High Intensity Focused Ultrasound (20 MHz) and Cryotherapy as Therapeutic Options for Granuloma Annulare and Other Inflammatory Skin Conditions

INTRODUCTION

In dermatology, inflammatory skin conditions impose a substantial burden worldwide, with existing therapies showing limited efficacy and side effects. This report aims to compare a novel immunological activation induced by hyperthermic 20 MHz high intensity focused ultrasound (HIFU) with conventional cryotherapy. The bioeffects from the two methods are initially investigated by numerical models, and subsequently compared to clinical observations after treatment of a patient with the inflammatory disease granuloma annulare (GA).

METHODS

Clinical responses to moderate energy HIFU and cryotherapy were analysed using numerical models. HIFU-induced pressure and heat transfer were calculated, and a three-layer finite element model simulated temperature distribution and necrotic volume in the skin. Model output was compared to 22 lesions treated with HIFU and 10 with cryotherapy in a patient with GA.

RESULTS

Cryotherapy produced a necrotic volume of 138.5 mm3 at - 92.7 °C. HIFU at 0.3-0.6 J/exposure and focal depths of 0.8 or 1.3 mm generated necrotic volumes up to only 15.99 mm3 at temperatures of 68.3-81.2 °C. HIFU achieved full or partial resolution in all treated areas, confirming its hyperthermic immunological activation effect, while cryotherapy also resolved lesions but led to scarring and dyspigmentation.

CONCLUSION

Hyperthermic immunological activation of 20 MHz HIFU shows promise for treating inflammatory skin conditions as exemplified by GA. Numerical models demonstrate minimal skin necrosis compared to cryotherapy. Suggested optimal HIFU parameters are 1.3 mm focal depth, 0.4-0.5 J/exposure, 1 mm spacing, and 1 mm margin. Further studies on GA and other inflammatory diseases are recommended.

Healing Process after High-Intensity Focused Ultrasound Treatment of Benign Skin Lesions: Dermoscopic Analysis and Treatment Guidelines

Background: High-Intensity Focused Ultrasound (HIFU) has emerged as a precise and non-invasive modality for tissue ablation and healing. This study presents a detailed dermoscopic analysis of skin healing post-High-Intensity Focused Ultrasound (HIFU) treatment, focusing on common benign skin lesions, such as seborrheic keratosis, sebaceous hyperplasia, vascular lesions, and sebaceous nevi. Methods: Prior to HIFU treatment, a comprehensive assessment was conducted, integrating ultrasound scanning and clinical evaluations. The TOOsonix System ONE-M was employed for HIFU treatments, with parameters tailored to each lesion type. Results: A common pattern observed across all lesions includes initial whitening post treatment, followed by scab formation and the development of a pink area with reparative vessels. This study, however, highlights distinct differences in fibrosis patterns and healing timelines across different lesion types. Each lesion type exhibited unique fibrosis patterns post treatment. Flatter variants of seborrheic keratosis healed within a month, displaying hypopigmentation and reparative vessels, alongside a distinct lattice fibrosis pattern in more verrucous forms, which took about two months to heal. Sebaceous hyperplasia, characterized by rapid healing within three weeks, demonstrated fibrosis with pink areas and perpendicular white lines, concluding with a slight depression. Vascular lesions varied in healing time based on depth, with superficial ones showing whitening and crust formation, while deeper lesions had vessel occlusion and size reduction accompanied by concentric fibrotic bands. Sebaceous nevi presented the longest healing duration of three months, characterized by amorphous white-gray structures, scab formation, and the emergence of pink areas with branching vessels, leading to clear skin with reduced white lines. Conclusions: in conclusion, this meticulous clinical evaluation highlights the unique healing characteristics and timelines for each skin lesion type treated with HIFU. These insights are invaluable for optimizing follow-up assessments, identifying potential complications, and refining treatment protocols. By providing detailed insights into the healing timelines and patterns for different types of lesions, patients can be better informed about their post-treatment journey.

