High-intensity Focused Ultrasound: Ready for Primetime

Recognition of Biological Tissue Denaturation Based on Improved Multiscale Permutation Entropy and GK Fuzzy Clustering

Recognition of biological tissue denaturation is a vital work in high-intensity focused ultrasound (HIFU) therapy. Multiscale permutation entropy (MPE) is a nonlinear signal processing method for feature extraction, widely applied to the recognition of biological tissue denaturation. However, the typical MPE cannot derive a stable entropy due to intensity information loss during the coarse-graining process. For this problem, an improved multiscale permutation entropy (IMPE) is proposed in this work. IMPE is obtained through refining and reconstructing MPE. Compared with MPE, the IMPE overcomes the deficiency of amplitude information loss due to the coarse-graining process when computing signal complexity. Through the simulation of calculating MPE and IMPE from white Gaussian noise, it is found that the entropy derived by IMPE is more stable than that derived by MPE. The processing method based on IMPE feature extraction is applied to the experimental ultrasonic scattered echo signals in HIFU treatment. Support vector machine and Gustafson–Kessel fuzzy clustering based on MPE and IMPE feature extraction are also used for biological tissue denaturation classification and recognition. The results calculated from the different combination algorithms show that the recognition of biological tissue denaturation based on IMPE-GK clustering is more reliable with the accuracy of 95.5%.

The Use of High-Intensity Focused Ultrasound (HIFU) Plus 150mg Bicalutamide as First Line Salvage Therapy for Local Recurrent Prostate Cancer

Patients with localized prostate cancer (PCa) are often treated with radical prostatectomy (RP). However, more than 30% of such patients have high risk of recurrence. Salvage radiotherapy (SRT), androgen deprivation therapy (ADT) and combination of radiotherapy and ADT are the standard care for recurrent PCa. Recently, high intensity focused ultrasound (HIFU) has gradually applied in the treatment of recurrent PCa. Here, we proposed a hypothesis that combined HIFU and bicalutamide 150mg as first line salvage therapy to treat patients with local recurrent PCa with visible lesions due to the following advantages: (1) HIFU is effective in reducing local tumor load, and bicalutamide 150mg is a feasible and safety option to combine with HIFU. (2) Compared with radiotherapy, HIFU plus 150mg bicalutamide is minimal invasiveness with fewer adverse effects and better quality of life(QOL); (3) Radiotherapy can be preserved as the second-line salvage method in the cases who are failure to HIFU and 150mg bicalutamide combination. More clinical trials are warranted to confirm this hypothesis in treatment with recurrent PCa.

An Introduction to High Intensity Focused Ultrasound: Systematic Review on Principles, Devices, and Clinical Applications

Ultrasound can penetrate deep into tissues and interact with human tissue via thermal and mechanical mechanisms. The ability to focus an ultrasound beam and its energy onto millimeter-size targets was a significant milestone in the development of therapeutic applications of focused ultrasound. Focused ultrasound can be used as a non-invasive thermal ablation technique for tumor treatment and is being developed as an option to standard oncologic therapies. High-intensity focused ultrasound has now been used for clinical treatment of a variety of solid malignant tumors, including those in the pancreas, liver, kidney, bone, prostate, and breast, as well as uterine fibroids and soft-tissue sarcomas. Magnetic resonance imaging and Ultrasound imaging can be combined with high intensity focused ultrasound to provide real-time imaging during ablation. Magnetic resonance guided focused ultrasound represents a novel non-invasive method of treatment that may play an important role as an alternative to open neurosurgical procedures for treatment of a number of brain disorders. This paper briefly reviews the underlying principles of HIFU and presents current applications, outcomes, and complications after treatment. Recent applications of Focused ultrasound for tumor treatment, drug delivery, vessel occlusion, histotripsy, movement disorders, and vascular, oncologic, and psychiatric applications are reviewed, along with clinical challenges and potential future clinical applications of HIFU.

