Quality assurance guidelines for interstitial hyperthermia.

Quality assurance (QA) guidelines are essential to provide uniform execution of clinical hyperthermia treatments and trials. This document outlines the clinical and technical consequences of the specific properties of interstitial heat delivery and specifies recommendations for hyperthermia administration with interstitial techniques. Interstitial hyperthermia aims at tumor temperatures in the 40-44 °C range as an adjunct to radiation or chemotherapy. The clinical part of this document imparts specific clinical experience of interstitial heat delivery to various tumor sites as well as recommended interstitial hyperthermia workflow and procedures. The second part describes technical requirements for quality assurance of current interstitial heating equipment including electromagnetic (radiative and capacitive) and ultrasound heating techniques. Detailed instructions are provided on characterization and documentation of the performance of interstitial hyperthermia applicators to achieve reproducible hyperthermia treatments of uniform high quality. Output power and consequent temperature rise are the key parameters for characterization of applicator performance in these QA guidelines. These characteristics determine the specific maximum tumor size and depth that can be heated adequately. The guidelines were developed by the ESHO Technical Committee with participation of senior STM members and members of the Atzelsberg Circle.

Multi-site voxel-based morphometry--not quite there yet.

Voxel-based morphometry (VBM) is a widely applied method in computational neurosciences but it is currently recommended to compare only data collected at a single MRI scanner. Multi-site VBM would be a desirable approach to increase group size and, thus, statistical power. We aimed to assess if multi-site VBM is feasible on similar hardware and compare the magnitude of inter- and intra-scanner differences. 18 healthy subjects were scanned in two identical 3T MRI scanners using different head coil designs, twice in scanner A and once in scanner B. 3D T1-weighted images were processed with SPM8 and FSL4.1 and compared as paired t-test (scan versus re-scan) on a voxel basis by means of a general linear model (GLM). Additionally, coefficient-of-difference (coeffD) maps were calculated for respective pairs of gray matter segmentations. We found considerable inter-scanner differences clearly exceeding a commonly used GLM significance threshold of p<0.05 (FWE corrected). The spatial pattern of detected differences was dependent on whether SPM8 or FSL4.1 was used. The inclusion of global correcting factors either aggravated (SPM8) or reduced the GLM detected differences (FSL4.1). The coeffD analysis revealed markedly higher variability within the FSL4.1 stream both for the inter- and the intra-scanner comparison. A lowered bias cutoff (30 mm FWHM) in SPM8 improved the comparability for cortical areas. Intra-scanner scan/re-scan differences were generally weaker and did not exceed a p<0.05 (FWE corrected) threshold in the GLM analysis. At 3T profound inter-scanner differences are to be expected that could severely confound an unbalanced VBM analysis. These are like related to the receive bias of the radio-frequency hardware.

Evaluation of two new recombinant guinea-pig lipocalins, Cav p 2 and Cav p 3, in the diagnosis of guinea-pig allergy.

BACKGROUND: Guinea-pigs, classical laboratory animals now often kept as pets, regularly elicit important allergic reactions. Two guinea-pig allergens have been described previously to some extent; however, biomolecular and immunological data are lacking. OBJECTIVE: To identify major guinea-pig allergens, produce them as recombinant proteins and define their allergenic potential and clinical importance in allergic patients. METHODS: Protein extracts were prepared from various guinea-pig tissues and allergens were purified by ion exchange chromatography. The N-termini of two immunoglobulin E (IgE)-reactive proteins were determined and degenerate primers were designed for cDNA amplification by RT-PCR. Allergenic properties of recombinant proteins were assayed by immunoblotting, ELISA and mediator release assays. Specific IgE were quantified in the sera of 26 guinea-pig-allergic patients. RESULTS: Major IgE-reactive proteins were detected in submaxillary and harderian gland extracts. Two proteins were identified and the cDNAs were cloned. The 17 kDa protein expressed in the harderian gland corresponds to the previously described Cav p 2. The 19 kDa protein, Cav p 3, is a new allergen expressed in the submaxillary gland. Recombinant Cav p 2 and Cav p 3 were recognized by IgE antibodies from 65% and 54% of guinea-pig-allergic patients, respectively. Both proteins demonstrated equivalent allergenic activity in the mediator release assays. CONCLUSION AND CLINICAL RELEVANCE: Two major guinea-pig allergens, Cav p 2 and Cav p 3, have been characterized and produced as recombinant proteins. Combined to guinea-pig serum albumin, the new allergens proved to be valuable in the component-resolved diagnosis of guinea-pig allergy.

