X-ray-Based 3D Virtual Histology-Adding the Next Dimension to Histological Analysis.

Histology and immunohistochemistry of thin tissue sections have been the standard diagnostic procedure in many diseases for decades. This method is highly specific for particular tissue regions or cells, but mechanical sectioning of the specimens is required, which destroys the sample in the process and can lead to non-uniform tissue deformations. In addition, regions of interest cannot be located beforehand and the analysis is intrinsically two-dimensional. Micro X-ray computed tomography (µCT) on the other hand can provide 3D images at high resolution and allows for quantification of tissue structures, as well as the localization of small regions of interest. These advantages advocate the use of µCT for virtual histology tool with or without subsequent classical histology. This review summarizes the most recent examples of virtual histology and provides currently known possibilities of improving contrast and resolution of µCT. Following a background in µCT imaging, ex vivo staining procedures for contrast enhancement are presented as well as label-free virtual histology approaches and the technologies, which could rapidly advance it, such as phase-contrast CT. Novel approaches such as zoom tomography and nanoparticulate contrast agents will also be considered. The current evidence suggests that virtual histology may present a valuable addition to the workflow of histological analysis, potentially reducing the workload in pathology, refining tissue classification, and supporting the detection of small malignancies.

Combined use of two supervised learning algorithms to model sea turtle behaviours from tri-axial acceleration data.

Accelerometers are becoming ever more important sensors in animal-attached technology, providing data that allow determination of body posture and movement and thereby helping to elucidate behaviour in animals that are difficult to observe. We sought to validate the identification of sea turtle behaviours from accelerometer signals by deploying tags on the carapace of a juvenile loggerhead (Caretta caretta), an adult hawksbill (Eretmochelys imbricata) and an adult green turtle (Chelonia mydas) at Aquarium La Rochelle, France. We recorded tri-axial acceleration at 50 Hz for each species for a full day while two fixed cameras recorded their behaviours. We identified behaviours from the acceleration data using two different supervised learning algorithms, Random Forest and Classification And Regression Tree (CART), treating the data from the adult animals as separate from the juvenile data. We achieved a global accuracy of 81.30% for the adult hawksbill and green turtle CART model and 71.63% for the juvenile loggerhead, identifying 10 and 12 different behaviours, respectively. Equivalent figures were 86.96% for the adult hawksbill and green turtle Random Forest model and 79.49% for the juvenile loggerhead, for the same behaviours. The use of Random Forest combined with CART algorithms allowed us to understand the decision rules implicated in behaviour discrimination, and thus remove or group together some 'confused' or under--represented behaviours in order to get the most accurate models. This study is the first to validate accelerometer data to identify turtle behaviours and the approach can now be tested on other captive sea turtle species.

Computer vision tools to optimize reconstruction parameters in x-ray in-line phase tomography.

In this article, a set of three computer vision tools, including scale invariant feature transform (SIFT), a measure of focus, and a measure based on tractography are demonstrated to be useful in replacing the eye of the expert in the optimization of the reconstruction parameters in x-ray in-line phase tomography. We demonstrate how these computer vision tools can be used to inject priors on the shape and scale of the object to be reconstructed. This is illustrated with the Paganin single intensity image phase retrieval algorithm in heterogeneous soft tissues of biomedical interest, where the selection of the reconstruction parameters was previously made from visual inspection or physical assumptions on the composition of the sample.

Synchrotron radiation X-ray phase micro-computed tomography as a new method to detect iron oxide nanoparticles in the brain.

PURPOSE: The purpose of this study was to introduce synchrotron radiation X-ray phase computed tomography (SR-PCT) as a new method of visualizing ultrasmall superparamagnetic particles of iron oxide (USPIO) distribution into the brains of mice with neuroinflammation. PROCEDURES: The sensitivity of the technique was assessed by performing back-to-back SR-PCT and magnetic resonance imaging (MRI) in mice stereotaxically injected with a range of USPIO concentrations. Eight mice with cerebral ischemia were then intravenously injected with USPIOs and imaged back-to-back with MRI and SR-PCT. RESULTS: SR-PCT proved sensitive enough to detect iron in nanomolar quantities. In stroke-induced animals, SR-PCT showed hyperintense areas in the regions of MR signal loss and immunostaining for macrophages. SR-PCT, moreover, identified brain anatomy as clearly as histology, without the need for sectioning or staining, with an examination time of 44 min per brain at an isotropic spatial resolution of 8 µm. CONCLUSION: SR-PCT has potential for cellular imaging in intact brain, with unequaled neuroanatomy.

