Angel Alberich-Bayarri

Use of 3.0-T MR imaging for evaluation of the abdomen.

The most important advantage of 3.0-T magnetic resonance (MR) imaging systems is their increased signal-to-noise ratio (SNR) compared with 1.5-T systems. The higher SNR can be used to shorten acquisition time, achieve higher spatial resolution, or a combination of the two, thereby improving image quality and clinical diagnosis. In fact, 3.0-T MR imaging systems have already proved superior to 1.5-T systems in neuroradiologic and musculoskeletal applications. In the abdomen, 3.0-T MR imaging is uniquely beneficial for techniques such as enhanced and nonenhanced hepatic imaging, diffusion-weighted imaging, angiography, MR pancreatography, and colonography. Admittedly, 3.0-T abdominal imaging has important technical limitations, such as standing wave artifact, chemical shift artifact, susceptibility artifact, and safety issues such as increased energy deposition within the patients body. Furthermore, 3.0-T abdominal MR imaging is still in the early stages of development and requires substantial modifications of the pulse sequences and hardware components used for 1.5-T imaging. Nevertheless, the ability to obtain physiologic and functional information within reasonably short acquisition times with 3.0-T abdominal MR imaging bodies well for the future of this imaging technique.

Assessment of 2D and 3D fractal dimension measurements of trabecular bone from high-spatial resolution magnetic resonance images at 3 T.

PURPOSE In vivo two-dimensional (2D) fractal dimension (D2D) analysis of the cancellous bone at 1.5 T has been related to bone structural complexity and shown to be a potential imaging-based biomarker for osteoporosis. The objectives of this study were to assess at 3 T the in vivo feasibility of three-dimensional (3D) bone fractal dimension (D3D) analysis, analyze the relationship of D2D and D3D with osteoporosis, and investigate the relationship of D3D with spinal bone mineral density (BMD). METHODS A total of 24 female subjects (67±7yr old, mean±SD) was included in this study. The cohort consisted of 12 healthy volunteers and 12 patients with osteoporosis. MR image acquisitions were performed in the nondominant metaphysis of the distal radius with a 3 T MR scanner and an isotropic resolution of 180μm. After segmentation and structural reconstruction, 2D and 3D box-counting algorithms were applied to calculate the fractal complexity of the cancellous bone. D2D and D3D values were compared between patients with osteoporosis and healthy subjects, and their relationship with radius BV/TV and spinal BMD was also assessed. RESULTS Significant differences between healthy subjects and patients with osteoporosis were obtained forD3D (p<0.001), with less differentiation for D2D (p=0.04). The relationship between fractal dimension and BMD was not significant (r=0.43, p=0.16 and r=0.23, p=0.48, for D2D and D3D, respectively). CONCLUSIONS The feasibility of trabecular boneD3D calculations at 3 T and the relationship of both D2D and D3D parameters with osteoporosis were demonstrated, with a better differentiation for the 3D method. Furthermore, the D3D parameter has probably a different nature of information regarding the trabecular bone status not directly explained by BMD alone. Future studies with subjects with osteopenia and larger sample sizes are warranted to further establish the potential of D2D and D3D in the study of osteoporosis.

In Vivo Trabecular Bone Morphologic and Mechanical Relationship Using High-Resolution 3-T MRI

