Radiofrequency Volume Research Articles

Miniaturized MR-compatible ultrasound system for real-time monitoring of acoustic effects in mice using high-resolution MRI

Visualization of focused ultrasound in high spatial and temporal resolution is crucial for accurately and precisely targeting brain regions noninvasively. Magnetic resonance imaging (MRI) is the most widely used noninvasive tool for whole-brain imaging. However, focused ultrasound studies employing high-resolution (> 9.4 T) MRI in small animals are limited by the small size of the radiofrequency (RF) volume coil and the noise sensitivity of the image to external systems such as bulky ultrasound transducers. This technical note reports a miniaturized ultrasound transducer system packaged directly above a mouse brain for monitoring ultrasound-induced effects using high-resolution 9.4 T MRI. Our miniaturized system integrates MR-compatible materials with electromagnetic (EM) noise reduction techniques to demonstrate echo-planar imaging (EPI) signal changes in the mouse brain at various ultrasound acoustic intensities. The proposed ultrasound-MRI system will enable extensive research in the expanding field of ultrasound therapeutics.

A multimodal axial array resonator and its application in radiofrequency (RF) volume coil designs for low-field open magnetic resonance imaging (MRI)

A multimodal axial array resonator and its application in radiofrequency (RF) volume coil designs for low-field open magnetic resonance imaging (MRI)

Comparison of Endoscopic Partial Inferior Turbinectomy, Submucosal Radiofrequency Volume Reduction and Inferior Turbinoplasty in Patients with Hypertrophied Inferior Turbinates

AbstractBackground: Chronic nasal obstruction is a global health problem affecting large number of population all over the world. Hypertrophy of the Inferior Turbinates (HIT) is one of the leading causes of nasal obstruction. There is no con-sensus for best method of inferior turbinate volume reduction.Objective: To compare between the endoscopic Partial Inferior Turbinectomy (PIT), Radiofrequency Assisted Tur-binate volume Reduction (RATR) and submucosal resection (SMR) of the inferior turbinate in success of turbinate size reduction with preservation of the physiological functions of the inferior turbinate.Study Design and Setting: A prospective randomized clinical trial in a tertiary care center.Patients and Methods: 150 patients diagnosed to have (HIT) were randomly selected and allocated into 3 groups for the 3 treatment options. The patients were evaluated pre-operatively and post-operatively by a modified Arabic trans-lation of the Sino-Nasal Outcome Test (MA-SNOT16 test) and rigid nasal endoscopy. A p-value of less than 0.001 was considered statistically significant.Results: There was statistically significant improvement in MA-SNOT16 score post-operatively in all groups which continued to be improved more in SMR group. Least operative time was in RATR group and more crustations. Slightly better long term follow-up was observed in SMR group.Conclusion: There is no consensus on one surgical tech-nique for the inferior turbinate volume reduction. Still there is a need for systematic reviews and meta-analysis to reach the best option.

Quantification of N-Acetyl Aspartyl Glutamate in Human Brain using Proton Magnetic Resonance Spectroscopy at 7 T

