Giulia Frauenfelder

Magnetic resonance-based thermometry during laser ablation on ex-vivo swine pancreas and liver

Laser Ablation (LA) is a minimally-invasive procedure for tumor treatment. LA outcomes depend on the heat distribution inside tissues and require accurate temperature measurement during the procedure. Magnetic resonance imaging (MRI) allows a non-invasive and three-dimensional thermometry of the organ undergoing LA. In this study, the temperature distribution within two swine pancreases and three swine livers undergoing LA (Nd:YAG, power: 2 W, treatment time: 4 min) was monitored by a 1.5-T MR scanner, utilizing two T1-weighted sequences (IRTF and SRTF). The signal intensity in four regions of interest, placed at different distances from the laser applicator, was related to temperature variations monitored in the same regions by twelve fiber Bragg grating sensors. The relationship between the signal intensity and temperature increase was calculated to obtain the calibration curve and to evaluate accuracy, sensibility and precision of each sequence. This is the first study of MR-based thermometry during LA on pancreas. More specifically, the IRTF sequence provides the highest temperature sensitivity in both liver (1.8 ± 0.2 °C(-1)) and pancreas (1.8 ± 0.5 °C(-1)) and the lowest precision and accuracy. SRTF sequence on pancreas presents the highest accuracy and precision (MODSFRT = -0.1 °C and LOASFRT = [-2.3; 2.1] °C).

Error of a Temperature Probe for Cancer Ablation Monitoring Caused by Respiratory Movements: Ex Vivo and In Vivo Analysis

Hyperthermal techniques are spreading as an alternative to conventional surgery for cancer removal. A real-time temperature feedback can be used to adjust the treatment settings, in order to improve the clinical outcomes. In this paper, we experimentally assessed the feasibility for distributed temperature monitoring of a custom probe, which consists of a needle embedding six fiber Bragg gratings (FBGs). Since FBGs are also sensitive to strain, we focused on the analysis of the measurement error (artifact) caused by respiratory movements. We assessed the artifact both on ex vivo pig liver and lung (by mimicking the movement of these organs caused by respiration) and on in vivo trial on pig liver. Lastly, we proposed an algorithm to detect and minimize the artifact during ex vivo liver laser ablation. During both ex vivo and in vivo trials, the probe insertion within the organ was easy and safe. The artifact was significant (up to 3 °C), but the correction algorithm allows minimizing the error. The main advantages of the proposed probe are: 1) spatially resolved temperature monitoring (in six points of the tissue by inserting a single needle) and 2) the needle is magnetic resonance (MR)-compatible, hence can be used during MR-guided procedure. Even if the model is close to humans, further trials are required to investigate the feasibility of the probe for clinical applications.

Emerging clinical applications of computed tomography

X-ray computed tomography (CT) has recently been experiencing remarkable growth as a result of technological advances and new clinical applications. This paper reviews the essential physics of X-ray CT and its major components. Also reviewed are recent promising applications of CT, ie, CT-guided procedures, CT-based thermometry, photon-counting technology, hybrid PET-CT, use of ultrafast-high pitch scanners, and potential use of dual-energy CT for material differentiations. These promising solutions and a better knowledge of their potentialities should allow CT to be used in a safe and effective manner in several clinical applications.

Magnetic Resonance-compatible needle-like probe based on Bragg grating technology for measuring temperature during Laser Ablation