Head-to-Head Comparison of Acoustic Properties of Lead-Free and PZT-Based HIFU Transducers Operating at 12 MHz

A direct comparison of performance and acoustic properties of high-intensity focused ultrasonic transducers utilizing lead-free (sodium bismuth titanate-NBT) and lead-based (lead zirconate titanate-PZT) piezoceramics is discussed. All transducers operate at 12 MHz at third harmonic frequency, having an outer diameter of 20 mm, a central hole of 5 mm in diameter, and a radius of curvature of 15 mm. The electroacoustic efficiency determined by a radiation force balance is evaluated in a range of input power levels up to 15 W. Schlieren tomography as well as hydrophone measurements are used for evaluation of the acoustic field distribution. It is found that the average electroacoustic efficiency of NBT-based transducers is approximately 40%, while it is around 80% in the PZT-based devices. NBT devices show significantly higher inhomogeneity of the acoustic field under schlieren tomography compared to PZT devices. From pressure measurements in the prefocal plane, it was found that the inhomogeneity could be attributed to depoling of significant areas of the NBT piezo-component during the fabrication process. In conclusion, PZT-based devices performed significantly better than those using lead-free material. However, the NBT devices show promise for this application and their electroacoustic efficiency as well as the uniformity of the acoustic field could be improved by employing a low-temperature fabrication process or repoling after processing.

High-Frequency (20 MHz) Focused Ultrasound: A Novel Method for Noninvasive Tattoo Removal

Alternatives or complements to laser tattoo removal are needed. Laser removal requires 8-12 sessions and can easily take longer than a year. Some colors cannot be removed, and scars may appear. Applied to allergic reactions in red tattoos, lasers can boost the allergy. A recently developed 20 MHz high-intensity focused ultrasound (HIFU) is introduced as a complementary method to lasers, but also as a stand-alone treatment for selected groups. 20 MHz HIFU allows for application of high-power ultrasound energy to very small focal targets in the dermis, and thereby precise confinement of thermal lesions in the outer layers of human skin, precisely where tattoo inks are deposited. HIFU treatment is "color blind" and can target any type of colored pigment in the dermis. It produces a controlled thermal lesion (up to 65°C) with superficial necrosis followed by an eschar with embedded tattoo pigment. This eschar, containing the tattoo pigment, is discharged over some weeks, and finally replaced by healed skin. HIFU can efficiently remove tattoos of any color in only 1-3 sessions. It can be applied to tattoos when lasers fail to produce efficient removal. The types of side effects are the same as with lasers. The operator shall be trained and knowledgeable. 20 MHz HIFU can furthermore be used in clinical and esthetic dermatology for various other applications, and a range of applications are open in clinical dermatology.

Treatment of Cutaneous Neurofibromas in Patients with Neurofibromatosis Type 1

Neurofibromatosis type 1 is a genetic disorder impacting approximately 2.5 million people worldwide, often leading to development of numerous benign yet disfiguring cutaneous neurofibromas (cNF). Removal of cNF is limited to excision or laser ablation with common post-operation complications and scarring. The current case explores a new approach to removal or reduction of cNF by a minimally invasive and pain-reduced treatment modality. A 40-year-old female patient with numerous cNF across her body underwent a single treatment using a 20 MHz dermatologically focused ultrasound device on seven selected cNF on the upper back. Each cNF was treated in a single session of 20-60 s without anesthesia due to manageable pain. Only one minimal adverse reaction in the form of dyspigmentation in a single treated tumor was noted from treatment or during the healing of a thin scab that formed on each cNF a few days after treatment. At the 12-month follow-up, four out of seven treated cNF showed full remission, two showed partial or significant reduction in tumor volume, while two did not respond to treatment. The reason for the variability is not fully understood, but speculations include difference in tissue content, e.g., due to tumor age. The method is concluded to be a promising candidate for a new safe and minimally invasive treatment that can potentially be used for single-session removal/reduction of a large number of cNF. Further research should focus on refining treatment parameters and strategies to enhance response predictability.