Partial Gland Treatment of Prostate Cancer Using High-Intensity Focused Ultrasound in the Primary and Salvage Settings: A Systematic Review

PURPOSE

Advances in prostate imaging, biopsy and ablative technologies have been accompanied by growing enthusiasm for partial gland ablation, particularly using high-intensity focused ultrasound, to treat prostate cancer. Preserving noncancerous prostate tissue and minimizing damage to the neurovascular bundles and external urethral sphincter may improve functional outcomes.

MATERIALS AND METHODS

A systematic review was performed following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines using a combination of MeSH® terms, free text search and examination of relevant bibliographies using MEDLINE® and Embase® from the inception of each database through October 10, 2016. We excluded studies describing exclusively whole gland ablation, case reports and series where treatment was followed by immediate resection.

RESULTS

A total of 13 studies that enrolled 543 patients were included. Of the studies 11 were performed in the primary setting and 2 in the salvage setting. Median followup ranged from 6 months to 10.6 years. Rates of posttreatment erectile dysfunction and urinary incontinence ranged from 0% to 48% and 0% to 50%, respectively, with definitions varying by study. Overall there were 254 reported complications. Marked heterogeneity between studies limited the ability to pool results regarding functional and oncologic outcomes. A total of 76 patients (14%) subsequently received further oncologic treatment.

CONCLUSIONS

Early evidence suggests that partial gland ablation is a safe treatment option for men with localized disease. Longer term data are needed to evaluate oncologic efficacy and functional outcomes, and will aid in identifying the optimal candidates for therapy. Standardization of outcomes definitions will allow for better comparison between studies and among treatment modalities.

Simulation of thermal ablation by high-intensity focused ultrasound with temperature-dependent properties

An integrated computational framework was developed in this study for modeling high-intensity focused ultrasound (HIFU) thermal ablation. The temperature field was obtained by solving the bioheat transfer equation (BHTE) through the finite element method; while, the thermal lesion was considered as a denatured material experiencing phase transformation and modeled with the latent heat. An equivalent attenuation coefficient, which considers the temperature-dependent properties of the target material and the ultrasound diffraction due to bubbles, was proposed in the nonlinear thermal transient analysis. Finally, a modified thermal dose formulation was proposed to predict the lesion size, shape and location. In-vitro thermal ablation experiments on transparent tissue phantoms at different energy levels were carried out to validate this computational framework. The temperature histories and lesion areas from the proposed model show good correlation with those from the in-vitro experiments.

Salvage HIFU for biopsy confirmed local prostate cancer recurrence after radical prostatectomy and radiation therapy: Case report and literature review

High-intensity focused ultrasound (HIFU) is a treatment option for low- and intermediate-risk prostate cancer and more recently has been used as salvage therapy after failed radiation therapy. We present a case of local recurrence with biochemical failure after radical prostatectomy and salvage external beam radiation therapy with salvage HIFU without biochemical recurrence at 20 months.

Metabolic syndrome and lower urinary tract symptoms: the role of inflammation

BACKGROUND

Epidemiological data indicate that lower urinary tract symptoms (LUTS)/BPH can be associated with metabolic syndrome (MetS). Chronic inflammation has been proposed as a candidate mechanism at the crossroad between these two clinical entities.Aim of study is to examine the correlation among pre-operatory LUTS/BPH severity, MetS features and inflammatory infiltrates in prostatectomy specimens.

METHODS

A total of 271 consecutive men treated with simple prostatectomy were retrospectively selected for this study in two tertiary referral centers for LUTS/BPH. Prostate diameters and volume were measured by transrectal ultrasound, LUTS scored by International Prostate Symptom Score (IPSS) and obstruction by uroflowmetry. The International Diabetes Federation and American Heart Association and the National Heart, Lung and Blood Institute was used to define MetS. The inflammatory infiltrate was investigated combining anatomic location, grade and extent of flogosis into the overall inflammatory score (IS); the glandular disruption (GD) was used as a further marker.

