Ferdi van der Heijden

Concomitant speed-of-sound tomography in photoacoustic imaging

We present a method to generate quantitative cross-sectional maps of acoustic propagation speed in tissue using the photoacoustic principle. The method is based on the interaction of laser-induced ultrasound from an extraneous absorber with the object under photoacoustic investigation. The propagation times of the ultrasound transients through the object at angles around 360° are measured using a multielement ultrasound detector. The geometry lends itself to fan-beam reconstruction allowing speed-of-sound tomograms to be generated. Simultaneously, conventional photoacoustic computed tomography can be performed as well. We demonstrate the concept showing results on phantoms carrying speed-of-sound distributions.

Infrared thermal imaging for automated detection of diabetic foot complications.

Background: Although thermal imaging can be a valuable technology in the prevention and management of diabetic foot disease, it is not yet widely used in clinical practice. Technological advancement in infrared imaging increases its application range. The aim was to explore the first steps in the applicability of high-resolution infrared thermal imaging for noninvasive automated detection of signs of diabetic foot disease. Methods: The plantar foot surfaces of 15 diabetes patients were imaged with an infrared camera (resolution, 1.2 mm/pixel): 5 patients had no visible signs of foot complications, 5 patients had local complications (e.g., abundant callus or neuropathic ulcer), and 5 patients had diffuse complications (e.g., Charcot foot, infected ulcer, or critical ischemia). Foot temperature was calculated as mean temperature across pixels for the whole foot and for specified regions of interest (ROIs). Results: No differences in mean temperature >1.5 °C between the ipsilateral and the contralateral foot were found in patients without complications. In patients with local complications, mean temperatures of the ipsilateral and the contralateral foot were similar, but temperature at the ROI was >2 °C higher compared with the corresponding region in the contralateral foot and to the mean of the whole ipsilateral foot. In patients with diffuse complications, mean temperature differences of >3 °C between ipsilateral and contralateral foot were found. Conclusions: With an algorithm based on parameters that can be captured and analyzed with a high-resolution infrared camera and a computer, it is possible to detect signs of diabetic foot disease and to discriminate between no, local, or diffuse diabetic foot complications. As such, an intelligent telemedicine monitoring system for noninvasive automated detection of signs of diabetic foot disease is one step closer. Future studies are essential to confirm and extend these promising early findings.

Diagnostic Values for Skin Temperature Assessment to Detect Diabetes-Related Foot Complications

BACKGROUND Skin temperature assessment is a promising modality for early detection of diabetic foot problems, but its diagnostic value has not been studied. Our aims were to investigate the diagnostic value of different cutoff skin temperature values for detecting diabetes-related foot complications such as ulceration, infection, and Charcot foot and to determine urgency of treatment in case of diagnosed infection or a red-hot swollen foot. MATERIALS AND METHODS The plantar foot surfaces of 54 patients with diabetes visiting the outpatient foot clinic were imaged with an infrared camera. Nine patients had complications requiring immediate treatment, 25 patients had complications requiring non-immediate treatment, and 20 patients had no complications requiring treatment. Average pixel temperature was calculated for six predefined spots and for the whole foot. We calculated the area under the receiver operating characteristic curve for different cutoff skin temperature values using clinical assessment as reference and defined the sensitivity and specificity for the most optimal cutoff temperature value. Mean temperature difference between feet was analyzed using the Kruskal-Wallis tests. RESULTS The most optimal cutoff skin temperature value for detection of diabetes-related foot complications was a 2.2°C difference between contralateral spots (sensitivity, 76%; specificity, 40%). The most optimal cutoff skin temperature value for determining urgency of treatment was a 1.35°C difference between the mean temperature of the left and right foot (sensitivity, 89%; specificity, 78%). CONCLUSIONS Detection of diabetes-related foot complications based on local skin temperature assessment is hindered by low diagnostic values. Mean temperature difference between two feet may be an adequate marker for determining urgency of treatment.