Cortisol and behavioral responses of working dogs to environmental challenges.

This paper's primary objective is to analyse the physiological (cortisol) and behavioral responses of military working dogs (MWD). Dogs (N=27) were submitted twice to environmental challenges (challenge 1 and 2, 20 days in-between) composed of social (training), visual (mobile toy car) and auditory (air blast) stimuli. Cortisol levels decreased back to the baseline after the second challenge. The behavioral observations showed that these MWD were more active, and presented less stereotypic behaviors (pacing, manipulation of the environment) during both visual challenges, whereas half low posture was observed during the first but not during the second visual challenge. The present study shows that this group of MWD still has an adaptation capacity to an environmental challenge (return to baseline of the cortisol levels, a higher posture during the second than at the first challenge). These results are encouraging and indicate that the dogs might have a diminished welfare (i.e. stereotypic behaviors), but are not chronically stressed.

Scheduling Anesthesia Time Reduces Case Cancellations and Improves Operating Room Workflow in a University Hospital Setting.

BACKGROUND: A new method of scheduling anesthesia-controlled time (ACT) was implemented on July 1, 2012 in an academic inpatient operating room (OR) department. This study examined the relationship between this new scheduling method and OR performance. The new method comprised the development of predetermined time frames per anesthetic technique based on historical data of the actual time needed for anesthesia induction and emergence. Seven "anesthesia scheduling packages" (0 to 6) were established. Several options based on the quantity of anesthesia monitoring and the complexity of the patient were differentiated in time within each package. STUDY DESIGN: This was a quasi-experimental time-series design. Relevant data were divided into 4 equal periods of time. These time periods were compared with ANOVA with contrast analysis: an intervention, pre-intervention, and post-intervention contrast were tested. All emergency cases were excluded. A total of 34,976 inpatient elective cases performed from January 1, 2010 to December 31, 2014 were included for statistical analyses. RESULTS: The intervention contrast showed a significant decrease (p < 0.001) of 4.5% in the prediction error. The total number of cancellations decreased to 19.9%. The ANOVA with contrast analyses showed no significant differences with respect to under- and over-used OR time and raw use. Unanticipated results derived from this study, allowing for a smoother workflow: eg anesthesia nurses know exactly which medical equipment and devices need to be assembled and tested beforehand, based on the scheduled anesthesia package. CONCLUSIONS: Scheduling the 2 major components of a procedure (anesthesia- and surgeon-controlled time) more accurately leads to fewer case cancellations, lower prediction errors, and smoother OR workflow in a university hospital setting.

Survival benefit of hyperthermia in a prospective randomized trial of brachytherapy boost +/- hyperthermia for glioblastoma multiforme.

PURPOSE: To determine if adjuvant interstitial hyperthermia (HT) significantly improves survival of patients with glioblastoma undergoing brachytherapy boost after conventional radiotherapy. METHODS AND MATERIALS: Adults with newly-diagnosed, focal, supratentorial glioblastoma < or = 5 cm in diameter were registered postoperatively on a Phase II/III randomized trial and treated with partial brain radiotherapy to 59.4 Gy with oral hydroxyurea. Those patients whose tumor was still implantable after teletherapy were randomized to brachytherapy boost (60 Gy at 0.40-0.60 Gy/h) +/- HT for 30 min immediately before and after brachytherapy. Time to progression (TTP) and survival from date of diagnosis were estimated using the Kaplan-Meier method. RESULTS: From 1990 to 1995, 112 eligible patients were entered in the trial. Patient ages ranged from 21-78 years (median, 54 years) and KPS ranged from 70-100 (median, 90). Most commonly due to tumor progression or patient refusal, 33 patients were never randomized. Of the patients, 39 were randomized to brachytherapy ("no heat") and 40 to brachytherapy + HT ("heat"). By intent to treat, TTP and survival were significantly longer for "heat" than "no heat" (p = 0.04 and p = 0.04). For the 33 "no heat" patients and 35 "heat" patients who underwent brachytherapy boost, TTP and survival were significantly longer for "heat" than "no heat" (p = 0.045 and p = 0.02, respectively; median survival 85 weeks vs. 76 weeks; 2-year survival 31% vs. 15%). A multivariate analysis for these 68 patients adjusting for age and KPS showed that improved survival was significantly associated with randomization to "heat" (p = 0.008; hazard ratio 0.51). There were no Grade 5 toxicities, 2 Grade 4 toxicities (1 on each arm), and 7 Grade 3 toxicities (1 on "no heat" and 6 on the "heat" arm). CONCLUSION: Adjuvant interstitial brain HT, given before and after brachytherapy boost, after conventional radiotherapy significantly improves survival of patients with focal glioblastoma, with acceptable toxicity.