UDC 543.422.25:611.81 The separation of N-acetyl aspartyl glutamate (NAAG) from N-acetyl aspartate (NAA) and other metabolites, such as glutamate, by in vivo proton magnetic resonance spectroscopy at 7 T is described. This method is based on the stimulated echo acquisition mode (STEAM), with short and long echo time (TE) and allows quantitative measurements of NAAG in the parietal and pregenual anterior cingulate cortex (pgACC) of human brain. Two base- sets for the LCModel have been established using nuclear magnetic resonance simulator software (NMR-SIM). Six healthy volunteers (age 25-35 years) have been examined at 7 T. It has been established that NAAG can be separated and quantifi ed in the parietal location and does not get quantifi ed in the pgACC location when using a short echo time, TE = 20 ms. On the other hand, by using a long echo time, TE = 74 ms, NAAG can be quantifi ed in pgACC structures. LCModel. Introduction. N-Acetylaspartylglutamic acid (NAAG) is a neuropeptide that is the third most prevalent neurotransmitter in the human brain (1). NAAG is produced by the coupling between a glutamic acid (Glu) and the N-acetylaspartic acid (NAA) via a peptide bond. Therefore, it may be diffi cult to distinguish between them on account of the similarity of the chemical structure. In human studies, it has been suggested that NAAG levels are abnormal in patients with schizophrenia (2) and decreased in amyotrophic lateral sclerosis (ALS) (3). In a previous study (4), it had been diffi cult to distinguish NAAG from NAA and Glu using proton magnetic resonance spectroscopy (MRS) at 3 T. As the dominant signal of the NAAG spectrum from the N-acetyl proton resonance peak is located at 2.05 ppm, which is 0.03 ppm away from the corresponding NAA signal at 2.02 ppm (5), a high resolution of metabolite peaks can be obtained using ultrahigh-fi eld strengths such as 7 T (6, 7) or at high fi elds (2 or 3 T), with unusual shimming (8). Proton magnetic resonance spectroscopy provides markers for various human brain diseases (9, 10). Some of the important measurement characteristics of the MRS technique are the signal-to-noise ratio (SNR), spatial and spectral resolution, as well as scan time; thus, several localization methods have been proposed. Single volume spectroscopy (SVS) localization techniques, with pulse sequences based on spin echoes (PRESS) (11) or stimulated echoes (STEAM) (12), provide the highest spectral quality (13), as the lower magnetic fi eld strengths result in a peak overlap of the human brain metabolites, such as, NAA with NAAG. Besides, standard spectroscopic sequences such as STEAM or PRESS will suffer if limited transmitter voltage takes place. This results in a reduced excitation flip angle and consequently insuffi cient excitation in the volume of interest (VOI). Moreover, previous studies have shown that the increase in magnetic field strength increases the 1 H NMR spectral peak separation and SNR and thus provides higher sensitivity when compared with lower field strengths (14, 15). With standard radio-frequency (RF) amplifiers and volume RF coils at 7 T, short 180° refocusing pulses are diffi cult to achieve in most parts of the brain. Therefore, earlier, high field MRS studies frequently employed surface coils with locally higher RF fi eld amplitude (16, 17). However, not all brain areas can be adequately examined using surface coils. As the goal of this study is to quantify the NAAG concentrations in different brain structures, STEAM with short echo time benefits, from reduced signal decay, because of the J-evolution of the coupled spin system, allows a more precise quantification of the metabolites, especially with a short T2 relaxation time (18). Thus, short echo times have been used in several studies (19). In the current study, echo time (TE) was selected to be short and long 20 and 74 ms, respectively. Although earlier studies had employed STEAM with ultrashort echo times (6 ms), they were limited by the surface coils that prevented detection in the deep brain regions (20). Also, a quadrature (transmit/receive) surface RF coil or a half-volume RF coil have been used for the

Aesthetic Contouring of Calf Hypertrophy with Radiofrequency Volume Reduction

Introduction: Asians tend to have short and thick calves. Therefore, a chubby and muscular shape of the legs is of particular concern. Many methods have been performed frequently for calf contouring. In this study, we describe our experience in percutaneous induction of coagulation necrosis with radiofrequency (RF) energy for the reduction of the volume of gastrocnemius muscles (GCMs). Materials and Methods: A total of 360 patients were enrolled in this study from 2009 to 2013. The operations were performed with the patients in a prone position under both local and intravenous anesthesia. The RF energy was delivered along each treatment line, and the total amount of energy applied to each calf was approximately 9.5 kJ to 13.3 kJ. Results: The average reduction in calf circumference was 1.7 cm (5%), and the average change of GCM thickness was 4.11 mm (20%). The difference between the reduction rates was significant (P = .002), which means the rate of reduction in GCM thickness is significantly higher than that of calf circumference reduction. Conclusions: Calf reduction using RF could be used to treat hypertrophic calf muscles with minor improvement and relatively low risk. However, the reduction rate of calf circumference was significantly lower than that of the GCM thickness. This could be explained by the fact that the improvement could be masked by leg edema associated with daily physical activities and substantial compensatory hypertrophy of the soleus muscle. This fact should be clearly communicated to the patients before RF reduction of the calf.