Imaging inflammation in stroke using magnetic resonance imaging.

Stroke is the third leading cause of death, after myocardial infarction and cancer, and the leading cause of permanent disability in Western countries. Although anti-inflammatory drugs have shown very promising results in preclinical rodent studies, they appeared to be ineffective against stroke in clinical trials. In this context, non-invasive detection of inflammatory cells after brain ischemia could be helpful (i) to select patients who may benefit from anti-inflammatory treatment, and/or (ii) to target an adequate individualized therapeutic time window. Magnetic resonance imaging (MRI) coupled with injection of iron oxide nanoparticles, a contrast agent taken up by macrophages ex vivo and in vivo, appears to be a promising tool for this purpose. This review focuses on the use of this technique to image inflammation in pre-clinical and clinical studies of stroke. Despite current limitations, MRI of inflammation may become an important tool for the investigation of novel ischemic stroke therapeutics targeting inflammation.

Quantitative effects of cell internalization of two types of ultrasmall superparamagnetic iron oxide nanoparticles at 4.7 T and 7 T.

PURPOSE: MRI coupled with the intravenous injection of ultrasmall superparamagnetic particles of iron oxides (USPIOs) is a promising tool for the study of neuroinflammation. Quantification of the approximate number of magnetically labelled macrophages may provide an effective and efficient method for monitoring inflammatory cells. The purpose of the present study was to characterise the relaxation properties of macrophages labelled with two types of USPIOs, at 4.7 T and 7 T. METHODS: USPIO-labelled bone-marrow-derived macrophage phantoms were compared with phantoms of free dispersed USPIOs with the same global iron concentration, using multi-parametric (T1, T2 and T2) quantitative MRI. The same protocol was then evaluated in living mice after intracerebral injection of iron-labelled macrophages vs free iron oxide. RESULTS: A linear relationship was observed among R1, R2 and R2 values and iron concentration in vitro at 4.7 T and at 7 T. At a given field, T1 and T2 relaxivities of both types of USPIOs decreased following internalisation into macrophages, while T2 relaxivities increased. CONCLUSION: There was fair overall agreement between the theoretical number of injected cells and the number estimated from T2 quantification and in vitro calibration curves, supporting the validity of the present in vitro calibration curves for in vivo investigation.

Clinical and imaging predictors of intracerebral haemorrhage in stroke patients treated with intravenous tissue plasminogen activator.

OBJECTIVE: To evaluate clinical, biological, and pretreatment imaging variables for predictors of tissue plasminogen activator (tPA) related intracerebral haemorrhage (ICH) in stroke patients. METHODS: 48 consecutive patients with hemispheric stroke were given intravenous tPA within seven hours of symptom onset, after computed tomography (CT) and magnetic resonance imaging (MRI) of the brain. Baseline diffusion weighted (DWI) and perfusion weighted (PWI) imaging volumes, time to peak, mean transit time, regional cerebral blood flow index, and regional cerebral blood volume were evaluated. The distribution of apparent diffusion coefficient (ADC) values was determined within each DWI lesion. RESULTS: The symptomatic ICH rate was 8.3% (four of 48); the rate for any ICH was 43.8% (21 of 48). Univariate analysis showed that age, weight, history of hyperlipidaemia, baseline NIHSS score, glucose level, red blood cell count, and lacunar state on MRI were associated with ICH. However, mean 24 hour systolic blood pressure and a hyperdense artery sign on pretreatment CT were the only independent predictors of ICH. Patients with a hyperdense artery sign had larger pretreatment PWI and DWI lesion volumes and a higher NIHSS score. Analysis of the distribution of ADC values within DWI lesions showed that a greater percentage of pixels had lower ADCs (< 400 x 10(-6) mm(2)/s) in patients who experienced ICH than in those who did not. CONCLUSION: Key clinical and biological variables, pretreatment CT signs, and MRI indices are associated with tPA related intracerebral haemorrhage.

Influence of the site of arterial occlusion on multiple baseline hemodynamic MRI parameters and post-thrombolytic recanalization in acute stroke.