Lead-Free HIFU Transducers

High-intensity focused ultrasound transducers operating at 4 MHz based on lead-free piezoceramics from the sodium bismuth titanate (NBT) family are described. First, the piezoelectric material (Pz12X) is evaluated from the standpoint of transducer design and its important characteristics, including temperature dependance of several parameters such as dielectric and mechanical coefficients. Then, the performance of six transducers of the same design is evaluated in terms of electro-acoustic efficiency and its dependency on the operating acoustic power level up to 30 W. Overall, the initial electro-acoustic efficiency of three independent transducers is approximately 50% at low acoustic power levels and slightly drops down to 42% as the input electric power reaches 10 W. This process is stable and fully reversible. Moreover, the stability of electro-acoustic efficiency over extended power burst cycling is studied using another two transducers up to 95 × 10³ power bursts of 250-ms duration and acoustic power of 10 W. This protocol is beyond the typical clinical use of similar devices in practice. No significant changes in electro-acoustic performance are noted. Additionally, the input electric power and the output acoustic power, together with the temperature of the piezoelectric component, are evaluated simultaneously over the period of one power burst. It is found that the maximum operating temperature over a high-input electric power burst of 600 J is below 60°C, which defines the operational limit for such devices, as the de-poling temperature of the lead-free material is around 85°C. It is found that the lead-free material from the NBT family is also a promising alternative to lead-based PZT-type materials in high-power therapeutic ultrasound.

Treatment of Condylomata Acuminata Using a New Non-Vapor-Generating Focused Ultrasound Method following Imiquimod 5% Cream

Condylomata acuminata is the most common sexually transmitted disease in the world. Physical treatments include excision, cryotherapy, electrocautery and ablative CO₂, and Nd:YAG laser ablation, while topical treatments include imiquimod immunotherapy and antimitotic podophyllotoxin or sinecatechins. Efficacies of all methods are low, and recurrences are very common. A new combined method is presented as a single case in a 25-year-old male patient diagnosed with numerous condylomas on the penis, scrotum, and lower abdomen. The treatment consisted of a 7-week topical monotherapy using 5% imiquimod cream followed by local treatment with 20 MHz high-intensity focused ultrasound on remaining recalcitrant lesions. Results showed resolution of approximately 70% of the condylomas after imiquimod treatment, and full resolution of all recalcitrant condylomas treated subsequently with high-intensity focused ultrasound. The method is concluded to be safe and effective and, furthermore, presents a new physical method that does not generate airborne infectious human papillomavirus particles that pose a health risk for the medical team performing therapy. Further studies in larger populations are recommended to confirm the combined efficacy of the proposed method.

Strongly Focused HIFU Transducers With Simultaneous Optical Observation for Treatment of Skin at 20 MHz

High-intensity focused ultrasound (HIFU) transducers are proposed as a new treatment modality for dermatology. The shape and size of pressure fields generated by strongly focused transducers with an f-number equal to 0.75 operating at frequencies up to 20 MHz are analyzed analytically using the Lucas-Muir model and numerically with the wide-angle Khokhlov-Zabolotskaya-Kuznetsov method. The modeling results under quasi-linear conditions are compared against measurements performed in an acoustic tank with the aid of a fiberoptic hydrophone. The size of the focal zone expressed by their depth of focus and focal diameter is found to be directly controlled by their operating frequency and f-number. Devices manufactured for an operating frequency of 20 MHz are characterized by their 6 dB depth of focus of 490 μm and focal diameter of 80.6 µm. The devices are further studied at high power levels using a polyacrylic tissue-mimicking phantom. The devices are equipped with an optical observation system allowing simultaneous treatment and observation of the skin surface. In comparison to conventional cosmetic applications of HIFU, the devices analyzed are concluded to be ideal for treatment of precisely selected and confined layers of the human skin.

Treatment of Seborrheic Keratosis by High Frequency Focused Ultrasound - An Early Experience with 11 Consecutive Cases

PURPOSE

High intensity focused ultrasound operating at 20 MHz has been demonstrated as a safe and efficient treatment modality for a range of dermatological indications. The method is potentially also applicable to removal of seborrheic keratosis.

PATIENTS AND METHODS

A total of 54 seborrheic keratoses in 11 volunteer subjects (8 women and 3 men, average age 51.5 ± 13.2 years) were treated in a single session with a medical 20 MHz high intensity focused ultrasound device developed for dermatological conditions. Handpieces with nominal focal depths of 0.8 mm below the skin surface were used to administer acoustic energy of 0.99-1.2 J/dose. An integrated dermoscope in the handpiece was used to monitor the treatment in real-time. Treatment efficacy and side-effects were assessed directly after treatment and at follow-up 4-15 weeks after treatment.