Learning Curve of Septoplasty with Radiofrequency Volume Reduction of the Inferior Turbinate

ObjectivesSince few studies on surgical training and learning curves have been performed, majority of inexperienced surgeons are anxious about performing operations. We aimed to access the results and learning curve of septoplasty with radiofrequency volume reduction (RFVR) of the inferior turbinate.MethodsWe included 270 patients who underwent septoplasty with RFVR of the inferior turbinate by 6 inexperienced surgeons between January 2009 and July 2011. We analyzed success score, cases of revision, cases of complication, operation time, and acoustic rhinometry.ResultsSuccess score was relatively high and every surgeon had few cases of revision and complication. No significant difference was found in success score, revision, complication case, or acoustic rhinometry values between early cases and later cases. Operation time decreased according to increase in experience. However, there was no significant difference in the operation time after more than 30 cases.ConclusionWe can conclude that 30 cases are needed to develop mature surgical skills for septoplasty with RFVR of the inferior turbinate and that training surgeons do not need to be anxious about performing this operation in the unskilled state.

A Gated-7T MRI Technique for Tracking Lung Tumor Development and Progression in Mice after Exposure to Low Doses of Ionizing Radiation

A gated-7T magnetic resonance imaging (MRI) application is described that can accurately and efficiently measure the size of in vivo mouse lung tumors from ∼0.1 mm(3) to >4 mm(3). This MRI approach fills a void in radiation research because the technique can be used to noninvasively measure the growth rate of lung tumors in large numbers of mice that have been irradiated with low doses (<50 mGy) without the additional radiation exposure associated with planar X ray, CT or PET imaging. High quality, high resolution, reproducible images of the mouse thorax were obtained in ∼20 min using: (1) a Bruker 7T micro-MRI scanner equipped with a 60 mm inner diameter gradient insert capable of generating a maximum gradient of 1000 mT/m; (2) a 35 mm inner diameter quadrature radiofrequency volume coil; and (3) an electrocardiogram and respiratory gated Fast Low Angle Shot (FLASH) pulse sequence. The images had an in-plane image resolution of 98 μm and a 0.5 mm slice thickness. Tumor diameter measured by MRI was highly correlated (R(2) = 0.97) with the tumor diameter measured by electronic calipers. Data generated with an initiation/promotion mouse model of lung carcinogenesis and this MRI technique demonstrated that mice exposed to 4 weekly fractions of 10, 30 or 50 mGy of CT radiation had the same lung tumor growth rate as that measured in sham-irradiated mice. In summary, this high-field, double-gated MRI approach is an efficient way of quantitatively tracking lung tumor development and progression after exposure to low doses of ionizing radiation.

Radiofrequency Volume Reduction of Tongue Base: A 12‐Year Experience

Objective: 1) To report on the evolution and success rate of radiofrequency volume reduction of the tongue base over a 12-year period. 2) Introduce a novel method for deploying the RFVR probes to the tongue base without pulling the tongue forward. 3) Show reduced complication rates by avoiding nerves and vessels. 4) Show increased success rate with increased number of lesions per treatment session. 5) Demonstrate the possibility of treating the genioglossus and geniohyoid muscles to shorten these muscles and retract the tongue anteriorly. Method: In an IRB-approved prospective study at a community hospital, over 400 patients with obstructive sleep apnea over a 12 year period were selected for RFVR of the tongue base when there is evidence of hypopharyngeal involvement. Treatment evolved from single pronged to a double pronged probe with the rapid lesion mode and from to 2 lesions to 14 lesions. RFVR is usually performed in conjunction as part of multilevel treatment. Polysomnography prior to and 3 months after treatment were analyzed. Complications were recorded. Success is defined as RDI less than 20 and a greater than 50% reduction from preoperative levels. Results: Success rates increased from 58% to 68% while the number of sessions of treatment decreased from 4 to 1 as the number of lesions increased from 2 to 14. There were no major complications. Conclusion: RFVR of tongue base has evolved over a 12-year period to become a more efficacious and integral part of multilevel treatment for OSA.

