Quo vadis medical ultrasound?

[Current state of under- and postgraduate education in abdominal ultrasonography at German university hospitals. A panel study over 20 years]

OBJECTIVE

 In Germany, there is no standardized ultrasound training. This study aims to provide a survey into the current state of abdominal ultrasonography training at German university hospitals as well as a comparative analysis of the results from studies conducted in 1999 and 2009.

METHODS

 Chief gastroenterologists from Germany's 34 university hospitals were invited to respond to a postal survey asking about technical equipment, the number of ultrasound scans, the role of professional societies and undergraduate as well as postgraduate training. The response rate was 79 %. In addition, 1183 medical students from 34 faculties completed a complementary online teaching evaluation.

RESULTS

 At university hospitals, abdominal ultrasonography is conducted in an increasingly interdisciplinary context. Today, 29 % of university hospitals have interdisciplinary ultrasound centers. The study shows that the number of available ultrasound machines has increased - each hospital has an average of 5.2 systems. This is an increase of 30 % in comparison to 2009 and of 27 % in comparison to 1999. However, the willingness to invest in modern ultrasound machines has decreased. The total number of ultrasound scans as well as the number of contrast-enhanced ultrasound scans have steadily increased over the past years - with a maximum increase of 28 % between 2009 and 2018. The German Society of Ultrasound in Medicine (DEGUM) is increasingly present at university hospitals. It has further strengthened its prominent role in quality assurance and specialist training. Today, 96 % of the chief gastroenterologists are members of DEGUM and 89 % have obtained further qualification offered by the society. Concerning the duration of the training, the number of mandatory examinations and the amount of supervision, there are still considerable differences among the departments. On average, more doctors are trained per department and year. A 6-month full-time training has been established at most hospitals. Sonography enjoys a high standing among students and the findings show a strong readiness for work in that field. The number of practical courses and students has been increasing over the past years. However, there is often an imbalance between the number of courses offered and students who want to enroll.

CONCLUSIONS

 Training conditions have improved for medical staff as well as students despite the fact that there are still considerable differences in quality among the hospitals. The number of ultrasound scans is steadily increasing in all departments. The study did not show any adequate improvement in the availability of technical equipment. The German Society of Ultrasound in Medicine (DEGUM) has further strengthened its leading position in the field of sonography.

Harmonic motion imaging for abdominal tumor detection and high-intensity focused ultrasound ablation monitoring: an in vivo feasibility study in a transgenic mouse model of pancreatic cancer

Harmonic motion imaging (HMI) is a radiationforce- based elasticity imaging technique that tracks oscillatory tissue displacements induced by sinusoidal ultrasonic radiation force to assess the resulting oscillatory displacement denoting the underlying tissue stiffness. The objective of this study was to evaluate the feasibility of HMI in pancreatic tumor detection and high-intensity focused ultrasound (HIFU) treatment monitoring. The HMI system consisted of a focused ultrasound transducer, which generated sinusoidal radiation force to induce oscillatory tissue motion at 50 Hz, and a diagnostic ultrasound transducer, which detected the axial tissue displacements based on acquired radio-frequency signals using a 1-D cross-correlation algorithm. For pancreatic tumor detection, HMI images were generated for pancreatic tumors in transgenic mice and normal pancreases in wild-type mice. The obtained HMI images showed a high contrast between normal and malignant pancreases with an average peak-to-peak HMI displacement ratio of 3.2. Histological analysis showed that no tissue damage was associated with HMI when it was used for the sole purpose of elasticity imaging. For pancreatic tumor ablation monitoring, the focused ultrasound transducer was operated at a higher acoustic power and longer pulse length than that used in tumor detection to simultaneously induce HIFU thermal ablation and oscillatory tissue displacements, allowing HMI monitoring without interrupting tumor ablation. HMI monitoring of HIFU ablation found significant decreases in the peak-to-peak HMI displacements before and after HIFU ablation with a reduction rate ranging from 15.8% to 57.0%. The formation of thermal lesions after HIFU exposure was confirmed by histological analysis. This study demonstrated the feasibility of HMI in abdominal tumor detection and HIFU ablation monitoring.

Assessment of liver size by ultrasonography

BACKGROUND

To determine liver span sonographically in a randomly selected population sample and identify factors that affect liver size.

METHODS

A total of 1,789 subjects (963 females, 826 males; mean age 41.8 ± 12.8 years) underwent sonographic examination of the liver in the midclavicular line to determine liver span. Subjects underwent physical examination and blood tests and completed a standardized interview questionnaire.

RESULTS

The average liver span in the midclavicular line for the overall collective was 15.0 ± 1.5 cm; the average for females was 14.9 ± 1.6 cm and 15.1 ± 1.5 cm for males. Liver span exceeded 16 cm in 24.3% of subjects. Results of the multivariate analysis showed that, of the factors potentially influencing liver span, gender, age, body mass index, body height, fatty liver (p < 0.0001), waist-to-hip ratio (p = 0.015), and metabolic syndrome (p = 0.032) are significant. By contrast, diabetes mellitus, alcohol consumption, tobacco consumption, physical activity, and laboratory findings showed no influence.

