Synthetic Arterial Spin Labeling MRI of the Kidneys for Evaluation of Data Processing Pipeline

Accurate quantification of perfusion is crucial for diagnosis and monitoring of kidney function. Arterial spin labeling (ASL), a completely non-invasive magnetic resonance imaging technique, is a promising method for this application. However, differences in acquisition (e.g., ASL parameters, readout) and processing (e.g., registration, segmentation) between studies impede the comparison of results. To alleviate challenges arising solely from differences in processing pipelines, synthetic data are of great value. In this work, synthetic renal ASL data were generated using body models from the XCAT phantom and perfusion was added using the general kinetic model. Our in-house developed processing pipeline was then evaluated in terms of registration, quantification, and segmentation using the synthetic data. Registration performance was evaluated qualitatively with line profiles and quantitatively with mean structural similarity index measures (MSSIMs). Perfusion values obtained from the pipeline were compared to the values assumed when generating the synthetic data. Segmentation masks obtained by semi-automated procedure of the processing pipeline were compared to the original XCAT organ masks using the Dice index. Overall, the pipeline evaluation yielded good results. After registration, line profiles were smoother and, on average, MSSIMs increased by 25%. Mean perfusion values for cortex and medulla were close to the assumed perfusion of 250 mL/100 g/min and 50 mL/100 g/min, respectively. Dice indices ranged 0.80–0.93, 0.78–0.89, and 0.64–0.84 for whole kidney, cortex, and medulla, respectively. The generation of synthetic ASL data allows flexible choice of parameters and the generated data are well suited for evaluation of processing pipelines.

Development of an abdominal phantom for the validation of an oligometastatic disease diagnosis workflow

PURPOSE

The liver is a common site for metastatic disease, which is a challenging and life-threatening condition with a grim prognosis and outcome. We propose a standardized workflow for the diagnosis of oligometastatic disease (OMD), as a gold standard workflow has not been established yet. The envisioned workflow comprises the acquisition of a multimodal image dataset, novel image processing techniques, and cone beam computed tomography (CBCT)-guided biopsy for subsequent molecular subtyping. By combining morphological, molecular, and functional information about the tumor, a patient-specific treatment planning is possible. We designed and manufactured an abdominal liver phantom that we used to demonstrate multimodal image acquisition, image processing, and biopsy of the OMD diagnosis workflow.

METHODS

The anthropomorphic abdominal phantom contains a rib cage, a portal vein, lungs, a liver with six lesions, and a hepatic vessel tree. This phantom incorporates three different lesion types with varying visibility under computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography CT (PET-CT), which reflects clinical reality. The phantom is puncturable and the size of the corpus and the organs is comparable to those of a real human abdomen. By using several modern additive manufacturing techniques, the manufacturing process is reproducible and allows to incorporate patient-specific anatomies. As a first step of the OMD diagnosis workflow, a pre-interventional CT, MRI, and PET-CT dataset of the phantom was acquired. The image information was fused using image registration and organ information was extracted via image segmentation. A CBCT-guided needle puncture experiment was performed, where all six liver lesions were punctured with coaxial biopsy needles.

RESULTS

Qualitative observation of the image data and quantitative evaluation using contrast-to-noise ratio (CNR) confirms that one lesion type is visible only in MRI and not CT. The other two lesion types are visible in CT and MRI. The CBCT-guided needle placement was performed for all six lesions, including those visible only in MRI and not CBCT. This was possible by successfully merging multimodal pre-interventional image data. Lungs, bones, and liver vessels serve as realistic inhibitions during needle path planning.

CONCLUSIONS

We have developed a reusable abdominal phantom that has been used to validate a standardized OMD diagnosis workflow. Utilizing the phantom, we have been able to show that a multimodal imaging pipeline is advantageous for a comprehensive detection of liver lesions. In a CBCT-guided needle placement experiment we have punctured lesions that are invisible in CBCT using registered pre-interventional MRI scans for needle path planning. This article is protected by copyright. All rights reserved.