Radiofrequency Volume Turbinate Reduction versus Partial Turbinectomy: Clinical and Histological Features

Nasal obstruction is a common symptom related to turbinate hypertrophy in 20% of cases. When medical treatment failed different surgical options were available. Actually, nasal physiology impairment after surgical treatment is not fully clear. This study evaluates microscopic mucosal changes and physiological function, by means of mucociliary transport time (MCT), after radiofrequency volume turbinate reduction and partial inferior turbinectomy. Forty-eight nonallergic patients were treated for chronic nasal obstruction. Twenty-six patients (group A) underwent radiofrequency turbinate reduction and 22 patients (group B) underwent partial turbinectomy associated with septoplasty. Mucosal specimens obtained before T(0) and 6 months (T(1)) after surgery were compared by means of optical microscope and transmission electron microscope. All patients were evaluated using MCT at T(0) and T(1). Optical analysis showed circumscribed squamous metaplasia and fibrosis in specimens obtained from group A. Same changes were more evident in group B. Ultrastructural analysis evidenced loss of ciliated epithelium in group B, whereas in group A a normal number of cilia was found. In all patients at T(1), MCT time was prolonged in comparison with the preoperative values. After surgery, group B showed significantly prolonged MCT in comparison with group A (p < 0.05). In our study both surgical techniques achieved good clinical outcomes with improved nasal function, although the ciliated epithelium appeared partially impaired. These findings resulted in a prolonged MCT in all patients, especially in those treated with partial turbinectomy. Compared to partial resection, intraturbinal turbinate reduction seems to be the method of choice to better preserve nasal physiology.

Resonant Mode Reduction in Radiofrequency Volume Coils for Ultrahigh Field Magnetic Resonance Imaging

In a multimodal volume coil, only one mode can generate homogeneous Radiofrequency (RF) field for Magnetic Resonance Imaging. The existence of other modes may increase the volume coil design difficulties and potentially decreases coil performance. In this study, we introduce common-mode resonator technique to high and ultrahigh field volume coil designs to reduce the resonant mode while maintain the homogeneity of the RF field. To investigate the design method, the common-mode resonator was realized by using a microstrip line which was split along the central to become a pair of parallel transmission lines within which common-mode currents exist. Eight common-mode resonators were placed equidistantly along the circumference of a low loss dielectric cylinder to form a volume coil. Theoretical analysis and comparison between the 16-strut common-mode volume coil and a conventional 16-strut volume coil in terms of RF field homogeneity and efficiency was performed using Finite-Difference Time-Domain (FDTD) method at 298.2 MHz. MR imaging experiments were performed by using a prototype of the common-mode volume coil on a whole body 7 Tesla scanner. FDTD simulation results showed the reduced number of resonant modes of the common-mode volume coil over the conventional volume coil, while the RF field homogeneity of the two type volume coils was kept at the same level. MR imaging of a water phantom and a kiwi fruit showing the feasibility of the proposed method for simplifying the volume coil design is also presented.

Excessive Gastrocnemius Fibrosis Developed After Radiofrequency-Induced Cosmetic Volume Reduction

Cosmetic shaping of the lower leg is becoming increasingly popular. The use of radiofrequency therapy in cosmetic medicine also is growing. To date, no serious complications have been reported after the use of cosmetic radiofrequency therapy. This report describes a patient who presented at the author's clinic with a disabling ankle plantarflexion contracture in both calves that developed during a period of 18months after cosmetic radiofrequency volume reduction. This reduction, performed at another clinic, involved applying a bipolar electrode with a mean power of 35W at each of approximately 100 spots for 2 to 4s. On each calf, 15kJ was applied in a crisscross fashion. Magnetic resonance imaging and muscle biopsy indicated excessive gastrocnemius fibrosis. The patient was treated using botulinum toxin injections followed by serial castings and intensive physiotherapy. After treatment, the patient was able to walk with less difficulty and showed no tiptoeing. This appears to be the first report of serious muscle contracture after cosmetic radiofrequency volume reduction requiring extensive rehabilitation management.

Cryothermie: Eine neue Perspektive in der interventionellen Therapie von Herzrhythmusstörungen?