CONCLUSIONS

Sonographic measurement of liver span in the midclavicular line is a simple method for routine clinical use. Gender, age, body mass index, waist-to-hip ratio, body height, hepatic steatosis, and metabolic syndrome are factors associated with liver span.

Structural and permeability sensitivity of cells to low intensity ultrasound: Infrared and fluorescence evidence in vitro

This work is focused on the in vitro study of the effects induced by medical ultrasound (US) in murine fibroblast cells (NIH-3T3) at a low-intensity of exposure (spatial peak temporal average intensity Ita<0.1Wcm(-2)). Conventional 1MHz and 3MHz US devices of therapeutic relevance were employed with varying intensity and exposure time parameters. In this framework, upon cells exposure to US, structural changes at the molecular level were evaluated by infrared spectroscopy; alterations in plasma membrane permeability were monitored in terms of uptake efficiency of small cell-impermeable model drug molecules, as measured by fluorescence microscopy and flow cytometry. The results were related to the cell viability and combined with the statistical PCA analysis, confirming that NIH-3T3 cells are sensitive to therapeutic US, mainly at 1MHz, with time-dependent increases in both efficiency of uptake, recovery of wild-type membrane permeability, and the size of molecules entering 3T3. On the contrary, the exposures from US equipment at 3MHz show uptakes comparable with untreated samples.

Real-time ultrasound attenuation imaging of diffuse fatty liver disease

A method for real-time ultrasound attenuation imaging and quantification is proposed in this paper. We employed a simple algorithm for comparing two signal intensities of different frequencies to extract attenuation quantitatively. The usefulness of this method was verified by numerical simulation of the acoustic field and validated by phantom experiments. The accuracy of the results was reduced by noise in areas with a low signal-to-noise ratio, but we found that the effects of noise could be reduced by applying our noise cancellation technique or simply setting a sufficiently high gain. The estimated attenuation coefficients for clinical liver images showed acceptable correlation with the liver-to-spleen ratio of computed tomography numbers. These findings suggest that real-time attenuation parametric imaging may be able to replace CT for quantifying the degree of fatty infiltration of the liver. However, further development is needed to obtain the local attenuation distribution in cross sections with sufficient reliability.

Processing of subharmonic signals from ultrasound contrast agents to determine ambient pressures

Subharmonic-aided pressure estimation (SHAPE) is a technique that utilizes the subharmonic emissions, occurring at half the insonation frequency, from ultrasound contrast agents to estimate ambient pressures. The purpose of this work was to compare the performance of different processing techniques for the raw radiofrequency (rf) data acquired for SHAPE. A closed loop flow system was implemented circulating reconstituted Sonazoid (GE Healthcare, Oslo, Norway; 0.2 ml for 750 ml diluent) and the beam-formed unprocessed rf data were obtained from a 4 mm diameter lumen of a Doppler flow phantom (ATS Laboratories, Inc., Bridgeport, CT) using a SonixRP scanner (Ultrasonix, Richmond, BC, Canada). The transmit frequency and incident acoustic pressures were set to 2.5 MHz and 0.22 MPa, respectively, in order to elicit Sonazoid subharmonic emissions that are ambient-pressure sensitive. The time-varying ambient pressures within the flow phantom were recorded by a Millar pressure catheter. Four techniques for extracting the subharmonic amplitude from the rf data were tested along with two noise filtering techniques to process this data. Five filter orders were tested for the noise removing filters. The performance was evaluated based on the least root-mean-square errors reported after linear least-square regression analyses of the subharmonic data and the pressure catheter data and compared using a repeated ANOVA. When the subharmonic amplitudes were extracted as the mean value within a 0.2 MHz bandwidth about 1.25 MHz and when the resulting temporally-varying subharmonic signal was median filtered with an order of 500, the filtered subharmonic signal significantly predicted the ambient pressures (r2 = 0.90; p < 0.001) with the least error. The resulting root mean square and mean absolute errors were 8.16 +/- 0.26 mmHg and 6.70 +/- 0.17 mmHg, respectively. Thus, median processing the subharmonic data extracted as the mean value within a 0.2 MHz bandwidth about the theoretical subharmonic frequency turned out to be the best technique to process acoustic data for SHAPE. The implementation of this technique on ultrasound scanners may permit real-time SHAPE applications.

Simultaneous grayscale and subharmonic ultrasound imaging on a modified commercial scanner

OBJECTIVE

To demonstrate the feasibility of simultaneous dual fundamental grayscale and subharmonic imaging on a modified commercial scanner.

MOTIVATION

The ability to generate signals at half the insonation frequency is exclusive to ultrasound contrast agents (UCA). Thus, subharmonic imaging (SHI; transmitting at f(0) and receiving at f(0)/2) provides improved visualization of UCA within the vasculature via suppression of the surrounding tissue echoes. While this capability has proven useful in a variety of clinical applications, the SHI suppression of surrounding tissue landmarks (which are needed for sonographic navigation) also limits it use as a primary imaging modality. In this paper we present results using a commercial ultrasound scanner modified to allow imaging in both grayscale (f(0)=4.0 MHz) and SHI (f(0)=2.5 MHz, f(0)/2=1.25 MHz) modes in real time.