RESULTS

The treatment showed positive results in 96.3% of the cases. About 68.5% of the cases were classified as complete response and 27.8% of the cases as partial response. Two cases (3.7%) did not respond to treatment and were classified as stable condition. No subjects experienced worsening of their condition, and no treatment received the classification of progressive condition. Side effects were primarily redness in the treatment area due to superficial telangiectasia, mild scarring, and persisting and slow-healing lichen planus-like keratosis. No adverse events were observed.

CONCLUSION

HIFU is concluded to be a safe and efficient skin treatment for seborrheic keratoses. It has advantages over conventional treatments that can lead to pain during treatment and scarring after healing.

Treatment of superficial benign vascular tumors by high intensity focused ultrasound: Observations in two illustrative cases

Background

Existing therapeutic methods for reduction or removal of superficial vascular malformations and tumors have high risks of scarring and other complications that result in aesthetic appearance less favorable than the baseline. Patients are often cautioned against intervention, which can lead to psychosocial problems and low self‐esteem. Improved treatment modalities are therefore relevant from both medical and aesthetic perspectives.

Methods

Two volunteer subjects were treated with a medical 20 MHz high intensity focused ultrasound device developed for dermatological conditions. One patient was given three treatments to remove a superficial congenital hemangioma on the left middle cheek. The other patient was given a single treatment to remove seven cherry angiomas on the thighs. Handpieces with nominal focal depths of 0.8 – 1.8 mm below the skin surface were used to administer acoustic energy of 1.1 – 1.2 J/dose. An integrated dermoscope in the handpiece was used to monitor the treatment in real‐time.

Results

During treatment, blood in the capillary network of the lesions was coagulated immediately, and capillary walls were collapsed due to the thermal and mechanical effects of the high intensity focused ultrasound. During the healing phase, the areas regenerated a normal skin structure with very limited scar or dyspigmentation. At follow‐up, a clear aesthetic improvement was observed over the baseline for all treated targets with the exception of two cherry angiomas, where focal depth and/or dose coverage had not been optimal.

Conclusion

High intensity focused ultrasound is concluded to be a safe and efficient skin treatment for benign superficial vascular malformations and tumors.

Removal of Common Warts by High-Intensity Focused Ultrasound: An Introductory Observation

Therapies of common warts are cumbersome and not very effective. Recurrences are common. A new 20 MHz high-intensity focused ultrasound (HIFU) method is introduced as a new potential treatment modality. With HIFU, selected targets in the epidermis and dermis can be treated with full control of the depth and position of the ultrasound lesion and the energy applied to the target. The treatment can be monitored directly in real-time via an integrated dermoscope in the ultrasound probe. Two warts were treated with 8-10 shoulder-by-shoulder treatment doses, focal depth 1.3 mm, and 1.2 J/dose. Pretreatment ultrasound B-mode scanning had shown the thickness and depth of the warts. The treated areas developed a dry wound covered by a crust over the next 1-2 days. After 2 weeks the skin was healed, with no wart and no scar. Observation showed no reoccurrence. HIFU has future potential for treatment of common warts and flat warts, and a broad range of skin lesions being logic further candidates for targeted ablative treatment. One single treatment may suffice. It is, therefore, a new modality in dermatology with a large range of indications.

High-frequency (20 MHz) high-intensity focused ultrasound: New ablative method for color-independent tattoo removal in 1-3 sessions. An open-label exploratory study

BACKGROUND

High-intensity focused ultrasound (HIFU) operating at 20 MHz is new and potentially applicable to ablative tattoo removal. The method was documented safe and rational in preclinical testing.

MATERIALS AND METHODS

High-intensity focused ultrasound was introduced to subjects when lasers and dermatome shaving had failed or caused side effects. Transducers with focal depths between 1.1 mm and 1.7 mm in the skin were used, and settings of 0.4-1.2 J/shot at pulse durations of 150 ms were applied. Tattoos were covered with synergistic "shoulder-by-shoulder" focused ultrasound shots. Effectiveness and side effects were measured.

RESULTS

Twenty-two subjects with 67 tattoos were treated. 62% benefitted (19% cleared, 43% partially cleared), and 28% had minor effect. VAS pain was 5-6 versus 7-9 with previous lasers removal. Wound healing was longer after HIFU ablation (1-3 months). 57% of subjects had no scar or minor visible changes of skin surface markings only, while 19% had moderate or major skin thickening. Hypertrophic scar or keloid scars were not observed.