Cryothermal ablation is a new method in cardiac electrophysiology for the percutaneous catheter ablation of cardiac arrhythmias. Cryothermal mapping make possible the functional assessment of a particular site before permanent ablation. In this way the targeted tissue may be confirmed as safe for ablation. This is useful in high-risk ablation, for example next to the AV node. In this method pressurized liquid nitrogen is delivered to the tip of the ablation catheter. Cooling of the tip is temperature-controlled. Cryothermal balloons are also available, in addition to standard cryothermal catheters, for the isolation of pulmonary veins. The tissue freezing provides high catheter stability. Cryothermal lesions have a similar depth to radiofrequency energy, but area and volume of the lesions are reduced. Furthermore, they are well demarkated and the incidence of thrombus-formation is reduced. Cryothermal ablation has been evaluated for the treatment of AV-nodal reentry tachycardia (AVNRT), accessory pathways, atrial flutter, atrial fibrillation and ventricular tachycardias originating in the right ventricular outflow tract. Current experience indicates that the method is painless for the patient and safe. However, its use seems to be limited by a longer ablation time and lower efficacy. Further studies evaluating long-term success of cryothermal ablation are warranted. For high-risk ablations cryothermal energy is helpful and should be used for para-Hisian accessory pathways and difficult cases of AVNRT. It has a widely demonstrated safety profile. The clinical efficacy will have to be evaluated in further studies.

Tongue base suspension and radiofrequency volume reduction: a comparison between 2 techniques for the treatment of sleep-disordered breathing

Purpose Lingual suspension (LS) and tongue base radio frequency volume reduction (RFVR) have been proposed as means of correcting the obstruction caused by the collapse or hypertrophy of the tongue base in patients having sleep-disordered breathing (SDB). The aim of this study was to evaluate and compare long-term results (6 months and 2 years) in a population of 24 patients having mild obstructive sleep apnea syndrome (OSAS), of whom 12 were treated with LS and 12 with RFVR. Materials and methods The study included 24 patients having mild OSAS (apnea-hypopnea index between 10 and 20). All patients were assessed by means of the Epworth Sleepiness Scale, collection of anthropomorphic data, fiber-optic evaluation with Muller's maneuver, cephalometric assessment, and polysomnography. Lingual suspension was performed under general anesthesia with cervical cutaneous access. Radio frequency volume reduction was performed under local anesthesia with an Ellman Surgitron Dual RF unit (Ellman International, Inc., New York, NY), using a resterilizable bipolar terminal prototype. The same ear, nose, and throat examinations and polysomnography were carried out 6 months and 2 years after the surgical procedure. Results The results were evaluated according to the criteria by Sher ( Sleep. 1996,19:156–177); after 6 months, the success percentage was 67% in patients treated with LS and 75% in those with RFVR. These percentages dropped to 42% in the first group and 33% in the second group after 24 months. Conclusions Lingual suspension and RFVR are simple procedures that can be quickly performed and are well tolerated by patients. However, their effectiveness drops after 2 years. Our experience has therefore led us to conclude that the minimally invasive treatment for tongue base surgery can guarantee long-term results only in 42% and 33% of patients, respectively. Moreover, RFVR is preferable because it is simpler to perform and less invasive than LS, and it can be repeated over time.

3D estimation of soft biological tissue deformation from radio-frequency ultrasound volume acquisitions

The current research and development of 2D (matrix-shaped) transducer arrays to acquire 3D ultrasound data sets provides new insights into medical ultrasound applications and in particular into elastography. Until very recently, tissue strain estimation techniques commonly used in elastography were mainly 1D or 2D methods. In this paper, a 3D technique estimating biological soft tissue deformation under load from ultrasound radiofrequency volume acquisitions is introduced. This method locally computes axial strains, while considering lateral and elevational motions. Optimal deformation parameters are estimated as those maximizing a similarity criterion, defined as the normalized correlation coefficient, between an initial region and its deformed version, when the latter is compensated for according to these parameters. The performance of our algorithm was assessed with numerical data reproducing the configuration of breast cancer, as well as a physical phantom mimicking a pressure ulcer. Simulation results show that the estimated strain fields are very close to the theoretical values, perfectly discriminating between the harder lesion and the surrounding medium. Experimental strain images of the physical phantom demonstrated the different structures of the medium, even though they are not all detectable on the ultrasound scans. Finally, both simulated and experimental results demonstrate the ability of our algorithm to provide good-quality elastograms, even in the conditions of significant out-of-plane motion.

