Recent advances in medical imaging: anatomical and clinical applications

Estimation for the bivariate quantile varying coefficient model with application to diffusion tensor imaging data analysis

Despite interest in the joint modeling of multiple functional responses such as diffusion properties in neuroimaging, robust statistical methods appropriate for this task are lacking. To address this need, we propose a varying coefficient quantile regression model able to handle bivariate functional responses. Our work supports innovative insights into biomedical data by modeling the joint distribution of functional variables over their domains and across clinical covariates. We propose an estimation procedure based on the alternating direction method of multipliers and propagation separation algorithms to estimate varying coefficients using a B-spline basis and an $L_2$ smoothness penalty that encourages interpretability. A simulation study and an application to a real-world neurodevelopmental data set demonstrates the performance of our model and the insights provided by modeling functional fractional anisotropy and mean diffusivity jointly and their association with gestational age and sex.

Automatic tool segmentation and tracking during robotic intravascular catheterization for cardiac interventions

Background

Cardiovascular diseases resulting from aneurism, thrombosis, and atherosclerosis in the cardiovascular system are major causes of global mortality. Recent treatment methods have been based on catheterization of flexible endovascular tools with imaging guidance. While advances in robotic intravascular catheterization have led to modeling tool navigation approaches with data sensing and feedback, proper adaptation of image-based guidance for robotic navigation requires the development of sensitive segmentation and tracking models without specificity loss. Several methods have been developed to tackle non-uniform illumination, low contrast; however, presence of untargeted body organs commonly found in X-ray frames taken during angiography procedures still presents some major issues to be solved.

Methods

In this study, a segmentation method was developed for automatic detection and tracking of guidewire pixels in X-ray angiograms. Image frames were acquired during robotic intravascular catheterization for cardiac interventions. For segmentation, multiscale enhancement filtering was applied on preprocessed X-ray angiograms, while morphological operations and filters were applied to refine the frames for pixel intensity adjustment and vesselness measurement. Minima and maxima extrema of the pixels were obtained to detect guidewire pixels in the X-ray frames. Lastly, morphological operation was applied for guidewire pixel connectivity and tracking in segmented pixels. Method validation was performed on 12 X-ray angiogram sequences which were acquired during in vivo intravascular catheterization trials in rabbits.

Results

The study outcomes showed that an overall accuracy of 0.995±0.001 was achieved for segmentation. Tracking performance was characterized with displacement and orientation errors observed as 1.938±2.429 mm and 0.039±0.040°, respectively. Evaluation studies performed against 9 existing methods revealed that this proposed method provides more accurate segmentation with 0.753±0.074 area under curve. Simultaneously, high tracking accuracy of 0.995±0.001 with low displacement and orientation errors of 1.938±2.429 mm and 0.039±0.040°, respectively, were achieved. Also, the method demonstrated higher sensitivity and specificity values compared to the 9 existing methods, with a relatively faster exaction time.

Conclusions

The proposed method has the capability to enhance robotic intravascular catheterization during percutaneous coronary interventions (PCIs). Thus, interventionists can be provided with better tool tracking and visualization systems while also reducing their exposure to operational hazards during intravascular catheterization for cardiac interventions.

The Anatomy of the Frontal Process of the Maxilla in the Medial Wall of the Lacrimal Drainage System in East Asians

PURPOSE

To investigate the anatomical structure characteristics of the frontal process of the maxilla in the medial wall of the lacrimal drainage system for endoscopic dacryocystorhinostomy based on the cone-beam computed tomography images.

METHODS

One hundred eight sides of orbits were retrospectively evaluated in this study. The angulation and thickness of the frontal process of the maxilla in the medial wall of the lacrimal drainage system were measured and compared at 2 different levels: lacrimal sac level and nasolacrimal duct level. The vertical height between the 2 measurement levels was also measured. Data were compared between males and females.

RESULTS

The average angulation and thickness of the frontal process of the maxilla were found significantly larger at the lacrimal sac level than at the nasolacrimal duct level (83.1 ± 11.3° vs. 61.7 ± 10.9° and 2.7 ± 0.9 mm vs. 1.1 ± 0.4 mm) (p < 0.001). The vertical height between the 2 levels was significantly higher in males than in females (8.6 ± 1.8 mm vs. 7.8 ± 1.7 mm) (p = 0.015).

CONCLUSIONS

We found the angulation and thickness of the frontal process of the maxilla in the medial wall of the lacrimal drainage system decreased from the upper to the lower level. Starting the osteotomy during endoscopic dacryocystorhinostomy might be easier and safer at the midpoint level of the maxillary line.

