostate cancer but the technique suffers from susceptibility-induced artifacts that limit the achievable resolution. The present work employs a reduced field-of-view technique that enables high-resolution DTI of the prostate at 3T. Feasibility of the approach is demonstrated in a clinical study including 26 patients and 14 controls.

MATERIALS AND METHODS

Reduced field-of-view acquisition was established by non-coplanar application of the excitation and the refocusing pulse in conjunction with outer volume suppression. Accuracy for cancer detection of apparent diffusion coefficient (ADC) mapping and T2-weighted imaging was calculated and compared with reference to the findings of trans-rectal ultrasound-guided octant biopsy. Mean ADCs and fractional anisotropy (FA) values in the patients with positive and negative biopsies were compared to each other and to the controls.

RESULTS

Fine anatomical details were successfully depicted on the ADC maps with sub-millimeter resolution. Accuracy for prostate cancer detection was 73.5% for ADC maps and 71% for T2-weighted images, respectively. Cohen's kappa (κ=0.48) indicated moderate agreement of the two methods. The mean ADCs were significantly lower, the FA values higher, in the patients with positive biopsy than in the patients with negative biopsy and the controls. Monte Carlo simulations showed that the FA values, but not the ADCs, were slightly overestimated. Bootstrap analysis revealed that the ADC, but not the FA value, is a highly repeatable marker.

CONCLUSION

In conclusion, the present work introduces a new approach for high-resolution DTI of the prostate enabling a more accurate detection of focal tumors especially useful in screening populations or as a potential navigator for image-guided biopsy.

Three-dimensional alignment of the aggregated myocytes in the normal and hypertrophic murine heart

Several observations suggest that the transmission of myocardial forces is influenced in part by the spatial arrangement of the myocytes aggregated together within ventricular mass. Our aim was to assess, using diffusion tensor magnetic resonance imaging (DT-MRI), any differences in the three-dimensional arrangement of these myocytes in the normal heart compared with the hypertrophic murine myocardium. We induced ventricular hypertrophy in seven mice by infusion of angiotensin II through a subcutaneous pump, with seven other mice serving as controls. DT-MRI of explanted hearts was performed at 3.0 Tesla. We used the primary eigenvector in each voxel to determine the three-dimensional orientation of aggregated myocytes in respect to their helical angles and their transmural courses (intruding angles). Compared with controls, the hypertrophic hearts showed significant increases in myocardial mass and the outer radius of the left ventricular chamber ( P < 0.05). In both groups, a significant change was noted from positive intruding angles at the base to negative angles at the ventricular apex ( P < 0.01). Compared with controls, the hypertrophied hearts had significantly larger intruding angles of the aggregated myocytes, notably in the apical and basal slices ( P < 0.001). In both groups, the helical angles were greatest in midventricular sections, albeit with significantly smaller angles in the mice with hypertrophied myocardium ( P < 0.01). The use of DT-MRI revealed significant differences in helix and intruding angles of the myocytes in the mice with hypertrophied myocardium.

Construction of a temperature-controlled diffusion phantom for quality control of diffusion measurements

PURPOSE

To construct a temperature-controlled diffusion phantom with known diffusion properties and geometry in order to facilitate the comparison and optimization of diffusion sequences with the objective of increasing the precision of experimentally derived diffusion parameters.

MATERIALS AND METHODS

A temperature-stabilized diffusion phantom made up of two crossing strands of hydrophobic polyethylene fibers was constructed. Reproducibility and temperature dependence of several diffusion parameters was investigated and compared with computer simulations. Furthermore, in order to stimulate actual use, the precision of measurement of different diffusion-encoding schemes was compared using bootstrap analysis.

RESULTS

The measured values of the diffusion parameters are highly reproducible and feature strong temperature dependence which is reproduced in simulations, underlining the necessity of a temperature-stabilized environment for quality control. The exemplary application presented here demonstrates that the phantom allows comparing and optimizing different diffusion sequences with regard to their measurement precision.

CONCLUSION

The present work demonstrates that the diffusion phantom facilitates and improves the comparison and quality control of diffusion sequences and the ensuing parameters. The results show that an accurate temperature control is a vital prerequisite for highly reproducible calibration measurements. As such, the phantom might provide a valuable calibration tool for clinical studies.

Reconstruction of the human visual system based on DTI fiber tracking

PURPOSE

To apply and to evaluate the newly developed advanced fast marching algorithm (aFM) in vivo by reconstructing the human visual pathway, which is characterized by areas of extensive fiber crossing and branching, i.e., the optic chiasm and the lateral geniculate nucleus (LGN).

MATERIALS AND METHODS

Diffusion tensor images were acquired in 10 healthy volunteers. Due to the proximity to bony structures and air-filled spaces of the optic chiasm, a high sensitivity encoding (SENSE) reduction factor was applied to reduce image distortions in this area. To reconstruct the visual system, three different seed areas were chosen separately. The results obtained by the aFM tracking algorithm were compared and validated with known anatomy.

RESULTS

The visual system could be reconstructed reproducibly in all subjects and the reconstructed fiber pathways are in good agreement with known anatomy.

CONCLUSION

The present work shows that the advanced aFM, which is especially designed for overcoming tracking limitations within areas of extensive fiber crossing, handles the fiber crossing and branching within the optic chiasm and the LGN correctly, thus allowing the reconstruction of the entire human visual fiber pathway, from the intraorbital segment of the optic nerves to the visual cortex.