RESULTS

Eighty-six (31.7%) men were affected by MetS. Prostatic volume and anterior-posterior (AP) diameter were positively associated to the number of MetS components. Among MetS determinants, only dyslipidaemia (increased serum triglycerides and reduced serum high-density lipoprotein) was associated with an increased risk of having a prostatic volume >60 cm(3) (hazard ratio (HR) = 3.268, P < 0.001). A significant positive correlation between the presence of MetS and the IS was observed. MetS patients presented lower uroflowmetric parameters as compared with those without MetS (Maximum flow rate (Q(max)): 8.6 vs 10.1, P = 0.008 and average flow rate (Q(ave)): 4.6 vs 5.3, P = 0.033, respectively), and higher obstructive urinary symptoms score (P = 0.064). A positive correlation among both IS-GD and IPSS Score was also observed (adjusted r = 0.172, P = 0.008 and adjusted r = 0.128, P = 0.050).

CONCLUSIONS

MetS is associated with prostate volume, prostatic AP diameter and intraprostatic IS. The significantly positive association between MetS and prostatic AP diameter could support the observation that MetS patients presented lower uroflowmetric parameters. In conclusion, MetS can be regarded as a new determinant of prostate inflammation and BPH progression.

Considerations for theoretical modelling of thermal ablation with catheter-based ultrasonic sources: implications for treatment planning, monitoring and control

PURPOSE

To determine the impact of including dynamic changes in tissue physical properties during heating on feedback controlled thermal ablation with catheter-based ultrasound. Additionally, we compared the impact of several indicators of thermal damage on predicted extents of ablation zones for planning and monitoring ablations with this modality.

METHODS

A 3D model of ultrasound ablation with interstitial and transurethral applicators incorporating temperature-based feedback control was used to simulate thermal ablations in prostate and liver tissue. We investigated five coupled models of heat dependent changes in tissue acoustic attenuation/absorption and blood perfusion of varying degrees of complexity. Dimensions of the ablation zone were computed using temperature, thermal dose, and Arrhenius thermal damage indicators of coagulative necrosis. A comparison of the predictions by each of these models was illustrated on a patient-specific anatomy in the treatment planning setting.

RESULTS

Models including dynamic changes in blood perfusion and acoustic attenuation as a function of thermal dose/damage predicted near-identical ablation zone volumes (maximum variation < 2.5%). Accounting for dynamic acoustic attenuation appeared to play a critical role in estimating ablation zone size, as models using constant values for acoustic attenuation predicted ablation zone volumes up to 50% larger or 47% smaller in liver and prostate tissue, respectively. Thermal dose (t(43) ≥ 240 min) and thermal damage (Ω ≥ 4.6) thresholds for coagulative necrosis are in good agreement for all heating durations, temperature thresholds in the range of 54°C for short (<5 min) duration ablations and 50°C for long (15 min) ablations may serve as surrogates for determination of the outer treatment boundary.

CONCLUSIONS

Accounting for dynamic changes in acoustic attenuation/absorption appeared to play a critical role in predicted extents of ablation zones. For typical 5-15 min ablations with this modality, thermal dose and Arrhenius damage measures of ablation zone dimensions are in good agreement, while appropriately selected temperature thresholds provide a computationally cheaper surrogate.