Fast CBCT Reconstruction using Convolutional Neural Networks for Arbitrary Robotic C-arm Orbits

Cone-beam CT (CBCT) with non-circular acquisition orbits has the potential to improve image quality, increase the field-of view, and facilitate minimal interference within an interventional imaging setting. Because time is of the essence in interventional imaging scenarios, rapid reconstruction methods are advantageous. Model-Based Iterative Reconstruction (MBIR) techniques implicitly handle arbitrary geometries; however, the computational burden for these approaches is particularly high. The aim of this work is to extend a previously proposed framework for fast reconstruction of non-circular CBCT trajectories. The pipeline combines a deconvolution operation on the backprojected measurements using an approximate, shift-invariant system response prior to processing with a Convolutional Neural Network (CNN). We trained and evaluated the CNN for this approach using 1800 randomized arbitrary orbits. Noisy projection data were formed from 1000 procedurally generated tetrahedral phantoms as well as anthropomorphic data in the form of 800 CT and CBCT images from the Lung Image Database Consortium Image Collection (LIDC). Using this proposed reconstruction pipeline, computation time was reduced by 90% as compared to MBIR with only minor differences in performance. Quantitative comparisons of nRMSE, FSIM and SSIM are reported. Performance was consistent for projection data simulated with acquisition orbits the network has not previously been trained on. These results suggest the potential for fast processing of arbitrary CBCT trajectory data with reconstruction times that are clinically relevant and applicable - facilitating the application of non-circular orbits in CT image-guided interventions and intraoperative imaging.

Automated Screening for Abdominal Aortic Aneurysm in CT Scans under Clinical Conditions Using Deep Learning

Abdominal aortic aneurysms (AAA) may remain clinically silent until they enlarge and patients present with a potentially lethal rupture. This necessitates early detection and elective treatment. The goal of this study was to develop an easy-to-train algorithm which is capable of automated AAA screening in CT scans and can be applied to an intra-hospital environment. Three deep convolutional neural networks (ResNet, VGG-16 and AlexNet) were adapted for 3D classification and applied to a dataset consisting of 187 heterogenous CT scans. The 3D ResNet outperformed both other networks. Across the five folds of the first training dataset it achieved an accuracy of 0.856 and an area under the curve (AUC) of 0.926. Subsequently, the algorithms performance was verified on a second data set containing 106 scans, where it ran fully automated and resulted in an accuracy of 0.953 and an AUC of 0.971. A layer-wise relevance propagation (LRP) made the decision process interpretable and showed that the network correctly focused on the aortic lumen. In conclusion, the deep learning-based screening proved to be robust and showed high performance even on a heterogeneous multi-center data set. Integration into hospital workflow and its effect on aneurysm management would be an exciting topic of future research.

An anthropomorphic pelvis phantom for MR-guided prostate interventions

PURPOSE

To design and manufacture a pelvis phantom for magnetic resonance (MR)-guided prostate interventions, such as MRGB (MR-guided biopsy) or brachytherapy seed placement.

METHODS

The phantom was designed to mimic the human pelvis incorporating bones, bladder, prostate with four lesions, urethra, arteries, veins, and six lymph nodes embedded in ballistic gelatin. A hollow rectum enables transrectal access to the prostate. To demonstrate the feasibility of the phantom for minimal invasive MRI-guided interventions, a targeted inbore MRGB was performed. The needle probe was rectally inserted and guided using an MRI-compatible remote controlled manipulator (RCM).

RESULTS

The presented pelvis phantom has realistic imaging properties for MR imaging (MRI), computed tomography (CT) and ultrasound (US). In the targeted inbore MRGB, a prostate lesion was successfully hit with an accuracy of 3.5 mm. The experiment demonstrates that the limited size of the rectum represents a realistic impairment for needle placements.

CONCLUSION

The phantom provides a valuable platform for evaluating the performance of MRGB systems. Interventionalists can use the phantom to learn how to deal with challenging situations, without risking harm to patients.

[MRI-guided minimally invasive treatment of prostate cancer]

CLINICAL/METHODOLOGICAL ISSUE

Multiparametric magnetic resonance imaging (mpMRI) of the prostate plays a crucial role in the diagnosis and local staging of primary prostate cancer.

STANDARD RADIOLOGICAL METHODS

Image-guided biopsy techniques such as MRI-ultrasound fusion not only allow guidance for targeted tissue sampling of index lesions for diagnostic confirmation, but also improve the detection of clinically significant prostate cancer.

