Using a voxel-based krogh cylinder array to simulate microvascular contrast enhancement

The goal of this study is to better simulate microscopic and voxel-based dynamic contrast enhancement in magnetic resonance imaging. Specifically, errors imposed by the traditional two-compartment model are reduced by introducing a novel Krogh cylinder network. The two-compartment model was developed for macroscopic pharmacokinetic analysis of dynamic contrast enhancement and generalizing it to voxel dimensions, due to the significant decrease in scale, imposes physiologically unrealistic assumptions. In the project, a system of microscopic exchange between plasma and extravascular-extracellular space is built while numerically simulating the local contrast agent flow between and inside image elements. To do this, tissue parameter maps were created, contrast agent was introduced to the tissue via a flow lattice, and various data sets were simulated. The effects of sources, tissue heterogeneity, and the contribution of individual tissue parameters to an image are modeled. Further, the study attempts to demonstrate the effects of a priori flow maps on image contrast, indicating that flow data is as important as permeability data when analyzing tumor contrast enhancement. In addition, the simulations indicate that it may be possible to obtain tumor-type diagnostic information by acquiring both flow and permeability data.

Report to the director, National Center for Radiological Health, Public Health Service, on environmental contamination by radioactive substances, December 1, 1967.

Mode of access: Internet.

Radiological treatment of HCC: Interventional radiology at the heart of management

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Added value of diffusion-weighted MRI in detection of cervical cancer recurrence compared with morphologic and dynamic contrast-enhanced MRI sequences

PURPOSE We aimed to evaluate the added value of diffusion-weighted imaging (DWI) to standard magnetic resonance imaging (MRI) for detecting post-treatment cervical cancer recurrence. The detection accuracy of T2-weighted (T2W) images was compared with that of T2W MRI combined with either dynamic contrast-enhanced (DCE) MRI or DWI. METHODS Thirty-eight women with clinically suspected uterine cervical cancer recurrence more than six months after treatment completion were examined with 1.5 Tesla MRI including T2W, DCE, and DWI sequences. Disease was confirmed histologically and correlated with MRI findings. The diagnostic performance of T2W imaging and its combination with either DCE or DWI were analyzed. Sensitivity, positive predictive value, and accuracy were calculated. RESULTS Thirty-six women had histologically proven recurrence. The accuracy for recurrence detection was 80% with T2W/DCE MRI and 92.1% with T2W/DWI. The addition of DCE sequences did not significantly improve the diagnostic ability of T2W imaging, and this sequence combination misclassified two patients as falsely positive and seven as falsely negative. The T2W/DWI combination revealed a positive predictive value of 100% and only three false negatives. CONCLUSION The addition of DWI to T2W sequences considerably improved the diagnostic ability of MRI. Our results support the inclusion of DWI in the initial MRI protocol for the detection of cervical cancer recurrence, leaving DCE sequences as an option for uncertain cases.

A non-contrast self-navigated 3-dimensional MR technique for aortic root and vascular access route assessment in the context of transcatheter aortic valve replacement: proof of concept.

OBJECTIVES: Due to the high prevalence of renal failure in transcatheter aortic valve replacement (TAVR) candidates, a non-contrast MR technique is desirable for pre-procedural planning. We sought to evaluate the feasibility of a novel, non-contrast, free-breathing, self-navigated three-dimensional (SN3D) MR sequence for imaging the aorta from its root to the iliofemoral run-off in comparison to non-contrast two-dimensional-balanced steady-state free-precession (2D-bSSFP) imaging. METHODS: SN3D [field of view (FOV), 220-370 mm(3); slice thickness, 1.15 mm; repetition/echo time (TR/TE), 3.1/1.5 ms; and flip angle, 115°] and 2D-bSSFP acquisitions (FOV, 340 mm; slice thickness, 6 mm; TR/TE, 2.3/1.1 ms; flip angle, 77°) were performed in 10 healthy subjects (all male; mean age, 30.3 ± 4.3 yrs) using a 1.5-T MRI system. Aortic root measurements and qualitative image ratings (four-point Likert-scale) were compared. RESULTS: The mean effective aortic annulus diameter was similar for 2D-bSSFP and SN3D (26.7 ± 0.7 vs. 26.1 ± 0.9 mm, p = 0.23). The mean image quality of 2D-bSSFP (4; IQR 3-4) was rated slightly higher (p = 0.03) than SN3D (3; IQR 2-4). The mean total acquisition time for SN3D imaging was 12.8 ± 2.4 min. CONCLUSIONS: Our results suggest that a novel SN3D sequence allows rapid, free-breathing assessment of the aortic root and the aortoiliofemoral system without administration of contrast medium. KEY POINTS: • The prevalence of renal failure is high among TAVR candidates. • Non-contrast 3D MR angiography allows for TAVR procedure planning. • The self-navigated sequence provides a significantly reduced scanning time.