High‐field head radiofrequency volume coils using transverse electromagnetic (TEM) and phased array technologies

This article describes technological advances in quadrature transverse electromagnetic (TEM) volume coils and phased arrays reported recently from our laboratory developed for MRI and MRS imaging of the human brain. The first part of this work presents a new method for tuning TEM volume coils based on measurements of the radiofrequency current distribution in the coil elements. This technique facilitates bench adjustment of the coils' homogeneity and is particularly important for tuning double-tuned TEM volume coils. We have also used this method to optimize other TEM configurations such as a quadrature TEM half-volume coil and a split TEM coil. TEM half-volume coils provide greater sensitivity over localized regions than conventional full-volume coils, and the split TEM coil provides greater patient access and ease of use. The second part of this work describes the development of single-tuned and double-tuned transmit TEM volume coils in combination with phased arrays. A variety of different techniques for active detuning of single-tuned and double-tuned TEM volume coils are presented along with the development of phased arrays and transmission line preamplifier decoupling. The final section describes the use of counter rotating current (CRC) surface coils in phased arrays. Because of the intrinsic isolation of CRC coils from transmit volume coils, CRC arrays can be used simultaneously with volume coils for both reception and transmission. Near the center of the human head where both the phased array and the volume coil produce similar sensitivities, simultaneous reception enhances the signal-to-noise ratio. Conversely, simultaneous transmission can be used to boost the transmit field in peripheral brain regions from the volume coil to provide a more homogeneous transmit field.

Minimally Invasive Single‐Stage Multilevel Treatment for Obstructive Sleep Apnea/Hypopnea Syndrome

To assess subjective and objective improvement after single-stage multilevel minimally invasive treatment for obstructive sleep apnea/hypopnea syndrome (OSAHS). A retrospective review of a prospective dataset of patients treated in a tertiary care referral center. Charts of 145 patients with mild/moderate OSAHS treated with a single-stage multilevel minimally invasive technique were reviewed to abstract pre- and posttreatment symptoms and polysomnographic data. One hundred twenty-two patients had minimum follow-up of 6 (range, 6-23) months and complete data available for analysis. All patients studied had three-level treatment that included nasal surgery, palatal stiffening by Pillar implant technique, and radiofrequency volume reduction of the tongue base. Primary outcomes included change from baseline in apnea/hypopnea index (AHI). Secondary outcomes included change in Epworth Sleepiness Scale (ESS) and bed-partner assessed snoring visual analogue scale (VAS, 0-10), pain levels, narcotic use, and complications. Mean AHI decreased from 23.2 +/- 7.6 preoperatively to 14.5 +/- 10.2 postoperatively (P < .0001). Classical "cure" was achieved in 54 (47.5%) patients. Mean ESS decreased from 9.7 +/- 3.9 preoperatively to 6.9 +/- 3.3 postoperatively (P < .0001). Mean snoring VAS decreased from 9.4 +/- 0.9 preoperatively to 3.2 +/- 2.4 postoperatively (P <. 0001). Polysomnographic respiratory parameters, ESS, and snoring VAS significantly improved in patients with mild/moderate OSAHS treated with single-stage multilevel minimally invasive surgery. Multilevel minimally invasive single-stage surgery is a valid option for selected patients with mild/moderate OSAHS with the understanding that they may require secondary treatment.

Radiofrequency Volume Reduction of Gastrocnemius Muscle Hypertrophy for Cosmetic Purposes

Muscularly prominent calves, caused mainly by hypertrophy of the gastrocnemius muscle (GCM), are prevalent among Asian women, and this condition can be a significant factor leading to psychological stress. The authors have devised a method for contouring the calf using radiofrequency (RF) applications to the GCMs to correct thick, muscular legs. This study was performed to investigate the effects of RF energy in reducing enlarged GCMs for 250 patients (249 women and 1 man) who sought aesthetic consultation for problems such as thick, muscular, asymmetric, or bowed calves. The operations were performed from June 2004 to April 2006. The patients first received a local anesthetic and sedation. After application of RF current, the prominent muscular contours improved, and the GCMs were contoured to an appropriate proportional volume. The range of the reductions in the calf circumferences at their thickest levels was 1 to 6 cm (mean, 2.5 cm) during the follow-up visits 6 months after the procedures. Most of the patients could return to their activities of daily living, except for exercise, after 1 to 7 days, and they were satisfied with the improved aesthetic contour lines of their lower legs. Clinical photography and ultrasonic examination were performed, and the leg circumferences were measured. Radiofrequency-induced coagulation tissue necrosis of the muscles caused no functional disabilities, and the clinical improvement was well maintained after the treatments for up to 17 months of follow-up evaluation.