Teaching medical anatomy: what is the role of imaging today?

PURPOSE

Medical anatomy instruction has been an important issue of debate for many years and imaging anatomy has become an increasingly important component in the field, the role of which has not yet been clearly defined. The aim of the paper was to assess the current deployment of medical imaging in the teaching of anatomy by means of a review of the literature.

MATERIALS

A systematic search was performed using the electronic database PubMed, ScienceDirect and various publisher databases, with combinations of the relevant MeSH terms. A manual research was added.

RESULTS

In most academic curricula, imaging anatomy has been integrated as a part of anatomical education, taught using a very wide variety of strategies. Considerable variation in the time allocation, content and delivery of medical imaging in teaching human anatomy was identified. Given this considerable variation, an objective assessment remains quite difficult.

DISCUSSION

In most publications, students' perceptions regarding anatomical courses including imaging anatomy were investigated by means of questionnaires and, regardless of the method of teaching, it was globally concluded that imaging anatomy enhanced the quality and efficiency of instruction in human anatomy. More objective evaluation based on an increase in students' performance on course examinations or on specific tests performed before and after teaching sessions showed positive results in numerous cases, while mixed results were also indicated by other studies.

CONCLUSION

A relative standardization could be useful in improving the teaching of imaging anatomy, to facilitate its assessment and reinforce its effectiveness.

Morphological concordance between CBCT and MDCT: a paranasal sinus-imaging anatomical study

PURPOSE

Cone-beam computed tomography (CBCT) is an imaging technique, first developed for use during oral and pre-implant surgery. In sinonasal surgery, CBCT might represent a valuable tool for anatomical research given its high spatial resolution and low irradiation dose. However, clinical and anatomical evidence pertaining to its efficacy is lacking. This study assessed the morphological concordance between CBCT and multislice detector computed tomography (MDCT) in the context of sinonasal anatomy.

METHODS

We performed an anatomical study using 15 fresh cadaver heads. Each head underwent both CBCT and MDCT. Two independent reviewers evaluated 26 notable anatomical landmarks. The primary outcome was the overall morphological concordance between the two imaging techniques. Secondary objectives included assessment of inter-rater agreement and comparison of the radiation doses received by different parts of the anatomy.

RESULTS

Overall morphological concordance between the two imaging techniques was excellent (>98 %); the inter-rater agreement for CBCT was approximately 97 %, which is highly similar to MDCT, but achieved using a significantly decreased irradiation dose.

CONCLUSION

Our preliminary study indicates that CBCT represents a valid, reproducible, and safe technique for the identification of relevant sinonasal anatomical structures. Further research, particularly in pathological contexts, is required.

Visualization techniques of the inferior alveolar nerve (IAN): a narrative review

Purpose

The purpose of this study was to produce an overview of the present visualization techniques of the inferior alveolar nerve (IAN) in order to reduce the rates of nerve damage after third molar (M3) removal and bilateral sagittal split osteotomy (BSSO).

Methods

An electronic literature search was performed of the English-language scientific literature published prior to December 31, 2014 using the LIMO KU Leuven search platform. Information on the specifications of the different imaging techniques, their clinical application, advantages, disadvantages, and duration was extracted from 11 reports.

Results

Five methods for IAN visualization were obtained from the search results, which are cone-beam computed tomography (CBCT) and automatic extraction of the IAN canal using computed tomography (CT), magnetic resonance imaging (MRI), panoramic radiography, endoscopy, and ultrasonographic visualization.

Conclusion

The results of this study suggest that high-resolution MRI is the most commonly used method for direct visualization of the IAN. Six out of the eleven manuscripts use this technique. Recently, there have been some (experimental) modifications to the conventional MRI in the form of diffusion tensor tractography (DTT), phase-contrast magnetic resonance angiography (PC-MRA), and dental MRI. Future studies will focus on an intraoperative application of MRI to visualize the IAN during surgery.