Contrast sensitivity evaluation with filter contact lenses in patients with retinitis pigmentosa: a pilot study

Purpose: the aim of this pilot study was to test whether retinitis pigmentosa patients would benefit from filter contact lenses as an effective optical aid against glare and photophobia. Methods: fifteen subjects with retinitis pigmentosa were enrolled in this study. All of them were evaluated with filter soft contact lenses (MaxSight), filter glasses (CPF 527) and without filters (control). All patients were assessed for the three aid conditions by means of best corrected visual acuity (BCVA), contrast sensitivity (without glare and with central and peripheral glare)(CSV-1000) and a specific subjective questionnaire about quality of vision. Results: BCVA was slightly better with filters than without filter but the differences were not statistically significant. Contrast sensitivity without glare improved significantly with the contact lenses (p<0.05). The central glare had significant differences for the frequencies of 3 cpd and 18 cpd between the contact lens filter and the control group (p=0.021 and p=0.044, respectively). For the peripheral glare contrast sensitivity improved with contact lens versus control group for highest frequencies, 12 and 18 cpd (p<0.001 and p=0.045, respectively). According to the questionnaire the contact lens filter gave them more visual comfort than the glasses filter under the scenarios of indoors glare, outdoors activities and indoors comfort. Conclusion: the filter contact lenses seem to be a good option to improve the quality of vision of patients with retinitis pigmentosa.

Cerebral misery perfusion diagnosed using hypercapnic blood-oxygenation-level-dependent contrast functional magnetic resonance imaging: a case report

Introduction Cerebral misery perfusion represents a failure of cerebral autoregulation. It is animportant differential diagnosis in post-stroke patients presenting with collapses in the presence of haemodynamically significant cerebrovascular stenosis. This is particularly the case when cortical or internal watershed infarcts are present. When this condition occurs, further investigation should be done immediately. Case presentation A 50-year-old Caucasian man presented with a stroke secondary to complete occlusion of his left internal carotid artery. He went on to suffer recurrent seizures. Neuroimaging demonstrated numerous new watershed-territory cerebral infarcts. No source of arterial thromboembolism was demonstrable. Hypercapnic blood-oxygenation-level-dependent-contrast functional magnetic resonance imaging was used to measure his cerebrovascular reserve capacity. The findings were suggestive of cerebral misery perfusion. Conclusions Blood-oxygenation-level-dependent-contrast functional magnetic resonance imaging allows the inference of cerebral misery perfusion. This procedure is cheaper and more readily available than positron emission tomography imaging, which is the current gold standard diagnostic test. The most evaluated treatment for cerebral misery perfusion is extracranial-intracranial bypass. Although previous trials of this have been unfavourable, the results of new studies involving extracranial-intracranial bypass in high-risk patients identified during cerebral perfusion imaging are awaited. Cerebral misery perfusion is an important and under-recognized condition in which emerging imaging and treatment modalities present the possibility of practical and evidence-based management in the near future. Physicians should thus be aware of this disorder and of recent developments in diagnostic tests that allow its detection.

Analysis of only 0-1 min clip or 1-4 min Clip for focal liver lesions during contrast-enhanced ultrasonography

Purpose: To evaluate the reliability of analysis of only 0-1min clips and 1-4min clips versus the entire clips in performing contrast-enhanced ultrasonography (CEUS) of focal liver lesions (FLLs). Methods: Contrast-enhanced ultrasonography (CEUS) examinations of 43 single FLLs were performed. All clips were analyzed in three ways, the entire clips, 0-1 min clips and 1-4 min clips, benign or malignant diagnosis and pathological diagnosis of each FLL were concluded by the three ways subsequently. Results: The results of correct diagnosis were assessed using Chi-square test. There was no difference with regard to benign or malignant diagnosis, between 0-1min clips and the entire clips, or between 1-4 min clips and the entire clips (p = 0.243 and p = 0.747, respectively). Moreover, no significant differences in pathological diagnosis existed between 0-1min clips and the entire clips, and 1- 4min clips versus entire clips (p=0.808 and p = 0.808, respectively). No significant differences existed among CEUS entire clip, 0-1min clip and 1-4min clip in identifying FLLs, and based on which the diagnosis of two different FLLs during CEUS with only one injection of contrast agent can be available. Conclusion: Only 0-1min clips or 1-4 min clips can be used to instead of the entre clip in performing CEUS of FLLs.