The development of intracavitary ultrasonic applicators for hyperthermia: a design and experimental study.

This study investigated the design concepts and development of a multielement intracavitary ultrasound applicator for use in hyperthermia. A necessary condition imposed on these applicators is that each transducer element be separately powered and produce collimated beams. This way, the power deposition within the target volume can be controlled by varying the power to each element. Theoretical computer simulations (acoustic and thermal) and bench experiments were used to determine the constraints on the transducer element size and the spacing between them. These have shown that the length of the cylindrical segments (or subsections of) must be greater than approximately 10 lambda for proper collimation and that the spacing between them must be less than approximately 1.5 mm for uniform heating. With these design principles in mind, applicators were constructed using sections of cylindrical transducers (wall-thickness resonance). These were surrounded by temperature-controlled circulating water which was enclosed by a latex membrane. This allowed for acoustic coupling and additional control over the depth of the maximum temperature from the cavity wall. This depth could be varied between the cavity surface and up to 1.5 cm for circulating water temperatures between 5 and 42 degrees C, respectively. These applicators were tested in vivo and were able to induce controlled transrectal heating, at depths of 2-3 cm, in the canine rectum and prostate gland.

Thermal and SAR characterization of multielement dual concentric conductor microwave applicators for hyperthermia, a theoretical investigation.

Six aperture array dual concentric conductor (DCO) microwave hyperthermia applicators were studied using theoretical models to characterize power deposition (SAR) and steady state temperature distributions in perfused tissue. SAR patterns were calculated using the finite difference time domain (FDTD) numerical method, and were used as input to a finite difference thermal modeling program based on the Pennes Bio-Heat Equation in order to calculate corresponding temperature distributions. Numerous array configurations were investigated including the use of different size DCC apertures (2, 3, and 4 cm), different spacing between apertures (1.0-2.0 cm), and different water bolus thicknesses (5-15 mm). Thermal simulations were repeated using blood perfusion values ranging from 0.5 to 5 kg/m3 s. Results demonstrate the ability of DCC array applicators to effectively and uniformly heat tissue down to a depth of 7.5-10 mm below the skin surface for a large number of different combinations of DCC element size, spacing, and water bolus thickness. Results also reveal the close correlation between SAR patterns and corresponding temperature distributions, verifying that design studies of the applicator can be performed confidently by analysis of SAR, from which the thermal behavior can be estimated. These simulations are useful in the design optimization of large microwave DCC array applicators for superficial tissue heating and for identifying appropriate aperture spacing and bolus thickness parameters for different size DCC aperture arrays and tissue blood perfusion conditions.

An improved bolus configuration for commercial multielement ultrasound and microwave hyperthermia systems.

A simple modification is presented for two commercially available hyperthermia applicators which dramatically improves the regulation and dynamic control of the temperature at the bolus/tissue interface. This alteration requires the addition of a variable speed pump, bubble trap, simple heat exchanger, and a few minor changes to the existing system. With this modified design, the water within the bolus is directly circulated and temperature controlled. The convective nature of the circulating system ensures uniform temperature throughout the extended bolus and increases the thermal energy transfer at the bolus/tissue interface. This modification also provides significantly improved flexibility in controlling the treatment temperature distributions since the bolus/tissue interface temperature can now be dynamically varied during a treatment, in addition to adjusting the applicator power output and frequency.

Evaluation of multielement catheter-cooled interstitial ultrasound applicators for high-temperature thermal therapy.