Review on the characteristics of radiation detectors for dosimetry and imaging

The enormous advances in the understanding of human anatomy, physiology and pathology in recent decades have led to ever-improving methods of disease prevention, diagnosis and treatment. Many of these achievements have been enabled, at least in part, by advances in ionizing radiation detectors. Radiology has been transformed by the implementation of multi-slice CT and digital x-ray imaging systems, with silver halide films now largely obsolete for many applications. Nuclear medicine has benefited from more sensitive, faster and higher-resolution detectors delivering ever-higher SPECT and PET image quality. PET/MR systems have been enabled by the development of gamma ray detectors that can operate in high magnetic fields. These huge advances in imaging have enabled equally impressive steps forward in radiotherapy delivery accuracy, with 4DCT, PET and MRI routinely used in treatment planning and online image guidance provided by cone-beam CT. The challenge of ensuring safe, accurate and precise delivery of highly complex radiation fields has also both driven and benefited from advances in radiation detectors. Detector systems have been developed for the measurement of electron, intensity-modulated and modulated arc x-ray, proton and ion beams, and around brachytherapy sources based on a very wide range of technologies. The types of measurement performed are equally wide, encompassing commissioning and quality assurance, reference dosimetry, in vivo dosimetry and personal and environmental monitoring. In this article, we briefly introduce the general physical characteristics and properties that are commonly used to describe the behaviour and performance of both discrete and imaging detectors. The physical principles of operation of calorimeters; ionization and charge detectors; semiconductor, luminescent, scintillating and chemical detectors; and radiochromic and radiographic films are then reviewed and their principle applications discussed. Finally, a general discussion of the application of detectors for x-ray nuclear medicine and ion beam imaging and dosimetry is presented.

Nonvascular and portal vein applications of cone-beam computed tomography: current status

C-arm cone-beam computed tomography (CBCT) is a relatively new imaging technology that uses a conical-shaped radiation beam and a 2-dimensional flat-panel detector to produce 3-dimensional volumetric datasets with excellent spatial resolution. Recently, this technology has been implemented in angiographic units across the country. This imaging modality is particularly useful when both images of "CT-like" quality and real-time fluoroscopic imaging are required for pretreatment planning and intraprocedural guidance. In this article, we describe the use of cone-beam CT technology in various nonvascular and portal venous interventions, including percutaneous vertebroplasty or kyphoplasty, transjugular intrahepatic portosystemic shunt, percutaneous needle biopsy and ablation of pulmonary nodules and renal masses, gastrostomy tube insertion, hepatic radiofrequency ablation, and biliary interventions.

Use of CBCT to investigate the root canal morphology of mandibular incisors

PURPOSE

To investigate the root canal morphology of mandibular incisors using cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

A total of 353 patients with 1,412 healthy, well-developed mandibular incisors were enrolled. Radiographic examination by CBCT was conducted as part of their routine examination, diagnosis and treatment planning. The following observations were made using CBCT: (1) the number of roots; (2) the number of canals; (3) canal configuration according to Vertucci's classification; (4) the position of root canal bifurcations.

RESULTS

Two canals were found in 10.9 % of mandibular central incisors, 25.5 % of lateral incisors and in 18.2 % of all the 1,412 mandibular incisors. Significantly, more lateral incisors possessed two canals than central incisors (p < 0.05). Of the teeth with two canals, type III incisors were the most prevalent, followed by types II, IV and V. Furthermore, 37.7 % of teeth were found to have root canal bifurcations that were at or near to the cortical-middle third junction regions of the roots.

CONCLUSION

Routine mode CBCT imaging was clinically useful for detection of two canals and determines the position of root canal bifurcations in mandibular incisors.

Decreased white matter integrity in fronto-occipital fasciculus bundles: relation to visual information processing in alcohol-dependent subjects

Chronic alcohol abuse is characterized by impaired cognitive abilities with a more severe deficit in visual than in verbal functions. Neuropathologically, it is associated with widespread brain structural compromise marked by gray matter shrinkage, ventricular enlargement, and white matter degradation. The present study sought to increase current understanding of the impairment of visual processing abilities in alcohol-dependent subjects, and its correlation with white matter microstructural alterations, using diffusion tensor imaging (DTI). To that end, a DTI study was carried out on 35 alcohol-dependent subjects and 30 healthy male control subjects. Neuropsychological tests were assessed for visual processing skills and deficits were reported as raw dysfunction scores (rDyS). Reduced FA (fractional anisotropy) and increased MD (mean diffusivity) were observed bilaterally in inferior and superior fronto-occipital fasciculus (FOF) fiber bundles. A significant inverse correlation in rDyS and FA values was observed in these fiber tracts whereas a positive correlation of these scores was found with the MD values. Our results suggest that FOF fiber bundles linking the frontal lobe to occipital lobe might be related to visual processing skills. This is the first report of an alteration of the white matter microstructure of FOF fiber bundles that might have functional consequences for visual processing in alcohol-dependent subjects who exhibit no neurological complications.