DISCUSSION/CONCLUSION

High-intensity focused ultrasound was effective in removal of difficult tattoos of any color where Nd:YAG lasers had failed. The method only needs 1-3 sessions. As an ablative method, the wound healing period is longer than with laser removal and needs attention. Focused ultrasound can be used as a first-line treatment of smaller tattoos independent of color, and second line when Nd:YAG lasers have failed or caused problems. The operator shall be qualified, as with lasers.

High-frequency (20 MHz) high-intensity focused ultrasound: New Treatment of actinic keratosis, basal cell carcinoma, and Kaposi sarcoma. An open-label exploratory study

Background

Skin cancer is common, growing, challenging, and in need of progress in early‐stage treatment. 20 MHz high‐intensity focused ultrasound (HIFU) is new and applied to actinic keratosis (AK) and skin cancers for the first time. HIFU of lower frequency is already used in the treatment of internal cancers.

Materials and Methods

Eight patients with 201 AK lesions, one patient with 7 basal cell carcinomas (reoccurrences after PDT), and one patient with 7 Kaposi sarcoma lesions (4 treated with radiotherapy in the past) were given 1‐3 HIFU treatments. Twenty megahertz HIFU was dosed as 150 ms at 0.6‐1.2 J/shot applied to target lesions. Probes with different target depths were available. The preferred shot energy and focal depth in AK were 0.9 J and 1.3 mm. A “Sandwich” strategy with HIFU applied in two depths were tried in cancers. The follow‐up period was 3‐6 months.

Results

All AK cleared except 5, giving a cure rate of 97%. Post‐treatment lesion healed in 1‐2 weeks with no scar. VAS pain was from 1 to 8, and in any case less than experienced with previous PDT. In both basal cell carcinoma (BCC) and sarcoma, healing was confirmed by histological verification.

Discussion/conclusion

20 MHz HIFU was an effective and safe treatment of AK. This new treatment, applicable to any anatomical site, has promising advantages relative to PDT and has the potential to replace or supplement PDT in future. Case‐observations indicated that HIFU can be useful in skin cancers as well.

High-frequency (20 MHz) high-intensity focused ultrasound system for dermal intervention: A 12-week local tolerance study in minipigs

BACKGROUND

High-intensity focused ultrasound (HIFU) operating at 20 MHz is new and applicable to skin. Details of use and instrumentation are not documented.

MATERIALS AND METHODS

A GLP compliant 12-week study of Göttingen minipigs (n = 3) was undertaken. Effects of HIFU treatment at different focal depths, energy levels and field size (single shot vs 5 × 5 multiple shots) were studied. Clinical scoring and histology of treated sites were made.

RESULTS

High-intensity focused ultrasound showed instant and initial effects with wheal and flare responses followed by delayed inflammatory reactions associated with outer skin necrosis, depending on energy dose. HIFU treatment was tunable in the range 0.3-1.5 J, ablative at higher energy level. Transducers with deeper focal points gave more profound effects, while epidermal effects were comparable. Multiple doses of 5 × 5 shots produced stronger reactions than single dose indicating that nearby applied shots were synergistic. Recovery from single doses was faster than in multidose areas. Clinical scarring at the end point was not seen despite occasional fibrous change of dermis. Findings illustrated intended therapeutic use; no special safety issues of concern were raised.

CONCLUSION

The new 20 MHz HIFU was reproducible, tunable and produced targeted effects in the outer skin, for example instant wheal and flare followed by inflammation and possibly necrosis depending on energy setting. Reactions recovered during the study with only minor findings at study end. No special safety concerns were raised. The method can be controlled and modulated, and it is ready for clinical testing of dermatological disease indications including conditions presently treated with lasers.

High-frequency (20-MHz) high-intensity focused ultrasound (HIFU) system for dermal intervention: Preclinical evaluation in skin equivalents

BACKGROUND

High-intensity focused ultrasound (HIFU) for non-invasive treatment of a range of internal pathologies including cancers of major organs and cerebral pathologies is in exponential growth. Systems, however, operate at relatively low frequencies, in the range of 200-2000 kHz as required for deep axial penetration of the body. HIFU utilizing frequencies in excess of 15 MHz has so far not been explored, but presents an opportunity to extend the HIFU modality to target specific dermal lesions and small animal research.