In this prospective MRI study, we evaluated the impact of the site of occlusion on multiple baseline perfusion parameters and subsequent recanalization in 49 stroke patients who were given intravenous tissue plasminogen activator (tPA). Pretreatment magnetic resonance angiography (MRA) revealed an arterial occlusion in 47 patients: (1) internal carotid artery (ICA) + M1 middle cerebral artery (MCA) occlusion (n=12); (2) M1 MCA occlusion (n=19); (3) M2 MCA, distal branches of the MCA and anterior cerebral artery (ACA) occlusion (n=16). Patients with ICA occlusion had significantly larger DWI, PWI and mismatch lesion volume on pretreatment MRI compared to patients with other sites of occlusion. The differences in cerebral blood flow (CBF) and peak height were significantly higher in patients with ICA occlusion compared to patients with other sites of occlusion (P=0.03 and P=0.04, respectively). Day 1 MRA showed recanalization in 28 patients (60%). The rate of recanalization was significantly different depending on the site of occlusion: 33% in ICA + M1 MCA occlusion, 63% in M1 MCA occlusion and 81% in either M2 MCA, distal branches of the MCA or ACA occlusion (P=0.002). Our data suggest that CBF and peak height are the most relevant MRI parameters to assess the severity of hemodynamic impairment in regard to the site of occlusion.

The delayed perfusion sign at MRI.

PURPOSE: Effective collateral blood flow seem to be an important factor associated with a small infarct volume and a good clinical outcome. We aimed to assess leptomeningeal collateral blood flow on source perfusion-weighted images in patients with acute stroke. MATERIALS AND METHODS: 29 patients with proximal middle cerebral artery occlusion (MCA alone, n=17; MCA + internal carotid artery [ICA] occlusion, n=12) were evaluated with MRI at baseline before thrombolytic therapy, and at day 60. Clinical evaluation was performed at days 0 and 60 with the National Institutes of Health Stroke Scale (NIHSS) score, and at day 60 with the modified Rankin score. We assessed (on source images of the dynamic contrast-enhanced T2*-weighted perfusion [PWI] sequence) the presence of a hypointensity consistent with delayed contrast arrival within the global perfusion deficit (delayed perfusion sign). We analyzed the extent of the area demonstrating such delayed perfusion (DP area) on source images of the PWI sequence, and compared it with the global perfusion (GP) abnormality shown by time-to-peak maps. We calculated the Spearman rank correlation coefficient between the DP/GP ratio and: 1. age; 2. clinical scores; 3. site of occlusion [MCA alone versus ICA+MCA occlusion]; 4. DWI lesion size at day 0, and T2WI lesion size at day 60; 5. PWI-derived parameters (time-to-peak [TTP], relative cerebral blood volume [rCBV], relative cerebral blood flow [rCBF], and peak height). All tests were bilateral and a p value<0.05 was considered as significant. RESULTS: Delayed perfusion areas of various size were found within the global perfusion deficit in all patients. High DP/GP ratio values were significantly correlated with: 1. better clinical scores at day 0 and day 60 (all p<=0.04); 2. smaller lesions at day 0 DWI and at day 60 T2WI (all p<=0.004); 3. ICA patency (r=0.49, p=0.01); 4. lower TTP delays, and higher values of rCBV, rCBF, and peak height. CONCLUSION: These preliminary data suggest that a delayed contrast filling observed on native perfusion-weighted images may be a marker of leptomeningeal collateral blood flow, and may lead to better clinical and morphological outcomes in acute ischemic stroke.

CT pulmonary angiography with a macromolecular contrast medium: a comparative study versus iobitridol in rabbits.

RATIONALE AND OBJECTIVES: To compare the pharmacokinetics of a new macromolecular iodinated contrast medium, prototype P743, with a standard contrast agent (iobitridol) for spiral computed tomography pulmonary angiography in rabbits. METHODS: Manual injection was first used to test the performance of P743 even in cases of nonoptimal bolus timing. Then a protocol was designed to compare vessel enhancement in both first-pass and delayed scans for the two contrast agents with the help of a power injector. RESULTS: With manual fast injection, the first pass of iobitridol was observed only on proximal scans. Conversely, opacification of vessels was maintained during three spiral scans with P743 under the same injection conditions. When optimal bolus timing was performed, higher vessel enhancement was observed during bolus first pass with iobitridol (iodine dosage 250 mg I/kg) compared with P743 (150 mg I/kg). However, during the postbolus phase, the decrease in attenuation values was markedly faster with iobitridol than with P743. CONCLUSIONS: This study confirmed that P743 remains more intravascular than iobitridol, which may have clinical implications for the diagnosis of pulmonary embolism, for example.