Catheter-cooled (CC) interstitial ultrasound applicators were evaluated for their use in high-temperature coagulative thermal therapy of tissue. Studies in ex vivo beef muscle were conducted to determine the influences of applied electrical power levels (5-20 W per element), catheter flow rate (20-60 ml min(-1)), circulating water temperature (7-40 degrees C), and frequency (7-9 MHz) on temperature distribution and thermal lesion geometry. The feasibility of using multiple interstitial applicators to thermally coagulate a predetermined volume of tissue was also investigated. Results of these studies revealed that the directional shape of the thermal lesions is maintained with increasing time and power. Radial depths of the thermal lesions ranged from 10.7 +/- 0.7 mm after heating for 4 min with an applied power level of 5 W, to 16.2 +/- 1.4 mm with 20 W. The axial length of the thermal lesions is controlled tightly by the number of active transducers. A catheter flow rate of 20 to 40 ml min(-1) (52.2 +/- 5.5 kPa at 40 ml min(-1)) with 22 degrees C water was determined to provide sufficient cooling of the transducers for power levels used in this study. In vivo temperatures measured in the center of a 3-cm-diam peripheral implant of four applicators in pig thigh muscle reached 89.3 degrees C after 4 min of heating, with boundaries of coagulation clearly defined by applicator position and directivity. Conformability of heating in a clinically relevant model was demonstrated by inserting two directional CC applicators with a 2 cm separation within an in vivo canine prostate, and generating a thermal lesion measuring 3.8 cm x 2.2 cm in cross section while directing energy away from, and protecting the rectum. Maximum measured temperatures at midgland exceeded 90 degrees C within 20 min of heating. The results of this study demonstrate the utility of single or multiple CC applicators for conformal thermal coagulation and high temperature thermal therapy, with potential for clinical applications in sites such as prostate, liver, breast, or uterus.

Control of interstitial thermal coagulation: comparative evaluation of microwave and ultrasound applicators.

This study presents a comparative evaluation of the control of heating and thermal coagulation with microwave (MW) and ultrasound (US) interstitial applicators. Helical coil MW antennas (17 mm and 25 mm length radiating antennae) were tested using an external implant catheter (2.2 mm o.d.) with water-cooling. US applicators with tubular transducers (2.2 and 2.5 mm o.d., 10 mm length, single-element and 3-element) were utilized with a direct-coupled configuration and internal water-cooling. Measurements of E-field distributions (for MW) and acoustic beam distributions (for US) were used to characterize the applicator energy output. Thermal performance was evaluated through multiple heating trials in vitro (bovine liver) and in vivo (porcine thigh muscle and liver) at varied levels of applied power (20-40 W for microwave, 15-35 W for ultrasound) and heating times (0.5-5 min). Axial temperature distributions in the tissue were recorded during heating, and dimensions of the resulting lesions of thermal coagulation were measured. Both MW and US applicators produced large volumes of tissue coagulation ranging from 8 to 20 cm3 with singular heating times of 5 min. Radial depth of lesions for both MW and US applicators increased with heating duration and power levels, though US produced notably larger lesion diameters (30-42 mm for US vs 18-26 mm for MW, 5 min heating). Characteristic differences between the applicators were observed in axial energy distribution, tissue temperatures, and thermal lesion shapes. MW lesions increased significantly in axial dimensions (beyond the active applicator length) as applied power level and/or heating duration was increased, and lesion shapes were generally not uniform. US provided greater control and uniformity of heating, with energy deposition and axial extent of thermal lesions corresponding to the length of the active transducer(s). The improved ability to control the extent of thermal coagulation demonstrated by the US applicators provides greater potential to target a specific region of tissue.

Air-cooling of direct-coupled ultrasound applicators for interstitial hyperthermia and thermal coagulation.

