Ozgur Kocaturk

An acousto-optic (AO)-based electric field sensor is presented for time domain measurement under magnetic resonance imaging (MRI). A fully MR-compatible sensor is designed and fabricated using a phase-shifted fiber Bragg grating mechanically coupled to a piezoelectric transducer. Mechanical resonance of the piezoelectric transducer is matched to the operating frequencies of commonly used MRI systems to increase the sensitivity of the sensor. Sensitivity of the sensor is measured as 1.27 mV/V/m, with a minimum detectable electric field of 4.4 mV/m/√Hz. Directivity of the sensor is measured with a 18 dB orthogonal component rejection. The dynamic range of the sensor is calculated as 117 dB/Hz, which allows the measurement of electric fields up to 3.2 kV/m. In MRI studies, the AO sensor was able detect local hot spots around a reference implant accurately with high signal-to-noise ratio. AO sensor exhibited similar or better performance when compared with commercially available MRI compatible electric field sensors. Furthermore, the small size of the sensor with the flexible fiber optic link could allow in situ measurements of electric fields during critical interventional procedures such as pacemaker lead or deep brain stimulator placement as an MRI dosimeter during diagnostic scans.

Critical limb ischemia (CLI) is the most severe form of peripheral arterial disease (PAD) which induces extremity rest pain, extremity gangrene or ulcers that mostly might lead to limb loss. One of the most common criteria of CLI is 50 mmHg or less systolic ankle arterial pressure. In this study, a custom made three-lumen catheter (9 Fr) including a distal inflatable balloon in between the inflow and outflow lumen holes was designed and fabricated based on the patented design of Hyper Perfusion Catheter. The proposed catheter design aims to increase ankle systolic pressure to 60 mmHg or more to promote healing and/or alleviating severe pain due to intractable ischemia for patients with CLI. To simulate the blood circulation of related anatomy, in vitro CLI model phantom was designed and constructed by using a modified hemodialysis circuit, a hemodialysis pump and a tube set for cardio-pulmonary bypass surgery. A blood mimicking fluid (BMF) with dynamic viscosity of 4.1 mPa.s was used at 22 ºC to prime the phantom. The data was collected by a custom-made circuit design in real time and all measurements were verified with commercial certificated medical devices. The results of in vitro CLI model phantom experiments have shown that it is feasible to elevate the pressure distal to the occlusion (representing ankle pressure) above 80 mmHg without affecting the systemic pressure.

In clinical routine, the prostate biopsy procedure is performed with the guidance of transrectal ultrasound (TRUS) imaging to diagnose prostate cancer. However, the TRUS-guided prostate biopsy brings reliability concerns due to the lack of contrast difference between prostate tissue and lesions. In this study, a novel hydraulic needle delivery system that is designed for performing magnetic resonance imaging (MRI)-guided prostate biopsy procedure with transperineal approach is introduced. The feasibility of the overall system was evaluated through in vitro phantom experiments under an MRI guidance. The in vitro experiments performed using a certified prostate phantom (incorporating MRI visible lesions). MRI experiments showed that overall hydraulic biopsy needle delivery system has excellent MRI compatibility (signal to noise ratio (SNR) loss < 3%), provides acceptable targeting accuracy (average 2.05±0.46 mm) and procedure time (average 40 min).

A novel fiber optic force sensor design with enhanced resolution through titanium coating is fabricated using Fabry-Pérot Interferometry (FPI) method and integrated into an 18 gauge MRI compatible biopsy needle, to be used in MRI guided interventional biopsy operations. The force sensor range and resolution are defined, and also needle insertion detection, deflection detection, tissue characterization and differentiation capabilities are tested via benchtop experiments. Overall system performance is tested via in vitro experiments under MRI using a commercial prostate phantom with representative leisons and it was shown that high resolution force sensing can help user to make sure that biopsy specimens are taken from the correct location. The fabricated sensor can measure forces up to 20 N with 0.1 N resolution and Ti coating enhances the sensor resolution to 0.03 N. Using biopsy needles with force measurement capability can improve the accuracy and safety of MRI guided minimally invasive biopsy procedures such as prostate biopsy. Biopsy needles incorporating high resolution force sensor can be used as a promising tool for cancer diagnosis thru stiffness detection of benign and malignant tissues instead of collecting biopsy specimens.