Temperature monitoring in tissue undergone Laser Ablation (LA) may be particularly beneficial to optimize treatment outcome. Among many techniques, fiber Bragg grating (FBG) sensors show valuable characteristics for temperature monitoring in this medical scenario: good sensitivity and accuracy, and immunity from electromagnetic interferences. Their main drawback is the sensitivity to strain, which can entail measurement error for respiratory and patient movements. The aims of this work are the design, the manufacturing and the characterization of a needle-like probe which houses 4 FBGs. Three FBGs have sensitive length of 1 mm and are used as temperature sensors; one FBG with length of 10 mm is used as reference and to sense eventual strain. The optical fiber housing the FBGs was encapsulated within a needle routinely used in clinical practice to perform MRI-guided biopsy. Two materials were used for the encapsulation: i) thermal paste for the 3 FBGs used for temperature monitoring, to maximize the thermal exchange with the needle; ii) epoxy resin for the reference FBG, to improve its sensitivity to strain. The static calibration of the needle-like probe was performed to estimate the thermal sensitivity of each FBG; the step response was investigated to estimate the response time. FBGs 1 mm long have thermal sensitivity of 0.01 nm·°C-1, whereas the reference FBG presents 0.02 nm·°C-1. For all FBGs, the response time was in the order of 100 ms. Lastly, experiments were performed on ex vivo swine liver undergoing LA to i) evaluate the possible presence of measurement artifact, due to the direct absorption of laser light by the needle and ii) assess the feasibility of the probe in a quasi clinical scenario.

Feasibility assessment of an FBG-based probe for distributed temperature measurements during laser ablation

During thermal procedures, the monitoring of tissue temperature is useful to improve therapy success. The aim of this study is the feasibility assessment of a Fiber Bragg Grating (FBG)-based probe, which contains six FBGs, to obtain distributed temperature measurement in tissue undergoing laser ablation (LA). Among different thermometric techniques, FBG sensors show valuable characteristics, even though their sensitivity to strain entails measurement error for patient respiratory movement. We performed: i) the static calibration of the FBG-based probe to estimate the thermal sensitivity of the six FBGs; ii) the estimation of the response time of the FBGs. All FBGs have a thermal sensitivity of 10 pm·°C-1 and a time constant in the order of <; 250 ms. Additionally, we performed a preliminary estimation of the error due to the strain and caused by respiratory movements. Experiments were carried out by simulating a typical respiratory movement on ex vivo swine liver. The measurement error was <;0.6 °C for all FBGs. Eventually, experiments were performed on ex vivo porcine liver undergoing LA to assess the measurement error, called artifact, caused by the direct absorption of the laser light by the metallic needle. The artifact was firstly investigated at 12 relative positions between the needle and the laser applicator, then corrected by a two-variables model. After adjustment, the artifact decreases from about 2.1 °C to about 0.1 °C. The solutions proposed in this study foster confirming the feasibility of the FBG-based probe for temperature monitoring in organ undergoing LA.

Percutaneous low-dose CT-guided lung biopsy with an augmented reality navigation system: validation of the technique on 496 suspected lesions

PURPOSE To validate a CT-navigation system during percutaneous lung biopsy (PLB). METHODS Four hundred-ninety-six patients underwent low-dose CT-guided PLB. Lesion diameter (LD), procedural time (PT), histologic validity, lesion distance from pleural surface (DPS), needle distance travelled during procedure (DTP), complications and radiation exposure were recorded. RESULTS Hysto-patological diagnosis was obtained in 96.2% cases. Mean PT, DPS, DTP, LD were respectively 29.5min, 12.4mm, 17.9mm, 20.7mm. In cases of major complications (4.6%), higher values of DTP were measured. CONCLUSIONS CT-navigation system allowed a good success in terms of diagnosis in small lesions and when a long DTP is required.

Successful endovascular embolization of an intralobar pulmonary sequestration

Pulmonary sequestration is a congenital malformation characterized by dysplastic pulmonary tissue which receives blood supply by arterial systemic system, not in communication with tracheobronchial tree. Although it could be asymptomatic, it can also cause recurrent infections and hemoptysis, rarely massive and fatal. The conventional treatment consists in surgical resection of the pulmonary sequestration, but in the last few years endovascular embolization has been proposed as a valid therapeutic alternative. In this paper, we report the case of a 43–year-old woman affected by recurrent hemoptysis. Computed tomography angiography of the chest, abdomen, and pelvis was performed in emergency setting. Intralobar pulmonary sequestration in the lower lobe of the right lung was found. A bulky aberrant artery originating from the thoracic aorta supplied the pulmonary sequestration. The interventional radiologist performed an endovascular embolization with coils of the vascular malformation. The technical success of the procedure was confirmed by computed tomography angiography of the chest performed on the fourth day after procedure. Further examination performed 6 months later showed no complications. The patient was completely asymptomatic during follow-up. This procedure can demonstrate that arterial embolization is a valid and effective therapeutic alternative to surgical resection in the treatment of pulmonary sequestration.