Infrared dermal thermography on diabetic feet soles to predict ulcerations: a case study

Diabetic foot ulceration is a major complication for patients with diabetes mellitus. If not adequately treated, these ulcers may lead to foot infection, and ultimately to lower extremity amputation, which imposes a major burden to society and great loss in health-related quality of life for patients. Early identification and subsequent preventive treatment have proven useful to limit the incidence of foot ulcers and lower extremity amputation. Thus, the development of new diagnosis tools has become an attractive option. The ultimate objective of our project is to develop an intelligent telemedicine monitoring system for frequent examination on patients’ feet, to timely detect pre-signs of ulceration. Inflammation in diabetic feet can be an early and predictive warning sign for ulceration, and temperature has been proven to be a vicarious marker for inflammation. Studies have indicated that infrared dermal thermography of foot soles can be one of the important parameters for assessing the risk of diabetic foot ulceration. This paper covers the feasibility study of using an infrared camera, FLIR SC305, in our setup, to acquire the spatial thermal distribution on the feet soles. With the obtained thermal images, automated detection through image analysis was performed to identify the abnormal increased/decreased temperature and assess the risk for ulceration. The thermography for feet soles of patients with diagnosed diabetic foot complications were acquired before the ordinary foot examinations. Assessment from clinicians and thermography were compared and follow-up measurements were performed to investigate the prediction. A preliminary case study will be presented, indicating that dermal thermography in our proposed setup can be a screening modality to timely detect pre-signs of ulceration.

Imaging of acoustic attenuation and speed of sound maps using photoacoustic measurements

Photoacoustic imaging is an upcoming medical imaging modality with the potential of imaging both optical and acoustic properties of objects. We present a measurement system and outline reconstruction methods to image both speed of sound and acoustic attenuation distributions of an object using only pulsed light excitation. These acoustic properties can be used in a subsequent step to improve the image quality of the optical absorption distribution. A passive element, which is a high absorbing material with a small cross-section such as a carbon fiber, is introduced between the light beam and the object. This passive element acts as a photoacoustic source and measurements are obtained by allowing the generated acoustic signal to propagate through the object. From these measurements we can extract measures of line integrals over the acoustic property distribution for both the speed of sound and the acoustic attenuation. Reconstruction of the acoustic property distributions then comes down to the inversion of a linear system relating the obtained projection measurements to the acoustic property distributions. We show the results of applying our approach on phantom objects. Satisfactory results are obtained for both the reconstruction of speed of sound and the acoustic attenuation.

Colonoscopy with robotic steering and automated lumen centralization: a feasibility study in a colon model.

BACKGROUND AND STUDY AIMS We introduced a new platform for performing colonoscopy with robotic steering and automated lumen centralization (RS-ALC) and evaluated its technical feasibility. PARTICIPANTS AND METHODS Expert endoscopists (n = 8) and endoscopy-naive novices (n = 10) used conventional steering and RS-ALC to perform colonoscopy in a validated colon model with simulated polyps (n = 21). The participants were randomized to which modality they were to use first. End points were the cecal intubation time, number of detected polyps, and subjective evaluation of the platform. RESULTS Novices were able to intubate the cecum faster with RS-ALC (median 8 minutes [min] 56 seconds [s], interquartile range [IQR] 6  min 46  s - 16  min 34  s vs. median 11  min 47  s, IQR 8  min 19  s - 15  min 33  s, P = 0.65), whereas experts were faster with conventional steering (median 2  min 9  s, IQR 1  min 13 s - 7  min 28  s vs. median 13  min 1  s, IQR 5  min 9 s - 16  min 54  s, P = 0.12). Novices detected more polyps with RS-ALC (median 88.1 %, IQR 79.8 % - 95.2 % vs. median 78.6 %, IQR 75.0 % - 91.7 %, P = 0.17), whereas experts detected more polyps with conventional steering (median 80.9 %, IQR 76.2 % - 85.7 % vs. median 69.0 %, IQR 61.0 % - 75.0 %, P = 0.03). Novices were more positive than experts about the new platform (P = 0.02), noting an easier and faster introduction of the colonoscope with RS-ALC than with conventional steering. CONCLUSIONS Colonoscopy with RS-ALC is technically feasible and appears to be easier and more intuitive than conventional steering for endoscopy-naive novices.