Overview of therapeutic ultrasound applications and safety considerations

Applications of ultrasound in medicine for therapeutic purposes have been accepted and beneficial uses of ultrasonic biological effects for many years. Low-power ultrasound of about 1 MHz has been widely applied since the 1950s for physical therapy in conditions such as tendinitis and bursitis. In the 1980s, high-pressure-amplitude shock waves came into use for mechanically resolving kidney stones, and "lithotripsy" rapidly replaced surgery as the most frequent treatment choice. The use of ultrasonic energy for therapy continues to expand, and approved applications now include uterine fibroid ablation, cataract removal (phacoemulsification), surgical tissue cutting and hemostasis, transdermal drug delivery, and bone fracture healing, among others. Undesirable bioeffects can occur, including burns from thermal-based therapies and severe hemorrhage from mechanical-based therapies (eg, lithotripsy). In all of these therapeutic applications of ultrasound bioeffects, standardization, ultrasound dosimetry, benefits assurance, and side-effect risk minimization must be carefully considered to ensure an optimal benefit to risk ratio for the patient. Therapeutic ultrasound typically has well-defined benefits and risks and therefore presents a manageable safety problem to the clinician. However, safety information can be scattered, confusing, or subject to commercial conflicts of interest. Of paramount importance for managing this problem is the communication of practical safety information by authoritative groups, such as the American Institute of Ultrasound in Medicine, to the medical ultrasound community. In this overview, the Bioeffects Committee of the American Institute of Ultrasound in Medicine outlines the wide range of therapeutic ultrasound methods, which are in clinical use or under study, and provides general guidance for ensuring therapeutic ultrasound safety.

A comparative evaluation of three hydrophones and a numerical model in high intensity focused ultrasound fields

The pressure fields of two different high intensity focused ultrasound (HIFU) transducers operated in burst mode were measured at acoustical power levels of 25 and 50 W (continuous wave equivalent) with three different hydrophones: A fiber-optic displacement sensor, a commercial HIFU needle hydrophone, and a prototype of a membrane hydrophone with a protective coating against cavitation effects. Additionally, the fields were modeled using a freely available simulations software package. The measured waveforms, the peak pressure profiles, as well as the spatial-peak temporal-average intensities from the different devices and from the modeling are compared and possible reasons for differences are discussed. The results clearly show that reliable pressure measurements in HIFU fields remain a difficult task concerning both the reliability of the measured values and the robustness of the sensors used: Only the fiber-optic hydrophone survived all four exposure regimes and the measured spatial-peak temporal-average intensities varied by a factor of up to 1.5 between the measurements and the modeling and between the measurements among themselves.

Characterization of a fiber-optic displacement sensor for measurements in high-intensity focused ultrasound fields

A fiber-optic sensor is presented that is capable of measuring the particle displacement in high-intensity focused ultrasound (HIFU) fields. For this probe, a secondary calibration was performed, and the resulting complex frequency response is discussed. As a first practical application, the setup was used to measure the pressure in the field of a weakly focusing ultrasound transducer. The result is compared with that of a membrane hydrophone measurement. The feasibility of measurements in HIFU fields is demonstrated by means of measurements of the spatial distribution of the peak particle velocity within the focus of a HIFU transducer and of the dependence of the peak values on the acoustical power level.

The future of pediatric US

Despite advances in other modalities, US remains an essential technology in pediatric imaging. Improvements in technology provide increasingly detailed anatomical images, and new techniques show promise in providing novel anatomical as well as physiological and structural information. Other specialties are recognizing the value of US to their patients and are increasingly performing their own examinations. Economic and social factors are also influencing the development and use of US. This review will evaluate many of these issues and demonstrate that the future of pediatric US is bright and that pediatric radiologists can and should continue to be leaders in its use and development.

Benign prostatic hyperplasia and prostate cancer: an overview for primary care physicians

Benign prostatic hyperplasia (BPH) and prostate cancer (CaP) are major sources of morbidity in older men. Management of these disorders has evolved considerably in recent years. This article provides a focused overview of BPH and CaP management aimed at primary care physicians. Current literature pertaining to BPH and CaP is reviewed and discussed. The management of BPH has been influenced by the adoption of effective medical therapies; nonetheless, surgical intervention remains a valid option for many men. This can be accomplished with well-established standards such as transurethral resection of the prostate or with minimally invasive techniques. Prostate cancer screening remains controversial despite the recent publication of two large clinical trials. Not all prostate cancers necessarily need to be treated. Robot-assisted prostatectomy is a new and increasingly utilised technique for CaP management, although open radical retropubic prostatectomy is the oncological reference standard. The ageing of the population of the developed world means that primary care physicians will see an increasing number of men with BPH and CaP. Close collaboration between primary care physicians and urologists offers the key to successful management of these disorders.