The feasibility of using air-cooling to improve the thermal penetration of direct-coupled interstitial ultrasound (US) applicators was investigated using biothermal simulations, bench experiments, phantom testing, and in vivo thermal dosimetry. Two applicator configurations using tubular US transducers were constructed and tested. The first design, intended for simultaneous thermobrachy-therapy, utilizes a 2.5 mm OD transducer with a central lumen to accommodate a radiation source from remote afterloaders. The second applicator consists of a 2.2 mm OD transducer designed for coagulative thermal therapy. Both designs provide cooling of the inner transducer surface by the counterflow of chilled air or CO2 gas through the annulus of the enclosed applicator. The average convective heat transfer (ha) associated with each applicator was determined empirically from curve-fits of radial steady-state temperatures measured in a tissue-mimicking phantom. High levels of convective heat transfer (ha > 500 W m-2 degrees C-1) were demonstrated in both designs at relatively low flow rates (< 5 L min-1). Transient and steady-state radial heating profiles were also measured in vivo (pig thigh muscle) with and without cooling. The therapeutic radius for hyperthermia (41-45 degrees C) was extended from 5-6 mm (without cooling) to 11-19 mm with air-cooling (4.8 L min-1, airflow 10 degrees C), effectively doubling and tripling the thermal penetration in vivo. Similar improvements were demonstrated at higher temperatures with the thermal coagulation applicator. Biothermal simulations, which modeled the physical, thermal, and acoustic parameters of the air-cooled applicator and surrounding tissue, were also used to investigate potential improvements in heating patterns. The simulated radial heating profiles with transducer cooling demonstrated significantly enhanced thermal penetration over the experimental range of convective transfer, and also agreed with in vivo results. These theoretical and experimental results clearly show air-cooling controls the transducer surface temperature, significantly increases thermal penetration, and produces a greater treatment volume for direct-coupled US applicators in hyperthermia and thermal coagulation.

Transurethral ultrasound applicators with directional heating patterns for prostate thermal therapy: in vivo evaluation using magnetic resonance thermometry.

A catheter-based transurethral ultrasound applicator with angularly directional heating patterns has been designed for prostate thermal therapy and evaluated in canine prostate in vivo using MRI to monitor and assess performance. The ultrasound transducer array (3.5 mm diameter tubular transducers, 180 degrees active sectors, approximately 7.5 MHz) was integrated to a flexible delivery catheter (4 mm OD), and encapsulated within an expandable balloon (35 mm x 10 mm OD, 80 ml min(-1) ambient water) for coupling and cooling of the prostatic urethra. These devices were used to thermally coagulate targeted portions of the canine prostate (n = 2) while using MR thermal imaging (MRTI) to monitor the therapy. MRI was also used for target definition, positioning of the applicator, and evaluation of target viability post-therapy. MRTI was based upon the complex phase-difference mapping technique using an interleaved gradient echo-planar imaging sequence with lipid suppression. MRTI derived temperature distributions, thermal dose exposures, T1-contrast enhanced MR images, and histology of sectioned prostates were used to define destroyed tissue zones and characterize the three-dimensional heating patterns. The ultrasound applicators produced approximately 180 degrees directed zones of thermal coagulation within targeted tissue which extended 15-20 mm radially to the outer boundary of the prostate within 15 min. Transducer activation lengths of 17 mm and 24 mm produced contiguous zones of coagulation extending axially approximately 18 mm and approximately 25 mm from base to apex, respectively. Peak temperatures around 90 degrees C were measured, with approximately 50 degrees C-52 degrees C corresponding to outer boundary t43 = 240 min at approximately 15 min treatment time. These devices are MRI compatible, and when coupled with multiplanar MRTI provide a means for selectively controlling the length and sector angle of therapeutic thermal treatment in the prostate.

Angular directivity of thermal coagulation using air-cooled direct-coupled interstitial ultrasound applicators.

The performance characteristics and thermal coagulation of tissue produced by directional air-cooled, direct-coupled interstitial ultrasound (US) applicators were evaluated. Prototype applicators (2.2 mm o.d.) were constructed using cylindrical transducers sectored into angular active zones of 90 degrees, 200 degrees, 270 degrees, and 360 degrees. Acoustic characterization of the applicators showed the beam output to be angularly directed from the active sector of the transducer and collimated within the axial extent. Empirical determination of the average convective heat transfer coefficient, resulting from airflow cooling the inner surface of the transducer, showed significantly high levels of transfer (> 700 W m(-2) degrees C(-1)) with a flow rate of 5.6 L min(-1). Thermal performance of the applicators was characterized through high temperature heating in vivo (porcine thigh muscle, 11 trials) and in vitro (bovine liver, 46 trials). Results demonstrated directional coagulation of tissue, with good correlation between the angular extent of the lesions and the active acoustic sector. Radial depth of coagulation with a 200 degrees applicator extended 8-17 mm, with a heating time of 1-10 min, respectively. Angular and axial lesion shape remained similar over the course of 1-10 min heating trials. Implementation of air-cooling within direct-coupled interstitial US applicators provided enhanced directivity of heating in angular and axial dimensions, and significantly increased the power handling and radial depth of tissue coagulation.