Statistical analysis of spectral data: a methodology for designing an intelligent monitoring system for the diabetic foot

Abstract. Early detection of (pre-)signs of ulceration on a diabetic foot is valuable for clinical practice. Hyperspectral imaging is a promising technique for detection and classification of such (pre-)signs. However, the number of the spectral bands should be limited to avoid overfitting, which is critical for pixel classification with hyperspectral image data. The goal was to design a detector/classifier based on spectral imaging (SI) with a small number of optical bandpass filters. The performance and stability of the design were also investigated. The selection of the bandpass filters boils down to a feature selection problem. A dataset was built, containing reflectance spectra of 227 skin spots from 64 patients, measured with a spectrometer. Each skin spot was annotated manually by clinicians as “healthy” or a specific (pre-)sign of ulceration. Statistical analysis on the data set showed the number of required filters is between 3 and 7, depending on additional constraints on the filter set. The stability analysis revealed that shot noise was the most critical factor affecting the classification performance. It indicated that this impact could be avoided in future SI systems with a camera sensor whose saturation level is higher than 106, or by postimage processing.

Simultaneous imaging of ultrasound attenuation, speed of sound, and optical absorption in a photoacoustic setup

Photoacoustic imaging is a relatively new medical imaging modality. In principle it can be used to image the optical absorption distribution of an object by measurements of optically induced acoustic signals. Recently we have developed a modified photoacoustic measurement system which can be used to simultaneously image the ultrasound propagation parameters as well. By proper placement of a passive element we obtain isolated measurements of the objects ultrasound propagation parameters, independent of the optical absorption inside the object. This passive element acts as a photoacoustic source and measurements are obtained by allowing the generated ultrasound signal to propagate through the object. Images of the ultrasound propagation parameters, being the attenuation and speed of sound, can then be reconstructed by inversion of a measurement model. This measurement model relates the projections non-linearly to the unknown images, due to ray refraction effects. After estimating the speed of sound and attenuation distribution, the optical absorption distribution is reconstructed. In this reconstruction problem we take into account the previously estimated speed of sound distribution. So far, the reconstruction algorithms have been tested using computer simulations. The method has been compared with existing algorithms and good results have been obtained.

A preliminary evaluation of a flexible needle steering algorithm using magnetic resonance images as feedback

Needle-based procedures are commonly performed for cancer diagnosis and treatment. Imaging modalities are used to visualize the needle tip and the target during these needle insertion procedures. Among the available imaging techniques, magnetic resonance (MR) offers the best tissue contrast, where detection of an early stage cancer is possible. MR-guided needle insertions are currently performed with rigid needles, which have limited steerability. Flexible needles have been introduced to increase the steerability during the insertion. In this paper, we present a preliminary evaluation of a steering method for flexible bevel-tipped needles using MR as an imaging modality. The steering algorithm uses a needle deflection model to predict the tip motion and calculate the optimal rotation to reach the target. The best sequence of rotations are defined by an optimization algorithm based on the Nelder-Mead technique. The needle tip and the target are manually tracked through a graphical user interface. The needle is inserted by a device fabricated with MR-compatible material. The MR-guided flexible needle steering is evaluated by a series of insertions in two phantoms with real obstacles and targets. The average targeting error with flexible needles is 4.3mm, which is 28% lower than the values reported in the literature with rigid needles. The results indicate the feasibility of MR-guided flexible needle insertions.

Image-Based Navigation for a Robotized Flexible Endoscope

Robotizing flexible endoscopy enables image-based control of endoscopes. Especially during high-throughput procedures, such as a colonoscopy, navigation support algorithms could improve procedure turnaround and ergonomics for the endoscopist.