High intensity focused ultrasound: surgery of the future?

For 50 years, high intensity focused ultrasound (HIFU) has been a subject of interest for medical research. HIFU causes selective tissue necrosis in a very well defined volume, at a variable distance from the transducer, through heating or cavitation. Over the past decade, the use of HIFU has been investigated in many clinical settings. This literature review aims to summarize recent advances made in the field. A Medline-based literature search (1965-2002) was conducted using the keywords "HIFU" and "high intensity focused ultrasound". Additional literature was obtained from original papers and published meeting abstracts. The most abundant clinical trial data comes from studies investigating its use in the treatment of prostatic disease, although early research looked at applications in neurosurgery. More recently horizons have been broadened, and the potential of HIFU as a non-invasive surgical tool has been demonstrated in many settings including the treatment of tumours of the liver, kidney, breast, bone, uterus and pancreas, as well as conduction defects in the heart, for surgical haemostasis, and the relief of chronic pain of malignant origin. Further clinical evaluation will follow, but recent technological development suggests that HIFU is likely to play a significant role in future surgical practice.     

Thermal ablation of thyroid nodules: are radiofrequency ablation,microwave ablation and high intensity focused ultrasound equally safe and effective methods?

Objectives

This study compares volume reduction of benign thyroid nodules three months after Radiofrequency Ablation (RFA), Microwave Ablation (MWA) or High Intensity Focused Ultrasound (HIFU) to evaluate which of these methods is the most effective and safe alternative to thyroidectomy or radioiodine therapy.

Material and Methods

Ninety-four patients (39 male, 55 female) with a total of 118 benign, symptomatic thyroid nodules were divided into three subgroups. HIFU was applied to 14 patients with small nodules. The other 80 patients were divided up into two groups of 40 patients each for RFA and MWA in the assumption that both methods are comparable effective. The pre-ablative and post-ablative volume was measured by ultrasound.

Results

RFA showed a significant volume reduction of nodules of 50 % (p<0.05), MWA of 44 % (p<0.05) and HIFU of 48 % (p<0.05) three months after ablation. None of the examined ablation techniques caused serious or permanent complications.

Conclusion

RFA, MWA and HIFU showed comparable results considering volume reduction. All methods are safe and effective treatments of benign thyroid nodules.

Key Points

? Thermal Ablation can be used to treat benign thyroid nodules ? Thermal Ablation can be an alternative to thyroidectomy or radioiodine therapy ? Radiofrequency Ablation, Microwave Ablation, High Intensity Focused Ultrasound are safe and effective

     

HIRE (high intensity reduction) Neue liquorunterdrückte, T2-gewichtete Bildgebungssequenz

Purpose. The HIRE sequence utilizes the very long T2 value of CSF to suppress its high signal contribution in T2-weighted imaging by an image subtraction technique. Methods. To assess the diagnostic potential of a new dark fluid sequence HIRE (High Intensity REduction) in the diagnostic work-up, 20 patients with histologically confirmed cerebral gliomas were examined with T2-weighted FSE, T1-weighted SE, fast FLAIR and HIRE using identical scan parameters. In patients with enhancing lesions fast FLAIR and HIRE were added to the contrast-enhanced T1-weighted SE images. Images were analyzed in a qualitative and quantitative evaluation. In the qualitative lesion analysis, lesion delineation and differentiation between enhancing and non enhancing tumor tissue were by two readers. For the quantitative analysis lesion-to-background and lesion-to-CSF contrast and contrast to noise ratios were determined in an region of interest analysis. Results. HIRE achieved a significant reduction of the CSF signal without loosing the high gray-to-white matter contrast of T2 weighted sequences. In the quantitative analysis, the contrast ratios of the HIRE were lower compared to the FLAIR images due to a relative high background and CSF signal. After the application of contrast media HIRE images revealed a significant signal increase in enhancing lesions, which subsequently increased the contrast and contrast-to-noise ratios. In the qualitative analysis, both readers found all tumors clearly delineated on HIRE imaging. Compared to T2-weighted FSE the tumor delineation with HIRE was better in nine patients, equal in four patients and less in one patient. Compared to the FLAIR images HIRE was rated superior in three patients, equal in nine patients and inferior in another three patients. Delineation of the enhancing tumor parts was possible with HIRE in all patients. HIRE images present significant less image artifacts than FLAIR images due to reduced inflow effects. Conclusions. The presented T₂ based HIRE sequence is an alternative to the T₁ based FLAIR sequence with the advantage of a better gray to white matter contrast and shorter measurement time. Due to the subtraction technique signal intensities from tissues with T2 relaxation times in the range between white matter and CSF are also partially affected depending on their T₂ values. With respect to this undesired effect, an improvement in HIRE imaging will be expected by a self-weighted subtraction algorithm.     