METHODS

A Logiq 9 ultrasound scanner (GE Healthcare, Milwaukee, WI) with a 4C curvilinear probe was modified to provide this capability. Four commercially available UCA (Definity, Lantheus Medical Imaging, North Billerica, MA; Optison, GE Healthcare, Princeton, NJ; SonoVue, Bracco Imaging, Milan, Italy; and Sonazoid, GE Healthcare, Oslo, Norway) were all investigated in vitro over an acoustic output range of 3.34 MPa. In vivo the subharmonic response of Sonazoid was investigated in the portal veins of four canines (open abdominal cavity) and four patients with suspected portal hypertension.

RESULTS

In vitro, the four UCA showed an average maximum subharmonic amplitude of 44.1±5.4 dB above the noise floor with a maximum subharmonic amplitude of 48.6±1.6 dB provided by Sonazoid. The average in vivo maximum signal above the noise floor from Sonazoid was 20.8±2.3 dB in canines and 33.9±5.2 dB in humans. Subharmonic amplitude as a function of acoustic output in both groups matched the S-curve behavior of the agent observed in vitro. The dual grayscale imaging provided easier sonographic navigation, while the degree of tissue suppression in SHI mode varied greatly on a case by case basis.

CONCLUSIONS

These results demonstrate the feasibility of dual grayscale and SHI on a modified commercial scanner. The ability to simultaneously visualize both imaging modes in real time should improve the applicability of SHI as a future primary clinical imaging modality.

A stochastic model for propagation through tissue

Attenuation of ultrasonic waves is often assumed linear with respect to frequency in biological applications whereas it is considered quadratic when the propagation occurs in the atmosphere or the water. In the latter case, other studies show that a Gaussian propagation duration can explain this attenuation behavior and provide a model for the energy loss in the stationary limit. The present paper defines an equivalent random propagation duration with Cauchy distribution, which is appropriate for the propagation of ultrasound through tissue. The model adds an unobserved noise that represents the signal deterioration. In addition, the model agrees with the mode downshift in the case of a narrowband signal.

Flexible ultrasonic transducers incorporating piezoelectric fibres

It is possible to produce a high-performance, flexible 1-3 connectivity piezoelectric ceramic composite with conventional methods but the process is difficult and time-consuming. Extensive finite element modeling was used to design a piezocomposite structure which incorporated randomly positioned piezoceramic fibers in a polymer matrix. Simple manufacturing techniques were developed which resulted in the production of large numbers of fully populated fiber composites that offered performance comparable with a conventional 1-3 piezocomposite. A modified process facilitated the production of efficient fiber piezocomposite elements separated by polymer channels which conformed to a highly flexible (13 mm radius of curvature), 2-D matrix array configuration. This arrangement has been termed a Composite Element Composite Array Transducer, or CECAT. These devices were evaluated in terms of their impedance spectra, pulse-echo response, and surface displacement characteristics. The random piezoceramic fiber arrangements showed comparable sensitivity and bandwidth to periodic devices while minimizing the parasitic interpillar modes associated with periodic structures. Investigations have indicated that CECAT arrays constructed with 250 microm diameter fibers can be operated at frequencies of up to 3 MHz and transducers incorporating 10 microm diameter fibers can extend the frequency range above 6 MHz. Conversely, improved low-frequency devices can be produced with taller pillars than possible with conventional manufacturing techniques.

Trends and future needs in clinical radiology: insights from an academic medical center

OBJECTIVE

Advances in technology, expanding indications and defensive medical practice, in combination with population aging, have all contributed to a substantial increase in utilization of imaging and therapeutic radiology procedures in recent years. Moreover, the integration of education, innovation and research into high-volume workflow, although challenging, is a key requirement in teaching hospitals. Therefore, identifying forthcoming demand in the use of radiology services at a referral center might be of special interest and facilitate health policy planning in this context.

METHODS

Data regarding conventional radiographic, ultrasonographic and computed tomography (CT) investigations, radiotherapy sessions, and interventional procedures were collected for a 5-year period (2000-2004). Based on these observations, we deployed appropriate models to forecast utilization rates in 2005-2009.

RESULTS

Between 2000 and 2004, ultrasound examinations increased by 31.8%, mammography by 31.6%, CT scans by 17.4%, interventions by 14.5% and radiotherapy sessions by 13.9%, while conventional investigations decreased by 42.5%. We identified significant increasing trends for ultrasound, mammography, CT and interventions (all p<0.001 for linear component). Compared to current levels, the workload for these modalities is expected to rise in the next 5 years by 43%, 31%, 20% and 14%, respectively. Radiotherapy sessions demonstrate an unstable, non-significant increasing trend (p=0.189), while utilization of conventional radiography declines rapidly (p<0.001 for linear trend, 5-year prediction -51%).

CONCLUSIONS

In forthcoming years, the demand for radiology services at referral centers will increase substantially. Advances in digital technology alone will not suffice to completely alleviate the need for additional resources and well-trained personnel.