Ultrasound technology for hyperthermia.

Hyperthermia (HT) is used in the clinical management of cancer and benign disease. Numerous biological and clinical investigations have demonstrated that HT in the 41-45 degrees C range can significantly enhance clinical responses to radiation therapy, and has potential for enhancing other therapies, such as chemotherapy, immunotherapy and gene therapy. Furthermore, high-temperature hyperthermia (greater than 50 degrees C) alone is being used for selective tissue destruction as an alternative to conventional invasive surgery. The degree of thermal enhancement of these therapies is strongly dependent on the ability to localize and maintain therapeutic temperature elevations. Due to the often heterogeneous and dynamic properties of tissues, most notably blood perfusion and the presence of thermally significant blood vessels, therapeutic temperature elevations are difficult to spatially and temporally control during these forms of HT therapy. However, ultrasound technology has significant advantages that allow for a higher degree of spatial and dynamic control of the heating compared to other commonly utilized heating modalities. These advantages include a favorable range of energy penetration characteristics in soft tissue and the ability to shape the energy deposition patterns. Thus, heating systems have been developed for interstitial, intracavitary, or external approaches that utilize properties such as multiple transducer arrays, phased arrays, focused beams, mechanical and/or electrical scanning, dynamic frequency control and transducers of various shapes and sizes. This article provides a general review of a selection of ultrasound hyperthermia systems that are either in clinical use or currently under development, that utilize these advantages as a means to better localize and control HT for the aforementioned therapies.

Induction of hyperthermia using an intracavitary multielement ultrasonic applicator.

In this paper, the possibility of inducing controlled hyperthermia in rectal or vaginal wall tumors using an intracavitary ultrasonic applicator was investigated. A computer model that took into account the thermal and ultrasonic properties of tissues and surface cooling was used to optimize the transducer parameters to obtain desirable temperature distributions for different perfusion situations in the tumor. Also, an applicator that consisted of a cylindrical array of five independently controllable ultrasonic transducers was developed. This array was then tested in degassed water to determine the functional characteristics. This same applicator, modified to include water cooling of the tissue surface, was tested in vivo in dogs. The temperature distributions were found to be promising and with modifications this approach will be used in clinical treatments of suitable tumors.

Ultrasound applicators with internal water-cooling for high-powered interstitial thermal therapy.

Internal water-cooling of direct-coupled ultrasound (US) applicators for interstitial thermal therapy (hyperthermia and coagulative thermal therapy) was investigated. Implantable applicators were constructed using tubular US sources (360 angular acoustic emittance, approximately 7 MHz) of 10 mm length and 1.5, 1.8, 2.2, and 2.5 mm outer diameter (OD). Directional applicators were also constructed using 2.2 mm OD tubes sectored to provide active acoustic sectors of 90 degrees and 200 degrees. A water-cooling mechanism was integrated within the inner lumen of the applicator to remove heat from the inner transducer surface. High levels of convective heat transfer (2100-3800 W/m2K) were measured for practical water flow rates of 20-80 mL/min. Comparative acoustic measurements demonstrated that internal water-cooling did not significantly degrade the acoustic intensity or beam distribution of the US transducers. Water-cooling allowed substantially higher levels of applied electrical power (> 45 W) than previous designs (with air-cooling or no cooling), without detriment to the applicators. High-temperature heating trials performed with these applicators in vivo (porcine liver and thigh muscle) and in vitro (bovine liver) showed improved thermal penetration and coagulation. Radial depth of coagulation from the applicator surface ranged from 12 to 20 mm for 1-5 min of sonication with 28-W applied power. Higher powers (41 W) demonstrated increased coagulation depths (approximately 9 mm) at shorter times (15 s). Thermal lesion dimensions (angular and axial expanse) produced with directional applicators were controlled and directed, and corresponded to the active zone of the transducer. These characteristic lesion shapes were also generally unchanged with different sonication times and power, and were found to be consistent with previous coagulation studies using air-cooled applicators. The implementation of water-cooling is a significant advance for the application of ultrasound interstitial thermal therapy (USITT), providing greater treatment volumes, shorter treatment times, and the potential for treatment of highly perfused tissue with shaped lesions.

The role of physical exercise and inactivity in pain recurrence and absenteeism from work after active outpatient rehabilitation for recurrent or chronic low back pain: a follow-up study.