METHODOLOGICAL INNOVATIONS

Minimally invasive, focal therapies of localized prostate cancer complement the treatment spectrum, especially for low- and intermediate-risk patients.

PERFORMANCE

In patients of low and intermediate risk, MR-guided, minimally invasive therapies could enable local tumor control, improved functional outcomes and possible subsequent therapy escalation. Further study results related to multimodal approaches and the application of artificial intelligence (AI) by machine and deep learning algorithms will help to leverage the full potential of focal therapies for prostate cancer in the upcoming era of precision medicine.

ACHIEVEMENTS

Completion of ongoing randomized trials comparing each minimally invasive therapy approach with established whole-gland procedures is needed before minimally invasive therapies can be implemented into existing treatment guidelines.

PRACTICAL RECOMMENDATIONS

This review article highlights minimally invasive therapies of prostate cancer and the key role of mpMRI for planning and conducting these therapies.

Comparison of the test-retest reliability of the Work Box using three administrative methods

OBJECTIVE

The purpose of this study was to compare the test-retest reliability of three administrative methods of the Work Box: (a) the original instructions, (b) a revised version of the original instructions, and (c) another revised version that was based on suggestions made by authors of the first two versions of the instructions.

METHOD

Sixty subjects without disabilities were randomly grouped so that 20 subjects were tested per administrative method. The assessment was administered to each subject on two occasions, with a 7-day to 14-day period between tests. Scores were recorded as time in seconds, and intraclass correlation coefficients (ICCs) were used to calculate the reliability.

RESULTS

The ICCs for assembly, disassembly, and total scores were .589, .604, and .654, respectively, for the original instructions; .424, .572, and .545 for the revised instructions; and .781, .579, .717 for the second revised instructions. Reliability was found to be higher for men than for women and for subjects who claimed to have more rather than less experience in similar manual dexterity tasks.

CONCLUSIONS

On the basis of the reliability of each administrative method and comments made by subjects about their understanding of the instructions, the second revised version of the instructions is recommended as the standard method. The results also indicate that the assessment is most appropriate for a population of men with manual dexterity experience. With further standardization, the Work Box could be a valuable assessment tool for therapists working in industrial rehabilitation settings.

Adult physical dysfunction content in professional curricula

This study examined the content of occupational therapy professional curricula as it pertains to adult physical dysfunction and the opinions and perceptions of faculty responsible for this content area. Survey results from 28 of 66 academic institutions offering professional-level education were received and analyzed. A great diversity in content and emphasis was reflected in the areas of medical conditions, general approaches to evaluation and treatment, specific evaluations, and specific treatment techniques and modalities. Most of the respondents were pleased with students' performances in physical dysfunction Level II fieldwork, believed that course work was applicable to local clinical settings, and agreed that courses were constantly changing to reflect evolving occupational therapy theory. Approximately 30% of the respondents believed that they had inadequate time to prepare students for entry-level practice, and about half agreed that their department had the necessary equipment to teach evaluation and treatment content.

The assessment of occupational functioning: a screening tool for use in long-term care

This paper describes the development of the Assessment of Occupational Functioning (AOF), a screening tool designed to assess the functional capacity of residents in long-term treatment settings who have physical and/or psychiatric problems. The assessment is based on six variables of the Model of Human Occupation. A study of 83 community and institutionalized elderly subjects was conducted to examine the AOF's dimensionality, test-retest reliability, interrater reliability, concurrent validity, and ability to discriminate between healthy and institutionalized adults. Item analysis suggests that ratings tend to correspond with components of the theoretical model. Both test-retest reliability and interrater reliability correlations for total test scores were above accepted minimum levels. Correlations of the screening tool with scores on the Life Satisfaction Index-Z, a concurrent validity measure, yielded positive correlations. Correlations of the screening tool score with another concurrent validity measure, the Geriatric Rating Scale score, yielded mixed results. Discrimination results indicated that the instrument can distinguish between the adaptive performance of normal and institutionalized populations.

Circular triads when not all paired comparisons are made

In paired comparison experiments, especially those involving sensory perception, it is sometimes impossible or undesirable to perform all possible comparisons. As when all comparisons are made, the number of circular triads can be used as a measure of inconsistency in the responses of a particular judge. A computational method for determining the number of circular triads is presented in this paper.