OBJECTIVE The purpose of this study was to investigate the in vivo morphologic and elastic parameters of trabecular bone with high-resolution 3-T MRI in a healthy reference population. SUBJECTS AND METHODS A series of wrist MR images were acquired with high-spatial-resolution (180 mum) isotropic voxels from 40 subjects without reported bone disease. After image postprocessing, the bone volume-to-total volume ratio, trabecular thickness, trabecular separation, and trabecular number were calculated in the morphologic analysis. Trabecular bone was mechanically simulated using the finite-element method to calculate the apparent elastic modulus parameter. The relationship between morphologic and mechanical parameters was studied. The influence of the analyzed bone volume was also investigated. RESULTS Statistically significant sex influences were found on the bone volume-to-total volume ratio (p = 0.003), trabecular thickness (p = 0.02), and apparent elastic modulus (p = 0.01); these parameters were lower in women. However, trends were found only on trabecular separation (p = 0.06) and trabecular number (p = 0.07). Age had no statistically significant influence in any morphologic (bone volume-to-total volume ratio, r = -0.24, p = 0.13; trabecular thickness, r = -0.03, p = 0.88; trabecular separation, r = 0.12, p = 0.47; and trabecular number, r = -0.23, p = 0.16) or elastic (apparent elastic modulus, r = -0.18, p = 0.26) parameter. A statistically significant relationship between apparent elastic modulus and the square of bone volume-to-total volume ratio was found (r = 0.968, p < 0.001). This association was not seen (r = 0.185, p = 0.25) and apparent elastic modulus results were considerably different (p < 0.001) if the volume of analyzed bone was reduced. CONCLUSION We found that bone volume-to-total volume ratio, trabecular thickness, and apparent elastic modulus are parameters significantly influenced by sex. Apparent elastic modulus results show a relationship with bone volume-to-total volume ratio. Trabecular bone volume should be maximized for an appropriate mechanical analysis.

Automatic Individual Arterial Input Functions Calculated From PCA Outperform Manual and Population-Averaged Approaches for the Pharmacokinetic Modeling of DCE-MR Images

To introduce a segmentation method to calculate an automatic arterial input function (AIF) based on principal component analysis (PCA) of dynamic contrast enhanced MR (DCE‐MR) imaging and compare it with individual manually selected and population‐averaged AIFs using calculated pharmacokinetic parameters.

Overload hepatitides: quanti-qualitative analysis

Diffuse liver diseases have a definitive radiological importance due to the ability of MR imaging to demonstrate abnormalities before the patient is symptomatic or the liver damage is advanced. Biopsy procedures are invasive, may lead to complications and have a sample bias. Imaging biomarkers target to fat, water, and iron tissue concentrations may be considered as hepatic virtual biopsies. There is a need to identify a rapid and practicable method to accurately quantify liver steatosis, differentiate steatohepatitis from simple steatosis, grade the necroinflammatory activity, calculate the liver iron burden and monitor overload progression. MR is used in the evaluation of diffuse liver disorders with accurate approaches such as the use of chemical shift, Dixon vector analysis, turbo spin echo fat suppression, and T2* gradient echo techniques. These methods are influenced by some factors like proportional ambiguity, T1 and T2* effects on signal decay, adding a significant bias in the combined fat–water–iron quantification. A GRE multi-echo chemical shift sequence was configured to independently calculate fat, water, and iron parametric liver images. It is now necessary to conduct a pilot project in order to validate this method in a group of subjects without and with different grades of fat, water, and iron liver changes.

Pharmacokinetic MR analysis of the cartilage is influenced by field strength

PURPOSE To study if the pharmacokinetic parameters derived from dynamic contrast-enhanced magnetic resonance (DCE-MR) images of the patellar cartilage are influenced by the main magnetic field strength. MATERIALS AND METHODS DCE-MR images of the knee were obtained from 16 normal male subjects (eight cases in each 1.5 and 3T magnets). Also, four volunteers were evaluated in both equipments within 1 week. Cartilage pharmacokinetic parameters of vascular permeability (K(trans)), extraction ratio (k(ep)), extravascular extracellular space volume fraction (v(e)) and intravascular space volume fraction (v(p)) were obtained. RESULTS Statistically significant differences were observed between the 1.5 and 3T groups for K(trans) (mean+/-S.D.; 5.44+/-2.27 vs. 1.01+/-0.41, respectively) and v(e) (3.37+/-2.32 vs. 0.81+/-0.80). A difference in K(trans) was also present when the same controls were evaluated in both equipments. There were no significant differences for k(ep) and v(p) values. Reproducibility of the pharmacokinetic calculations, assessed with the 24 acquisitions, showed a very low test-retest root mean square coefficient of variation (0.13, 0.10, 0.23 and 0.18 for K(trans), k(ep), v(e) and v(p), respectively). CONCLUSION Cartilage vascular permeability values are influenced by the MR field strength. This should be taken in consideration when analyzing this biomarker.

