Is Ultrasound Fusion a Reasonable Replacement for Computed Tomography in Guiding Abdominal Interventions?

Deep regression 2D-3D ultrasound registration for liver motion correction in focal tumour thermal ablation

Liver tumour ablation procedures require accurate placement of the needle applicator at the tumour centroid. The lower-cost and real-time nature of ultrasound (US) has advantages over computed tomography for applicator guidance, however, in some patients, liver tumours may be occult on US and tumour mimics can make lesion identification challenging. Image registration techniques can aid in interpreting anatomical details and identifying tumours, but their clinical application has been hindered by the tradeoff between alignment accuracy and runtime performance, particularly when compensating for liver motion due to patient breathing or movement. Therefore, we propose a 2D-3D US registration approach to enable intra-procedural alignment that mitigates errors caused by liver motion. Specifically, our approach can correlate imbalanced 2D and 3D US image features and use continuous 6D rotation representations to enhance the model's training stability. The dataset was divided into 2388, 196, and 193 image pairs for training, validation and testing, respectively. Our approach achieved a mean Euclidean distance error of2.28 m m ± 1.81 m m and a mean geodesic angular error of ± , with a runtime of0.22 s per 2D-3D US image pair. These results demonstrate that our approach can achieve accurate alignment and clinically acceptable runtime, indicating potential for clinical translation.

Ultrasound Fusion: Applications in Musculoskeletal Imaging

Ultrasound fusion is an established technique that pairs real time B-scan ultrasound (US) with other forms of cross-sectional imaging, including computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET). Each of these imaging modalities has distinct advantages. CT provides superior anatomic resolution, with improved imaging of bone and calcified structures; MRI has superior contrast resolution; and PET provides physiologic information, identifying processes that are metabolically active (i.e., tumor, inflammatory conditions). However, these modalities are static. A key highlight of ultrasound is its capability of dynamic, real-time scanning. The ability to pair CT, MRI or PET with ultrasound can have significant advantages, both in diagnostic evaluation and when performing difficult or challenging image-guided interventions. Percutaneous interventions using ultrasound fusion have been described in the abdominal imaging literature; however, there have been very few musculoskeletal applications detailed in the literature. The purpose of this article is to review the basic concepts of real-time ultrasound fusion, and to detail, through the use of multiple case examples, its potential use as a safe and effective method for performing image-guided musculoskeletal interventions.

PET/CT Ultrasound Fusion for Percutaneous Biopsy: A Retrospective Single-Center Study and Review of the Literature

PURPOSE

The aim of this study was to assess the diagnostic yield and complication rate of 18 F-FDG PET/CT ultrasound (US) fusion for percutaneous biopsy of FDG-avid lesions among patients with known or suspected malignancy.

PATIENTS AND METHODS

We describe the clinical, imaging, and histopathologic features of 36 patients who underwent percutaneous biopsy using real-time PET/CT US fusion. In addition, we review the literature on PET/CT US fusion. Using Medline, the following MeSH terms were searched and relevant citations assessed: "fusion imaging," "PET/CT fusion," "PET/CT-guided biopsy," "PET/US fusion," "ultrasound fusion," and "ultrasound fusion-guided biopsy."

RESULTS

A total of 36 patients (15 men, 21 women) with known or suspected malignancy and prior PET/CT imaging underwent percutaneous biopsy of FDG-avid lesions using PET/CT US fusion between October 2014 and July 2020. Coregistration was achieved using General Electric LOGIQ E9 software. Adequate tissue for analysis was obtained in all 36 patients. Histologic evaluation revealed malignancy in 14 patients (38.9%) and nonneoplastic tissue in 22 patients (61.1%). No intraprocedural or postprocedural complications were recorded.

CONCLUSIONS

Fusion of PET/CT and US for percutaneous biopsy of FDG-avid lesions can be used to achieve excellent diagnostic yield with a low risk of complications.

Lumbar nerve root blocks using MRI - the effectiveness and safety of ultrasound/MRI fusion image guidance

OBJECTIVE

To compare the outcome of nerve root injection guided by ultrasound/MRI fusion with radiofrequency needle tracking (eTRAX^©) and the same procedure undertaken by fluoroscopic guidance.

METHODS

This is a retrospective audit of anonymised clinical records from before and after a change in the imaging technique used to perform nerve root blocks.We studied 181 consecutive patients who had undergone a nerve root block, the first 124 guided by fluoroscopic technique and the next 57 guided by ultrasound/MRI fusion with radiofrequency needle guidance.Using pain diaries, we reviewed the outcome scores at 24 h and 2 weeks. We recorded the use of analgesia, the patient's satisfaction, complications and the duration of the procedures.

RESULTS

Completed pain diaries were returned by 61% in the fluoroscopy group and 67% in the fusion imaging group.The visual analogue pain score was reduced at 24 h by 3.29 [standard deviation (SD) 2.35] for the fluoroscopy group and by 3.69 (SD 2.58) in the fusion group (p 0.399).At two weeks the pain reduction was 3.27 (SD 2.57) for the fluoroscopic group and 4.21 (SD 2.95) for the fusion group (p 0.083). There was no statistically significant difference between the groups.The patient's satisfaction scores were similar for both groups.The procedure by the two guidance methods took a similar time to perform.There were no serious complications in either group. One patient in the fusion-guided nerve root block group experienced paraesthesia in the nerve distribution for 2 h.

CONCLUSION

Ultrasound/MRI fusion imaging with needle tracking is an effective alternative to fluoroscopic image-guided injection.