Early diagnosis of hemorrhagic transformation: diffusion/perfusion-weighted MRI versus CT scan.

UNLABELLED: Standard magnetic resonance imaging (MRI) techniques failed to image adequately acute hemorrhagic transformation (HT). Therefore, computed tomography (CT) is still needed to exclude intracerebral hemorrhage. New MRI techniques such as diffusion- and perfusion-weighted imaging (DWI and PWI) may improve the early detection of HT. The utility of this approach requires a direct comparison of the sensitivity of CT with these MRI techniques. METHODS: Nine patients experienced an acute carotid artery territory ischemic stroke diagnosed on a first CT performed 3.8 +/- 2 h after the onset of stroke. They underwent a second CT 12 +/- 4 h after the onset of stroke, followed 35 +/- 10 min later by an MRI protocol including: (1) an axial isotropic DWI SE echo-planar imaging (EPI) sequence; (2) time of flight MR angiography (TOF MRA); (3) PWI with an axial T(2)*-weighted gradient echo EPI sequence using 20 ml gadolinium contrast agent (Gd-DTPA); HT was characterized on DWI SE EPI as a heterogeneous area of signal loss within the ischemic area; (4) at day 7, CT was also performed in all patients who had an early suspicion of bleeding according to MRI. RESULTS: An HT was detected exclusively with CT in 1 out of 9 patients, while an MRI pattern of HT was found in 6 out of 9 patients. In 5 of these 6 patients, the CT scan did not show an obvious pattern of HT. Day 7 CT confirmed HT in all patients who had early suspicion of bleeding according to DWI criteria. CONCLUSION: This study suggests that new MRI techniques may allow an early detection of HT, thus improving the management of stroke.

Perfusion-based segmentation of the human brain using similarity mapping.

In this work, a method for segmenting human brain MR scans on the basis of perfusion is described. This technique uses a measure of similarity between the time-intensity curves obtained with dynamic susceptibility contrast-enhanced MRI and a modeled curve of reference to isolate a tissue of interest, such as white or gray matter. The aim of this study was to validate the method by performing segmentation of white and gray matter in six controls. The relative regional blood volume gray-to-white matter ratio was used as a criterion to assess the quality of segmentation. On average, this ratio was 2.1 +/- 0.2, which is in good agreement with the literature, thus suggesting reliable segmentation. In the case of abnormal perfusion, time-intensity curves are different in shape than that of normal tissue. Therefore, this approach might allow the segmentation of pathological regions, and combined with an indicator-dilution analysis might offer new possibilities for characterizing a brain pathology. Magn Reson Med 45:261-268, 2001.

Laser-polarized (3)He as a probe for dynamic regional measurements of lung perfusion and ventilation using magnetic resonance imaging.

Magnetic resonance imaging (MRI) using laser-polarized noble gases, such as (129)Xe and (3)He, allows unparalleled noninvasive information on gas distribution in lung airways and distal spaces. In addition to pulmonary ventilation, lung perfusion assessment is crucial for proper diagnosis of pathological conditions, such as pulmonary embolism. Magnetic resonance perfusion imaging usually can be performed using techniques based on the detection of water protons in tissues. However, lung proton imaging is extremely difficult due to the low proton density and the magnetically inhomogeneous structure of the lung parenchyma. Here we show that laser-polarized (3)He can be used as a noninvasive probe to image, in a single MRI experiment, not only the ventilation but also the perfusion state of the lungs. Blood volume maps of the lungs were generated based on the (3)He signal depletion during the first pass of a superparamagnetic contrast agent bolus. The combined and simultaneous lung ventilation and perfusion assessments are demonstrated in normal rat lungs and are applied to an experimental animal model of pulmonary embolism. Magn Reson Med 44:1-4, 2000.

Vasodilatory response of border zones to acetazolamide before and after endarterectomy : an echo planar imaging-dynamic susceptibility contrast-enhanced MRI study in patients with high-grade unilateral internal carotid artery stenosis.