Does the phase of menstrual cycle affect MR-guided focused ultrasound surgery of uterine leiomyomas?

PURPOSE: To determine whether the phase of menstrual cycle at the time of MR-guided focused ultrasound surgery (MRgFUS) treatment for uterine leiomyomas affects treatment outcome. METHODS: We enrolled all patients participating in a prospective phase III clinical trial from our center who completed 6 months of clinical and imaging follow-up. Patients with irregular cycles and those on oral contraceptives were excluded. Data prospectively documenting the date of the last menstrual period (LMP) at the time of treatment, length and duration of cycle, and raw symptom severity score (SSS) from the Uterine Fibroid Symptom and Quality of Life questionnaire, at baseline and 6 months were collected. Proliferative phase patients were determined retrospectively as those who were treated within less than 14 days from LMP; secretory phase patients were classified as those who were treated greater than 14 days from LMP. RESULTS: A total of 58 patients were enrolled. There was no significant difference in the mean SSS at baseline and mean SSS at 6 months between patients treated in the proliferative versus secretory phase of the cycle. No significant difference in the SSS change from baseline to 6 months was seen between the two groups. CONCLUSIONS: Menstrual cycle phase does not influence MRgFUS treatment outcome. Symptomatic improvement occurs with treatment during either phase of the menstrual cycle. Thus, the scheduling of MRgFUS treatment need not be based upon the phase of the menstrual cycle.     

High-intensity focused ultrasound ablation of liver tumours: can radiological assessment predict the histological response?

Cancer therapies usually depend on cross-sectional imaging for the assessment of treatment response. This study was designed to evaluate the ability of MRI to predict zones of necrosis following the use of high-intensity focused ultrasound (HIFU) to treat liver metastases. Patients with liver metastases, who had been scheduled for elective surgical resection of their tumours, were recruited to this non-randomized Phase II study. In each case, a proportion of an index liver tumour target was ablated. The response to HIFU was assessed after 12 days using contrast-enhanced MRI and compared directly with histological analysis at the time of surgery. Eight patients were treated, of whom six were subsequently assessed with both MRI and histology. There were no major complications. MRI predicted complete ablation in three cases. In each case, histological analysis confirmed complete ablation. In one case, the region of ablation observed on MRI appeared smaller than predicted at the time of HIFU, but histology revealed complete ablation of the target region. The predominant characteristic of HIFU-ablated tissue was coagulative necrosis but heat fixation was evident in some areas. Heat-fixed cells appeared normal under haematoxylin and eosin staining, indicating that this is unreliable as an indicator of HIFU-induced cell death. This study demonstrates that HIFU is capable of achieving selective ablation of pre-defined regions of liver tumour targets, and that MRI evidence of complete ablation of the target region can be taken to infer histological success.     

MRI-guided focused ultrasound (MRgFUS) to treat facet joint osteoarthritis low back pain—case series of an innovative new technique

European Radiology - To evaluate the safety and efficacy of magnetic resonance-guided focused ultrasound (MRgFUS) to treat facet joint osteoarthritis pain. Patients with a positive response to...     

Development of a high intensity 192Ir γ-ray radiographic source

The method of preparing an intensive ¹⁹²Ir γ-ray radiographic source developed in Japan Atomic Energy Research Institute is described. In the method, neutron self-shielding during the irradiation can be avoided. To produce a source of more than 100 Ci in equivalent activity, thin iridium discs 3 mm dia. and 0.4 mm thick are irradiated at neutron flux densities of several 10¹⁴n/cm².sec, for about 2 or 3 week; after the irradiation the activated discs are assembled into a source capsule. The experimental results on the equivalent activity of the ¹⁹²Ir sources produced agree well with the calculated results. A radiographic irradiator for the source of about 100 Ci is also described.     