Interventions and Therapy in Rheumatology

Patients affected by rheumatic conditions frequently present with spine degeneration and vertebral compression fractures, mainly related to the long-term therapies with glucocorticosteroids. A mini-invasive approach provided by interventional radiology techniques, especially vertebroplasty, plays a relevant role in the pain management of these patients; vertebroplasty represents the symptomatic treatment of fracture pain, so patients must always be included in a specific therapeutic workup of the rheumatic condition. This article describes patient selection criteria, technique, and outcomes of vertebroplasty in patients affected by rheumatic disease and secondary osteoporosis caused by glucocorticosteroids.

Temperature monitoring during radiofrequency ablation of liver: In vivo trials

Radiofrequency ablation (RFA) is a minimally invasive procedure used to treat tumors by means of hyperthermia, mostly through percutaneous approach. The tissue temperature plays a pivotal role in the achievement of the target volume heating, while sparing the surrounding healthy tissue from thermal damage. Several techniques for thermometry during RFA are investigated, most of them based on the use of single-point measurement system (e.g., thermocouples). The measurement of temperature map is crucial for the real-time control and fine adjustment of the treatment settings, to optimize the shape and size of the ablated volume. The recent interest about fiber optic sensors and, among them, fiber Bragg gratings (FBGs) for the monitoring of thermal effects motivated further investigation. In particular, the feature of FBGs to form an array of several elements, thus to be inscribed within the same fiber, allows the use of a single probe for the multi-points monitoring of the tissue temperature during RFA. Hence, the aim of this study is the development and characterization of a needle-like probe embedding an array of three FBGs, which was tested on pig liver during in vivo trials. The needle allows a safe and easy insertion of the fiber optic within the liver. It was inserted by ultrasound guidance into the liver, and monitored the change of tissue temperature during RFA controlled by the roll-off technique. Also the measurement error induced by breathing movements of the liver was assessed (less than 3 °C). Results encourage the use of the probe in clinical settings, as well as the improvement of some features, e.g., a higher number of FBGs for performing quasi-distributed measurement.Radiofrequency ablation (RFA) is a minimally invasive procedure used to treat tumors by means of hyperthermia, mostly through percutaneous approach. The tissue temperature plays a pivotal role in the achievement of the target volume heating, while sparing the surrounding healthy tissue from thermal damage. Several techniques for thermometry during RFA are investigated, most of them based on the use of single-point measurement system (e.g., thermocouples). The measurement of temperature map is crucial for the real-time control and fine adjustment of the treatment settings, to optimize the shape and size of the ablated volume. The recent interest about fiber optic sensors and, among them, fiber Bragg gratings (FBGs) for the monitoring of thermal effects motivated further investigation. In particular, the feature of FBGs to form an array of several elements, thus to be inscribed within the same fiber, allows the use of a single probe for the multi-points monitoring of the tissue temperature during RFA. Hence, the aim of this study is the development and characterization of a needle-like probe embedding an array of three FBGs, which was tested on pig liver during in vivo trials. The needle allows a safe and easy insertion of the fiber optic within the liver. It was inserted by ultrasound guidance into the liver, and monitored the change of tissue temperature during RFA controlled by the roll-off technique. Also the measurement error induced by breathing movements of the liver was assessed (less than 3 °C). Results encourage the use of the probe in clinical settings, as well as the improvement of some features, e.g., a higher number of FBGs for performing quasi-distributed measurement.

Feasibility assessment of CT-based thermometry for temperature monitoring during thermal procedure: Influence of ROI size and scan setting on metrological properties.

Computed tomography (CT) thermometry belongs to the wide class of non-invasive temperature monitoring techniques, which includes ultrasound and Magnetic Resonance thermometry. Non-invasive techniques are particularly attractive to be used in hyperthermal procedures for their ability to produce a three-dimensional temperature map and because they overcome the risks related to the insertion of sensing elements.