Volume Mesh Generation and Finite Element Analysis of Trabecular Bone Magnetic Resonance Images

In order to help the assessment of trabecular bone diseases and complement dual X-Ray absorptiometry (DXA) in diagnosis process, it is needed an accurate mechanical characterization of trabecular bone structure to estimate the risk of fracture and evaluate micro-architecture deterioration. As Finite Element modeling has become a well-established method for analysis of complex structures, an algorithm has been developed to build a Finite Element mesh from three-dimensional reconstruction information in voxels. Generated mesh is loaded in a finite element analysis software in order to simulate micro-architecture mechanical behavior under compression conditions. Most part of related researches have been based on ex vivo micro-computed tomography (muCT) scans. This study uses three-dimensional trabecular bone reconstructions from high resolution magnetic resonance images acquired in vivo.

Tissue iron quantification in chronic liver diseases using MRI shows a relationship between iron accumulation in liver, spleen, and bone marrow

AIM To investigate iron loading within the liver, pancreas, spleen, and bone marrow using magnetic resonance imaging (MRI) transverse relaxation rate (R2*), in patients with diffuse liver diseases; to evaluate the relationships between iron accumulation in these tissue compartments; and to assess the association between tissue iron overload and the pattern of hepatic cellular iron distribution (hepatocytes versus Kupffer cells). MATERIAL AND METHODS Fifty-six patients with diffuse liver diseases had MRI-derived R2* values, using a multi-echo chemical-shift encoded MRI sequence, of the liver, pancreas, spleen, and vertebral bone marrow. All patients had liver biopsy samples scored for hepatic iron grading (0-4) and iron cellular distribution (within hepatocytes only or within both hepatocytes and Kupffer cells). RESULTS Liver R2* increased with histological iron grade (RS=0.58, p<0.001) and correlated with spleen (RS=0.71, p<0.001) and bone marrow R2* (RS=0.66, p<0.001), but not with pancreatic R2* (RS=0.22, p=0.096). Splenic and bone marrow R2* values were also correlated (RS=0.72, p<0.001). Patients with iron inside Kupffer cells had the highest R2* in liver, spleen and bone marrow. CONCLUSIONS Patients with chronic diffuse liver diseases have concomitant hepatic, splenic, and bone marrow iron loading. The highest hepatic iron scores and iron inside Kupffer cells were associated with the highest splenic and bone marrow deposits, suggesting systemic iron accumulation in the mononuclear phagocytic system.

State-of-the-art of bone marrow imaging in multiple myeloma.

Purpose of review Multiple myeloma is a common hematological malignancy arising in the bone marrow. Bone lesions were initially depicted with conventional radiography, although recently 18F-FDG PET/CT and MRI are recognized as having a clear role in the initial workup and in the evaluation of therapy response. Recent findings Tumor development produces osteolysis and expansive lesions. Although tumor burden and extent are key prognostic factors, different cancer hallmarks can also be evaluated in vivo through noninvasive imaging. Summary This imaging-based virtual biopsy approach might be useful to define several relevant prognostic markers, such as angiogenesis, cellularity, metabolic trapping and bone morphology and elasticity, both before and during treatment, to predict tumor behavior and the early effect of therapy.

Imaging biomarkers processing platform

This paper presents the preliminary work in a software tool to provide the service of imaging biomarkers quantification for radiologists, supporting a wide variety of biomarkers for several types of acquired images, mainly focused on computed tomography (CT), magnetic resonance (MR) and derived image types. The platform can be accessed from every hospital in a shared network, allowing radiologists to upload medical images or select them from the picture archiving and communication system (PACS), and choose the appropriate imaging biomarker for the selected images. Once the images and the biomarker are correctly selected, the post-processing phase will be executed. Then, the platform sends a message to the system administrator in order to attend imaging processes whenever necessary, especially in semi-automatic workflows that need expert interaction. When the biomarker has been obtained, an automatic report is generated, offering several templates to the radiologist for the final report customization. Internally, the system takes care of saving the results on a local database and sending a copy of the report to the source PACS in DICOM Structured Report format. Nowadays, this platform has a collection of eighteen biomarkers that can be applied in several clinical research areas like neuroscience, cardiovascular, thorax, abdomen, pelvis, musculoskeletal or oncology.