Correlations between the time–intensity parameters of contrast-enhanced ultrasound and clinical prognosis of hepatocellular carcinoma

PurposeThe purpose of the study was to detect the correlation between the time–intensity parameters of contrast-enhanced ultrasound (CEUS) and the clinical prognosis of hepatocellular carcinoma (HCC).MethodsA total of 73 HCC patients were analyzed with the time–intensity curve of CEUS. The expression of vascular endothelial factor (VEGF) and CD34 in different differentiation-staged HCC specimens was observed using immunohistochemistry.ResultsA positive correlation was found between the VEGF expression and microvessel density. The time–intensity parameters were not correlated with the HCC size.ConclusionsCEUS time–intensity parameters are inducive for assessing the prognosis of HCC with revealed intratumoral microvessel perfusion in different differentiation stages.     

Uterine fibroids: Influence of “T2-Rim sign” on immediate therapeutic responses to magnetic resonance imaging-guided high-intensity focused ultrasound ablation

ObjectivesTo investigate the influence of a high-signal-intensity peripheral rim on T2-weighted MR images (i.e., T2-rim sign) on the immediate therapeutic responses of MR-guided high intensity focused ultrasound (MR-HIFU) ablation of uterine fibroids.MethodsThis retrospective study was approved by the institutional review board, and patient informed consent was obtained for MR-HIFU ablation. In total, 196 fibroids (diameter 6.2 ± 2.6 cm) in 123 women (age 43.4 ± 5.0 years) who underwent MR-HIFU ablation from January 2013 to April 2016 were included. The effects of a T2-rim sign on the immediate therapeutic responses (non-perfused volume [NPV] ratio, ablation efficiency [NPV/treatment cell volume], ablation quality [grade 1-5, poor to excellent]) were investigated with univariable and multivariable analyses using generalized estimating equation (GEE) analysis. In multivariable analysis, T2 signal intensity ratio of fibroids-to-skeletal muscle, relative peak enhancement of fibroids, and subcutaneous fat thickness were also considered.ResultsThe presence of a T2-rim sign significantly lowered the NPV ratio (54.0 ± 28.0% vs. 83.7 ± 17.7%), ablation efficiency (0.6 ± 0.5 vs. 1.3 ± 0.6), ablation quality (3.1 ± 1.2 vs. 4.2 ± 0.8), (P < 0.0001). GEE analysis showed that the presence of a T2-rim sign was independently significant for ablation efficiency and ablation quality (P < 0.05).ConclusionUterine fibroids with a T2-rim sign showed significantly poorer immediate therapeutic responses to MR-HIFU ablation.     

Is point-of-care ultrasound disruptive innovation? Formulating why POCUS is different from conventional comprehensive ultrasound

Background

Point-of-care ultrasound (PoCUS) is spreading throughout Emergency Medicine, Critical Care and Pre-hospital Care. However, there is an underlying inherited conflict with the established specialties performing comprehensive examinations. It has been stated that PoCUS is disruptive innovation. If this is true the definition might open up for a new perspective on differentiating comprehensive ultrasound from PoCUS. PoCUS in the light of disruptive innovation is a different perspective on ultrasound that has not before been academically scrutinized.

Methods

In this paper we investigate if PoCUS is in fact disruptive innovation. This is done by comparative analysis with the point of departure in disruptive innovation theory known from the business world.

Results

We find that a disruptive innovation process is happening. This new knowledge allows us to put forward advice for the stakeholders in the field of ultrasound. It also allows us to challenge the conventional pyramid of expertise used to describe different types of ultrasound. The perspective of this paper is mutual understanding of similarities and differences between conventional and point-of-care ultrasound. Only with this understanding the stakeholders can collaborate and use the full spectrum of ultrasound for the benefit of the patient.

     

Imaging the premature brain: ultrasound or MRI?

Neuroimaging of preterm infants has become part of routine clinical care, but the question is often raised on how often cranial ultrasound should be done and whether every high risk preterm infant should at least have one MRI during the neonatal period. An increasing number of centres perform an MRI either at discharge or around term equivalent age, and a few centres have access to a magnet in or adjacent to the neonatal intensive care unit and are doing sequential MRIs. In this review, we try to discuss when best to perform these two neuroimaging techniques and the additional information each technique may provide.     

Can ultrasound help to define orthopedic surgical complications?

This article aims to describe and illustrate the usefulness of ultrasound in detecting complications of orthopedic implants, metal fixation devices, and other surgical material, with an emphasis on soft-tissue pathology.     