BACKGROUND AND PURPOSE: The importance of hemodynamic changes related to a high-grade internal carotid artery (ICA) stenosis remains a matter of controversy. Areas between the vascular territories of major cerebral arteries, namely, the border zones, may be selectively vulnerable to hemodynamic alteration. The aim of this study was to search for any hemodynamic impact of carotid endarterectomy (CEA) on vasodilatory response, in particular, within the border zones, by means of multislice dynamic susceptibility contrast MRI. METHODS: Thirteen patients with a high-grade unilateral ICA stenosis (>80%) were examined. Relative regional cerebral blood volume (rrCBV) was determined separately for white matter, gray matter, and anterior and posterior border zones by the acetazolamide test. A vasomotor reactivity index was evaluated from the rrCBV values. Values from the ipsilateral hemisphere were compared with contralateral ones, before and after CEA. RESULTS: Before CEA, rrCBV values in the anterior border zones were significantly (P<0.05) higher in the ipsilateral hemisphere than in the contralateral hemisphere. A decrease in vasomotor reactivity indexes was also observed in the lesion side, but the difference from the contralateral side was not statistically significant. In posterior border zones, no differences in rrCBV or vasomotor reactivity were found between the ipsilateral and the contralateral hemispheres. After CEA, the rrCBV asymmetry in the anterior border zones cleared. CONCLUSIONS: High-grade ICA stenosis with efficient primary collateral pathways may have an early limited hemodynamic impact within border-zone areas. The favorable course of these abnormalities after surgery suggests an additional benefit of CEA at this stage.

Effects of subcortical cerebrovascular lesions on cortical hemodynamic parameters assessed by perfusion magnetic resonance imaging.

A simultaneous decrease of cerebral blood volume (CBV) and cerebral blood flow (CBF) has been described after subcortical stroke with positron emission tomography. However, this imaging modality cannot be applied routinely to stroke patients. Dynamic susceptibility contrast-enhanced MRI techniques (DSC-MRI) might be interesting in the assessment of these effects. Dynamic T2-weighted echo planar imaging was used to produce DSC-MR images during an intravenous bolus injection of gadopentetate dimeglumine in 9 patients who experienced a subcortical stroke involving thalamus or basal ganglia and in 8 control subjects. A series of 50 consecutive images at 1-second intervals was acquired at the anatomic level of the centrum semiovale quite distant from the subcortical lesion, rCBF and rCBV were determined over frontal and parietal regions of interest and through the entire cortical mantle. DSC-MRI enabled the detection of hemodynamic changes induced by subcortical stroke. Analysis of rCBV and rCBF values showed that the hemodynamic parameters were significantly decreased on the affected side. In controls mean rCBF and rCBV values recorded over the whole cortical mantle of each hemisphere showed no significant interhemispheric asymmetry.

Prospective comparison of MR lung perfusion and lung scintigraphy.

This study attempted to assess the accuracy and potential of lung magnetic resonance (MR) perfusion imaging compared with perfusion scintigraphy in the evaluation of patients with suspected lung perfusion defects. The technique, which uses an inversion recovery turbo-FLASH sequence with ultra-short TE (1.4 msec), was tested in 24 patients suspected clinically of having acute pulmonary embolism (n = 19) and in patients with severe pulmonary emphysema (n = 5). Perfusion lung scintigraphy was performed within 48 hours prior to the MRI examination in both groups of patients. The dynamic study was acquired in the coronal plane and consisted of 10 images of 6 slices (a total of 60 images per series). Gadopentetate dimeglumine (0.1 mmol/kg) was manually injected as a compact bolus during the acquisition of the first image. Three senior radiologists reviewed all unprocessed two-dimensional coronal sections. They were blinded to clinical data and other imaging modalities. For the three observers, the average sensitivity and specificity of MR were 69% and 91%, respectively. The overall agreement between MR and scintigraphy appears to be good, with a good correlation between the two modalities (kappa = 0.63). However, the data showed variability depending on the location of the perfusion defect, with higher accuracy in the upper lobes. The agreement between MR perfusion and scintigraphy appears to be moderate in the left inferior lobe (kappa = 0.48). The data showed an overall good interobserver agreement (kappa = 0.66). MR perfusion of the lung is a promising technique in detecting lung perfusion defects.