MATERIALS AND METHODS

A new 20-MHz HIFU system (TOOsonix ONE-R) with narrow focus corresponding to the dermis was studied in acoustic skin equivalents, for example, in a tissue-mimicking gel and in bovine liver. HIFU lesion geometry, depth, and diameter were determined. The temperature increase in the focal point was measured as a function of acoustic power and the duration of HIFU exposure.

RESULTS

The system produces highly reproducible ultrasound lesions with predictable and configurable depths of 1-2 mm, thus corresponding to the depth of the human dermis. The lesion geometry was elongated triangular and sized 0.1-0.5 mm, convergent to a focal point skin deep. Focal point temperature ranged between 40 and 90°C depending on the chosen setting. Observations were confirmed ex vivo in bovine liver and porcine muscle. Variation of acoustic power and duration of exposure produced linear effects in the range of the settings studied. Thus, effects could be adjusted within the temperature interval and spatial field relevant for clinical therapy and experimental intervention targeting the dermal layer of human skin.

CONCLUSION

The tested 20-MHz HIFU system for dermal applications fulfilled key prerequisite of narrow-field HIFU dedicated to cutaneous applications regarding reproducibility, geometry, and small size of the applied ultrasound lesions. Controlled adjustment of acoustic lesions within the temperature range 40-90°C qualifies the system for a range of non-ablative and ablative applications in dermatological therapy.

Characterization of Kerfless Linear Arrays Based on PZT Thick Film

Multielement transducers enabling novel cost-effective fabrication of imaging arrays for medical applications have been presented earlier. Due to the favorable low lateral coupling of the screen-printed PZT, the elements can be defined by the top electrode pattern only, leading to a kerfless design with low crosstalk between the elements. The thick-film-based linear arrays have proved to be compatible with a commercial ultrasonic scanner and to support linear array beamforming as well as phased array beamforming. The main objective of the presented work is to investigate the performance of the devices at the transducer level by extensive measurements of the test structures. The arrays have been characterized by several different measurement techniques. First, electrical impedance measurements on several elements in air and liquid have been conducted in order to support material parameter identification using the Krimholtz-Leedom-Matthaei model. It has been found that electromechanical coupling is at the level of 35%. The arrays have also been characterized by a pulse-echo system. The measured sensitivity is around -60 dB, and the fractional bandwidth is close to 60%, while the center frequency is about 12 MHz over the whole array. Finally, laser interferometry measurements have been conducted indicating very good displacement level as well as pressure. The in-depth characterization of the array structure has given insight into the performance parameters for the array based on PZT thick film, and the obtained information will be used to optimize the key parameters for the next generation of cost-effective arrays based on piezoelectric thick film.

Effectiveness and Safety Assessment of Citrate Anticoagulation During Albumin Dialysis in Comparison to Other Methods of Anticoagulation

Liver failure is a serious and often deadly disease often requiring MARS (Molecular Adsorbent Recirculating System) therapy. Choosing the safe and effective method of anticoagulation during artificial liver support systems seems to be very difficult and extremely important. The aim of this study was to assess effectiveness and safety of regional anticoagulation with citrate in liver failure patients during MARS. We used a single center observational study. We analyzed 158 MARS sessions performed in 65 patients: 105 (66.5%) sessions in 41 patients with heparin anticoagulation, 40 (25.3%) sessions in 19 patients with citrate, and 13 (8%) sessions in only five patients without anticoagulation, that were excluded from part of the analysis. To determine the effectiveness of regional anticoagulation with citrate, probability of filter survival and changes in laboratory parameters were analyzed according to the applied method of anticoagulation. The safety of citrate was determined by Ca/Ca²⁺ ratio, acid-base balance, bleeding complications, and the need for blood product transfusions. The probability of filter survival in the citrate group was 94% and in the heparin group 82% (P = 0.204). There was no relationship between the method of anticoagulation and effectiveness of MARS therapy in lowering the levels of the analyzed parameters. Only one patient had a Ca/Ca²⁺ ratio higher than he safety margin. There were no statistically significant changes in pH and lactate level irrespective of anticoagulation; bicarbonate dropped significantly only in the heparin group (P = 0.03). The frequency of bleeding complications and the need for transfusions did not differ significantly between groups. Regional anticoagulation with citrate can be an effective and safe method of anticoagulation during MARS therapy, but requires attentive monitoring and further studies in liver failure patients.