Chronic hypersensitivity pneumonitis or idiopathic pulmonary fibrosis? Diagnostic role of high resolution Computed Tomography (HRCT)

PURPOSE: In the diagnosis of extrinsic allergic alveolitis, high-resolution computed tomography (HRCT) is more sensitive and more specific than radiography; however, the accuracy of HRCT is not absolute. The role of HRCT in this field has scarcely been investigated in the literature. The purpose of this paper is to explore the possibilities of HRCT in this field and to analyse the correlations between HRCT and functional parameters. MATERIALS AND METHODS: We performed a retrospective blind evaluation the HRCT scans of 24 patients (19 males and 5 females). Twelve were affected by idiopathic pulmonary fibrosis (IPF); 12 had chronic extrinsic allergic alveolitis (EAA) or hypersensitivity pneumonitis. The HRCT findings were studied by two radiologists, who were not aware of the diagnoses. The possible differences in evaluation were subsequently resolved by consensus. In the presence of interstitial fibrosis, we recorded the prevailing site and the anatomical extension (with the method of the visual percentage score, described in the literature). In all the cases, we recorded the blood gas values (PaO2, PaCO2, and pH), total lung capacity (TLC), forced expiratory volume in 1 second (FEV1), Vital Capacity (VC), Tiffeneau index (FEV1/VC) and monoxide carbon diffusion (DLCO). The statistical significance of the correlations was investigated using the Mann-Whitney and Wilcoxon tests. Student "t"-test and Pearson's chi squared were used to compare the variables of the different groups. A value of p< or =0.05 was considered significant. RESULTS: Overall, the diagnosis was formulated with a high degree of confidence in 13 of 24 cases (54.1%); in these patients, the result was correct in 84.6% of cases (11 of 13). In the diagnosis of EAA, HRCT sensitivity was 50%, with 91.6% specificity, 70.8% accuracy. In the diagnosis of IPF, HRCT sensitivity was 75%, with 83.3% specificity, 79.1% accuracy. The HRCT signs of interstitial fibrosis were visible in 11 cases of IPF (91.6%) and in 4 cases of EAA (33.3%), with significant statistical difference (p<0.005). In the analysis of the whole series (24 patients) we found a significant inverse correlation between the HRCT score of fibrosis and the extension of the areas with air-trapping (p<0.003). There was no significant difference between IPF and EAA considering age, FEV1, PaO2, PaCO2 and pH. We found inverse correlation (p<0.001) between HRCT extension of the fibrosis and DLCO. There was a significant difference between pulmonary fibrosis and extrinsic allergic alveolitis considering TLC (in average, respectively: 65% and 84.3%; p<0.02), and DLCO (respectively 40.4% and 74.7%; p<0.03). DISCUSSION AND CONCLUSIONS: HRCT is a reliable and strong method to be used in particularly complex fields. We found signs of interstitial fibrosis more frequently in IPF than in EAA (91.6% versus 33.3%). In IPF cases, the extension of the fibrosis--evaluated with the visual score method--was higher then in EAA (34.7% versus 6%). The presence of fibrosis with basal and peripheral distribution was characteristic of idiopathic pulmonary fibrosis, with good sensitivity and specificity (75%), whereas in chronic extrinsic allergic alveolitis the areas of fibrosis often presented an irregular and heterogeneous distribution, in 91.6% of cases. However, 25% of extrinsic allergic alveolitis cases had a distribution mimicking idiopathic pulmonary fibrosis. The presence of areas with increased ground-glass opacity is more common in EAA than in IPF (66.6% versus 33.3%). Areas of mosaic attenuation, visible in inspiratory CT scans, are not rare in IPF (41.6% of cases), and generally have a basal distribution. The presence of hyperlucent lobules inside the fibrotic areas does not exclude the diagnosis of IPF. The finding of the expiratory air-trapping is more common in chronic EAA than in IPF, and the extension of this areas is greater in EAA (17.3% versus 6.5%). We found an inverse correlation between the extension of the fibrosis and the expiratory trapping. Signs of emphysema were observed in 25% of cases, wiema were observed in 25% of cases, with equal prevalence and the same extension in IPF and in EAA. All patients were smokers or ex-smokers. Smoking has not been demonstrated to have a protective effect against EAA. The areas of mosaic perfusion during inspiration do not represent a sound criterion for the differential diagnosis between IPF and chronic EAA. In fact, they can also be frequently found in IPF. HRCT can be employed in clinical practice for the differential diagnosis between IPF and chronic EAA with good (but not absolute) accuracy.