STUDY DESIGN: An observational follow-up. OBJECTIVES: To analyze the role of physical exercise and inactivity on the long-term outcome after active outpatient low back rehabilitation. SUMMARY OF BACKGROUND DATA: There is considerable evidence documenting the efficacy of exercise in the conservative treatment of chronic low back pain, but the role of exercises after the guided treatment period on the long-term success and maintenance of the results is not known. METHODS: One hundred twenty-five patients with low back pain, who had participated in a 12-week active low back rehabilitation program, were asked about subjective pain and disability on the average of 14 months after the treatment. The outcomes were defined as a recurrence of persistent pain and work absenteeism, and a survival or failure analysis was performed between those who had continued exercising and who had been physically inactive. RESULTS: Recurrences of persistent pain during the follow-up period were fewer (P = 0.03) among those who had maintained regular exercise habits after the treatment than among those who had been physically inactive. Similarly, work absenteeism was less (P < 0.01) among physically active than among physically inactive persons. However, patients with good outcome in pain reduction after low back pain rehabilitation were more likely to participate in physical exercise. CONCLUSIONS: Exercises are beneficial after guided treatment in the maintenance of the results of active treatment for recurrent chronic low back pain in the long term, but those with less favorable outcome in rehabilitation are less likely to participate in exercises afterward. In active treatment programs, it is recommended that exercises be incorporated after the guided treatment.

Acute biomechanical and histological effects of intradiscal electrothermal therapy on human lumbar discs.

STUDY DESIGN: Human cadaver lumbar spines were used to assess the acute effects of intradiscal electrothermal therapy in vitro. OBJECTIVE: To determine whether intradiscal electrothermal therapy produces acute changes in disc histology and motion segment stability. SUMMARY OF BACKGROUND DATA: Intradiscal electrothermal therapy has been introduced as an alternative for the treatment of discogenic low back pain. Several hypothesized mechanisms for the effect of intradiscal electrothermal therapy have been suggested including shrinkage of the nucleus or sealing of the anulus fibrosus by contraction of collagen fibers, and thermal ablation of sensitive nerve fibers in the outer anulus. METHODS: Intradiscal electrothermal therapy was performed with the Spinecath by Oratec on 19 fresh, frozen human lumbar cadaver specimens. In a separate study, eight specimens were tested biomechanically and instrumented to map the thermal distribution, whereas five specimens were tested only biomechanically, both before and after intradiscal electrothermal therapy. Six additional specimens were heated with intradiscal electrothermal therapy, and the resulting canal was backfilled with a silicone rubber compound to allow colocalization of the catheter and anular architecture. RESULTS: A consistent pattern of increased motion and decreased stiffness was observed. For the specimens in which only biomechanical measurements were taken, a 10% increase in the motion, on the average, at 5 Nm torque was observed after intradiscal electrothermal therapy. No apparent alteration of the anular architecture was observed around the catheter site in the intradiscal electrothermal therapy-treated discs. CONCLUSION: The data from this study suggest that the temperatures developed during intradiscal electrothermal therapy are insufficient to alter collagen architecture or stiffen the treated motion segment acutely.

The feasibility of using electrically focused ultrasound arrays to induce deep hyperthermia via body cavities.

The results of a simulation study and subsequent experimental verification on the feasibility of using electrically focused arrays for intracavitary ultrasound hyperthermia are presented. The relative acoustic pressure fields from these cylindrical phased arrays were calculated for different dimensions and acoustic parameters to determine relevant design criteria. A thermal model based on the bioheat transfer equation was used to compute the resulting steady-state temperature distributions in tissue for various array configurations. This study has shown that cylindrical arrays of a practical size (75 mm long, 15 mm OD), resonating at 0.5 MHz with individual elements that are 1.5-mm wide, can preferentially heat regions that are between 20 and 50 mm from the surface of the array. In addition, it was shown that the temperature distribution can be further controlled by varying the focal position within the target volume, producing heated regions up to 40 mm wide. If practical constraints (i.e. number of amplifiers available or minimum element size attainable) become a limiting factor, arrays with wider elements would also be functional, but with certain restrictions applied to their flexible heating patterns. Thus, these electrically focused ultrasound arrays appear to offer a significant improvement over the existing intracavitary hyperthermia methods by producing a deeper and more controlled energy deposition.