ADVANCES IN KNOWLEDGE

Fusion imaging guidance provides the same outcome as fluoroscopic guidance.Fusion imaging guidance avoids the need for ionising radiation.

Current role of ultrasound in the diagnosis of hepatocellular carcinoma

Ultrasonography (US) is a major, sustainable hepatocellular carcinoma (HCC) surveillance method as it provides inexpensive, real-time, and noninvasive detection. Since US findings are based on pathological features, knowledge of pathological features is essential for delivering a correct US diagnosis. Recent advances in US equipment have made it possible to provide more information, such as malignancy potential and accurate localization diagnosis of HCC. Evaluation of malignancy potential is important to determine the treatment strategy, especially for small HCC. Diagnosis of blood flow dynamics using color Doppler and contrast-enhanced US is one of the most definitive approaches for evaluating HCC malignancy potential. Recently, a new Doppler microvascular imaging technique, superb microvascular imaging, which can detect Doppler signals generated by low-velocity blood flow, was developed. A fusion imaging system, another innovative US technology, has already become an indispensable technology over the last few years not only for US-guided radiofrequency ablation but also for the detection of small, invisible HCC. This article reviews the evidence on the use of ultrasound and contrast-enhanced ultrasound with Sonazoid for the practical management of HCC.

Biopsy of Deep Pelvic and Abdominal Targets With Ultrasound Guidance: Efficacy of Compression

OBJECTIVE. The purpose of this study was to evaluate the utility of compression of tissues with the ultrasound transducer in decreasing distance to the biopsy target and establishing a safe percutaneous biopsy route to deep abdominopelvic targets. MATERIALS AND METHODS. Ultrasound-guided biopsies of nonsolid organ abdominopelvic targets performed from 2006 to 2017 were reviewed. Skin-to-target distance was measured on preprocedure CT scans for reference standard and on procedure ultrasound images for actual real-time distance after compression. The skin-to-target CT distance groupings were 0-3 cm, 3-6 cm, 6-10, cm, and > 10 cm. Deep targets were defined as > 6 cm. Differences in skin-to-target distance between static CT and compression ultrasound were calculated. Body mass index, procedure details, diagnostic yield, and complication rate were recorded. RESULTS. The biopsies of 389 patients (167 men, 222 women; mean age, 62.4 years; mean body mass index, 28.2) were assessed. Skin-to-target distance was 0-3 cm in 108 patients, 3-6 cm in 163 patients, 6-10 cm in 99 patients, and > 10 cm in 19 patients. A total of 118 deep targets were identified. The mean skin-to-target distance in the entire cohort was 5.0 cm on CT scans and 3.6 cm on ultrasound images with a 10% mean decrease in distance with ultrasound compression. For skin-to-target distances of 6-10 cm, distance decreased 39% at ultrasound, and for skin-to-target distances > 10 cm, distance decreased 48%. Thirty-three patients (8.5%) had no safe identifiable path for CT biopsy, most commonly because of intervening bowel, displacement of which at ultrasound allowed a safe biopsy trajectory. Ultrasound-guided biopsy had a diagnostic yield of 91.5% and a favorable safety profile. The complication rate was 1.3%. CONCLUSION. Application of compression with the ultrasound transducer decreased skin-to-target distance 40% or more for deep targets in addition to displacing bowel and establishing a safe path for biopsy in approximately 8.5% of cases.

Thermoacoustic range verification in the presence of acoustic heterogeneity and soundspeed errors - Robustness relative to ultrasound image of underlying anatomy

PURPOSE

To demonstrate robustness of thermooacoustic range verification to acoustic heterogeneity and discrepancies between assumed and true propagation speed, i.e., soundspeed errors.

METHODS

A beam sweeper was used to deliver 250 ns pulses that deposited 0.26 Gy of 16 MeV protons and 2.3 Gy of 60 MeV helium ions into water and oil targets, respectively. Thermoacoustic signals were detected by a 96-channel ultrasound array with a 1-4 MHz sensitivity band (-6 dB), bandpass filtered and backprojected to create thermoacoustic images in the plane of the ultrasound array. The same soundspeed and transducer array were used to estimate range and generate the ultrasound images onto which Bragg peak locations were overlaid. An air-gap phantom that displaced the Bragg peak by 6.5 mm demonstrated accuracy. Robustness to soundspeed errors was demonstrated in a waterbath as the assumed propagation speed scanner setting was altered by ± 5 % . Tissue-mimicking gelatin and a bone sample were introduced to demonstrate robustness to acoustic heterogeneity relative to ultrasound images of the underlying morphology.

RESULTS

Single ion pulse measurements sufficed during the helium run, but signal averaging was required for protons. Range and entry point into the target were estimated from data collected by transducers placed at least 6 cm distal to the Bragg peak. When ultrasound images depicted the air-target interface where the beam enters, estimates of the entry point agreed with ultrasound images and range estimates agreed with Monte Carlo simulations to within 300 μm, even when thermoacoustic emissions traveled through a strongly scattering bone sample. Estimated Bragg peak locations were translated 6.5 mm by the air-gap phantom and correctly identified scenarios when the beam stopped inside the bone.

CONCLUSIONS

Soundspeed errors dilate and acoustic heterogeneities deform ultrasound images. When thermoacoustic receivers are co-located with the ultrasound imaging array, the same transformations shift thermoacoustic range estimates. Therefore, thermoacoustic range verification is robust relative to ultrasound images of underlying anatomy. When the treatment target is visible in ultrasound, e.g., prostate, online thermoacoustic range estimates could verify that the treatment spot is inside the target.