Sodium bicarbonate versus isotonic saline solution to prevent contrast-induced nephropathy: a systematic review and meta-analysis

Introduction: Contrast-induced nephropathy is one of the main causes of acute kidney injury and increased hospital-acquired morbidity and mortality. The use of sodium bicarbonate for nephroprotection has emerged as a preventative strategy; however, its efficacy is controversial compared to other strategies, such as hydration using 0.9% saline solution. Objective: To compare the effectiveness of sodium bicarbonate vs. hydration using 0.9% saline solution to prevent contrast-induced acute kidney injury. Methods: A systematic review of studies registered in the COCHRANE, PUBMED, MEDLINE, LILACS, SCIELO and EMBASE databases was conducted. Randomized controlled studies that evaluated the use of 0.9% saline solution vs. sodium bicarbonate to prevent contrast-induced nephropathy were included. Results: A total of 22 studies (5,686 patients) were included. Sodium bicarbonate did not decrease the risk of contrast-induced nephropathy (RD= 0.00; 95% CI= -0.02 to 0.03; p= 0.83; I2= 0%). No significant differences were found in the demand for renal replacement therapy (RD= 0.00; 95% CI= -0.01 to 0-01; I2= 0%; p= 0.99) or in mortality (RD= -0.00; 95% CI= -0.001 to 0.001; I2= 0%; p= 0.51). Conclusions: Sodium bicarbonate administration is not superior to the use of 0.9% saline solution for preventing contrast-induced nephropathy in patients with risk factors, nor is it better at reducing mortality or the need for renal replacement therapy.

INTEGRATION OF INSTRUMENTATION AND PROCESSING SOFTWARE OF A LASER SPECKLE CONTRAST IMAGING SYSTEM

Laser speckle contrast imaging (LSCI) has the potential to be a powerful tool in medicine, but more research in the field is required so it can be used properly. To help in the progression of Michigan Tech's research in the field, a graphical user interface (GUI) was designed in Matlab to control the instrumentation of the experiments as well as process the raw speckle images into contrast images while they are being acquired. The design of the system was successful and is currently being used by Michigan Tech's Biomedical Engineering department. This thesis describes the development of the LSCI GUI as well as offering a full introduction into the history, theory and applications of LSCI.

Binocular functional architecture for detection of contrast-modulated gratings

Combination of signals from the two eyes is the gateway to stereo vision. To gain insight into binocular signal processing, we studied binocular summation for luminance-modulated gratings (L or LM) and contrast-modulated gratings (CM). We measured 2AFC detection thresholds for a signal grating (0.75 c/deg, 216msec) shown to one eye, both eyes, or both eyes out-of-phase. For LM and CM, the carrier noise was in both eyes, even when the signal was monocular. Mean binocular thresholds for luminance gratings (L) were 5.4dB better than monocular thresholds - close to perfect linear summation (6dB). For LM and CM the binocular advantage was again 5-6dB, even when the carrier noise was uncorrelated, anti-correlated, or at orthogonal orientations in the two eyes. Binocular combination for CM probably arises from summation of envelope responses, and not from summation of these conflicting carrier patterns. Antiphase signals produced no binocular advantage, but thresholds were about 1-3dB higher than monocular ones. This is not consistent with simple linear summation, which should give complete cancellation and unmeasurably high thresholds. We propose a three-channel model in which noisy monocular responses to the envelope are binocularly combined in a contrast-weighted sum, but also remain separately available to perception via a max operator. Vision selects the largest of the three responses. With in-phase gratings the binocular channel dominates, but antiphase gratings cancel in the binocular channel and the monocular channels mediate detection. The small antiphase disadvantage might be explained by a subtle influence of background responses on binocular and monocular detection.

Contrast and lustre:a model that accounts for eleven different forms of contrast discrimination in binocular vision

Our goal here is a more complete understanding of how information about luminance contrast is encoded and used by the binocular visual system. In two-interval forced-choice experiments we assessed observers' ability to discriminate changes in contrast that could be an increase or decrease of contrast in one or both eyes, or an increase in one eye coupled with a decrease in the other (termed IncDec). The base or pedestal contrasts were either in-phase or out-of-phase in the two eyes. The opposed changes in the IncDec condition did not cancel each other out, implying that along with binocular summation, information is also available from mechanisms that do not sum the two eyes' inputs. These might be monocular mechanisms. With a binocular pedestal, monocular increments of contrast were much easier to see than monocular decrements. These findings suggest that there are separate binocular (B) and monocular (L,R) channels, but only the largest of the three responses, max(L,B,R), is available to perception and decision. Results from contrast discrimination and contrast matching tasks were described very accurately by this model. Stimuli, data, and model responses can all be visualized in a common binocular contrast space, allowing a more direct comparison between models and data. Some results with out-of-phase pedestals were not accounted for by the max model of contrast coding, but were well explained by an extended model in which gratings of opposite polarity create the sensation of lustre. Observers can discriminate changes in lustre alongside changes in contrast.