Treatment of hypertrophic palatine tonsils using bipolar radiofrequency-induced thermotherapy (RFITT)

Conclusion. Radiofrequency volume reduction of palatine tonsils is a gentle and safe treatment method in selected patients, which should carefully be considered as an alternative to tonsillectomy or tonsillotomy. Objectives. The aim of this study was the evaluation of bipolar radiofrequency-induced thermotherapy (RFITT) compared to standard blunt dissection tonsillectomy (TE) for the volume reduction of palatine tonsils in chronic tonsillar hypertrophy. Patients and methods. A total of 137 patients (98 children) were treated in two groups in a prospective controlled, randomized clinical trial. The TE group underwent standard tonsillectomy using blunt dissection. The RFITT group underwent interstitial RF ablation. Perioperative blood loss and duration of surgery were monitored. Tonsil volume reduction in the RFITT group was measured by sonography. Postoperative pain, as well as difficulty in swallowing and speaking, were evaluated using visual analog scales. Results. In the RFITT group, we found an average tonsil volume reduction of 40%, at about 3 weeks after treatment. Postoperative pain, swallowing and speaking difficulties, and perioperative blood loss were significantly lower, and the duration of surgery was significantly shorter (all p<0.05) in the RFITT group. Preservation of the treatment results was monitored until 6 months after treatment, with no after effects during this time period.

A theoretical comparison of two optimization methods for radiofrequency drive schemes in high frequency MRI resonators

In this paper, numerical simulations are used in an attempt to find optimal source profiles for high frequency radiofrequency (RF) volume coils. Biologically loaded, shielded/unshielded circular and elliptical birdcage coils operating at 170 MHz, 300 MHz and 470 MHz are modelled using the FDTD method for both 2D and 3D cases. Taking advantage of the fact that some aspects of the electromagnetic system are linear, two approaches have been proposed for the determination of the drives for individual elements in the RF resonator. The first method is an iterative optimization technique with a kernel for the evaluation of RF fields inside an imaging plane of a human head model using pre-characterized sensitivity profiles of the individual rungs of a resonator; the second method is a regularization-based technique. In the second approach, a sensitivity matrix is explicitly constructed and a regularization procedure is employed to solve the ill-posed problem. Test simulations show that both methods can improve the B1-field homogeneity in both focused and non-focused scenarios. While the regularization-based method is more efficient, the first optimization method is more flexible as it can take into account other issues such as controlling SAR or reshaping the resonator structures. It is hoped that these schemes and their extensions will be useful for the determination of multi-element RF drives in a variety of applications.

Radiofrequency Volume Tissue Reduction of the Tonsils: Case Report and Histopathologic Findings

Innovative new techniques to resect tonsillar tissue have been described in the recent literature. We report the case of a patient who underwent volume reduction of tonsillar tissue by radiofrequency energy under local anesthesia in an office setting. Treatment resulted in a reduction of tonsillar size with minimal pain, which can be attributed to the avoidance of mucosal interruption. The patient subsequently underwent standard tonsillectomy, which allowed us to examine the histopathology of the tissue that was treated with radiofrequency. In doing so, we noted an absence of fibrosis and preservation of normal histologic architecture. We conclude that performing volume reduction of tonsillar tissue by applying radiofrequency energy to the stroma of the tonsils without temperature control results in objective improvement in airway size with minimal effects on the histopathology of the tonsillar stroma. Mucosa-sparing tonsillar reduction may be a preferable alternative to other techniques of tonsillar reduction, especially for young children, who would experience a nearly pain-free procedure.