Utility of transthoracic echocardiography (TTE) in assessing fluid responsiveness in critically ill patients - a challenge for the bedside sonographer

Transthoracic echocardiography (TTE) has become one of the most important diagnostic tools in the treatment of critically ill patients. It allows clinicians to recognise potentially reversible life-threatening situations and is also very effective in the monitoring of the fluid status of patients, slowly substituting invasive methods in the intensive care unit. Hemodynamic assessment is based on a few static and dynamic parameters. Dynamic parameters change during the respiratory cycle in mechanical ventilation and the level of this change directly corresponds to fluid responsiveness. Most of the parameters cannot be used in spontaneously breathing patients. For these patients the most important test is passive leg raising, which is a good substitute for fluid bolus. Although TTE is very useful in the critical care setting, we should not forget the important limitations, not only technical ones but also caused by the critical illness itself. Unfortunately, this method does not allow continuous monitoring and every change in the patient's condition requires repeated examination.

Development of Porous Piezoceramics for Medical and Sensor Applications

The use of porosity to modify the functional properties of piezoelectric ceramics is well known in the scientific literature as well as by the industry, and porous ceramic can be seen as a 2-phase composite. In the present work, examples are given of applications where controlled porosity is exploited in order to optimise the dielectric, piezoelectric and acoustic properties of the piezoceramics. For the optimisation efforts it is important to note that the thickness coupling coefficient k_t will be maximised for some non-zero value of the porosity that could be above 20%. On the other hand, with a good approximation, the acoustic velocity decreases linearly with increasing porosity, which is obviously also the case for the density. Consequently, the acoustic impedance shows a rather strong decrease with porosity, and in practice a reduction of more than 50% may be obtained for an engineered porous ceramic. The significance of the acoustic impedance is associated with the transmission of acoustic signals through the interface between the piezoceramic and some medium of propagation, but when the porous ceramic is used as a substrate for a piezoceramic thick film, the attenuation may be equally important. In the case of open porosity it is possible to introduce a liquid into the pores, and examples of modifying the properties in this way are given.

Dual-frequency transducer for nonlinear contrast agent imaging

Detection of high-order nonlinear components issued from microbubbles has emerged as a sensitive method for contrast agent imaging. Nevertheless, the detection of these high-frequency components, including the third, fourth, and fifth harmonics, remains challenging because of the lack of transducer sensitivity and bandwidth. In this context, we propose a new design of imaging transducer based on a simple fabrication process for high-frequency nonlinear imaging. The transducer is composed of two elements: the outer low-frequency (LF) element was centered at 4 MHz and used in transmit mode, whereas the inner high-frequency (HF) element centered at 14 MHz was used in receive mode. The center element was pad-printed using a lead zirconate titanate (PZT) paste. The outer element was molded using a commercial PZT, and curved porous unpoled PZT was used as backing. Each piezoelectric element was characterized to determine the electromechanical performance with thickness coupling factor around 45%. After the assembly of the two transducer elements, hydrophone measurements (electroacoustic responses and radiation patterns) were carried out and demonstrated a large bandwidth (70% at -3 dB) of the HF transducer. Finally, the transducer was evaluated for contrast agent imaging using contrast agent microbubbles. The results showed that harmonic components (up to the sixth harmonic) of the microbubbles were successfully detected. Moreover, images from a flow phantom were acquired and demonstrated the potential of the transducer for high-frequency nonlinear contrast imaging.

Fabrication of high-frequency pMUT arrays on silicon substrates

A novel technique based on silicon micromachining for fabrication of linear arrays of high-frequency piezoelectric micromachined ultrasound transducers (pMUT) is presented. Piezoelectric elements are formed by deposition of lead zirconia titanate into etched features of a silicon substrate such that the depth of these features determine the element thickness and hence the resonance frequency. The process leaves a near planar surface which is ideal for further wafer level processing such as top electrode and interconnect formation. A fabricated element is characterized by pulse echo response.