Objective: The objective of this paper is to introduce an acousto-optic optical fiber sensor for tracking catheter position during interventional magnetic resonance imaging (MRI) to overcome RF induced heating of active markers. Methods: The sensor uses a miniature coil coupled to a piezoelectric transducer, which is in turn mechanically connected to an optical fiber. The piezoelectric transducer converts the RF signal to acoustic waves in the optical fiber over a region including a fiber Bragg grating (FBG). The elastic waves in the fiber modulates the FBG geometry and hence the reflected light in the optical fiber. Since the coil is much smaller than the RF wavelength and the signal is transmitted on the dielectric optical fiber, the sensor effectively reduces RF induced heating risk. Proof of concept prototypes of the sensor are implemented using commercially available piezoelectric transducers and optical fibers with FBGs. The prototypes are characterized in a 1.5T MRI system in comparison with an active tracking marker. Results: Acousto-optical sensor shows linear response with flip angle and it can be used to detect signals from multiple coils for potential orientation detection. It has been successfully used to detect the position of a tacking coil in phantom in an imaging experiment. Conclusion: Acousto-optical sensing is demonstrated for tracking catheters during interventional MRI. Real-time operation of the sensor requires sensitivity improvements like using a narrow band FBG. Significance: Acousto-optics provides a compact solution to sense RF signals in MRI with dielectric transmission lines.

Günümüzde konjenital kalp hastalıklarının tedavisi sırasında kullanılan floroskopi gibi görüntüleme teknikleri, ileride oluşabilecek kanser riski sebebiyle özellikle pediatri için uygun değildir. Manyetik Rezonans Görüntüleme (MRG) iyonize radyasyon içermeyen çalışma prensibi, yumuşak dokuları daha iyi görüntüleme özelliği ve gerçek zamanlı fonksiyonel ölçüm avantajı sayesinde X ışını kullanılan görüntüleme tekniklerine etkili bir alternatif oluşturmaktadır. Bu çalışmada MRG uyumlu, MRG sistemi altında takip edilebilen ve özellikle doğuştan kalp hastalığı olan pediatrik hastalar için girişimsel prosedürlerde kullanılan düşük profilli RF (Radyo frekans) rezonans işaretleyicilere sahip yarı aktif kılavuz kateter tasarlanmıştır. RF rezonans işaretleyici bileşenlerinin geleneksel yöntemlerden farklı olarak ince film tabanlı düşük profillerde oluşturulması yeni bir üretim yaklaşımı olarak sunulmuştur. 5 Fr (1,67 mm) biyouyumlu kılavuz kateter şaftına entegre edilen RF rezonans işaretleyicilerin 1,5 T MRG sistemi altında görünürlükleri doğrulanmıştır. RF rezonans işaretleyici içeren kılavuz kateterin MRG altındaki RF ısınma testleri ASTM F2182 – 11a standardına uygun olarak yapılmıştır. En kötü koşulda dahi 0,25 ⁰C ısınma gözlemlenmiştir. Ayrıca RF rezonans işaretleyicilerin tasarımı ve üretimi aşamalarını hızlandırabilmek için sonlu eleman analiz yazılım programı (Comsol) kullanılarak simülasyon çalışmaları yapılmıştır. Uygulanan yöntem MRG uyumlu ve güvenli girişimsel kateter, alet ve cihazların üretimini mümkün hale getirmektedir.

Objectives A new microfabrication method to produce low profile radio frequency (RF) resonant markers on catheter shafts was developed. A semi-active RF resonant marker incorporating a solenoid and a plate capacitor was constructed on the distal shaft of a 5 Fr guiding catheter. The resulting device can be used for interventional cardiovascular MRI procedures. Materials and methods Unlike current semi-active device visualization techniques that require rigid and bulky analog circuit components (capacitor and solenoid), we fabricated a low profile RF resonant marker directly on guiding the catheter surface by thin film metal deposition and electroplating processes using a modified physical vapor deposition system. Results The increase of the overall device profile thickness caused by the semi-active RF resonant marker (130 µm thick) was lowered by a factor of 4.6 compared with using the thinnest commercial non-magnetic and rigid circuit components (600 µm thick). Moreover, adequate visibility performance of the RF resonant marker in different orientations and overall RF safety were confirmed through in vitro experiments under MRI successfully. Conclusion The developed RF resonant marker on a clinical grade 5 Fr guiding catheter will enable several interventional congenital heart disease treatment procedures under MRI.