Despite constant improvements within the field of medical ultrasound, there are still a considerable number of difficult-to-image patient. Echocardiograms (heart images) taken from these patients do not have the quality that is needed for correct diagnosis. Therefore it is important to further improve the quality of echocardiograms.

Understanding the reasons behind low-quality images is essential to find methods to improve the quality. At the Centre for Innovative Ultrasound Solutions (CIUS), we have performed a systematic study to understand the mechanisms causing the problems in difficult-to-image patients.

In my previous blog post, we showed that the tip of a needle placed out of the imaging plane (the cross section of the object that is imaged), is seen in the ultrasound image if some part of the ultrasound signal hits the bones and gets deflected towards the needle. The question was then if there are some types of tissue in the body that can play the role of the needle and make noise by sending the deflected signal back to the ultrasound transducer.

We have now attempted to answer this question by performing different water tank experiments where we imaged an artificial heart chamber in the presence of two pieces of rib bones. In these experiments, we placed the bones at different angles relative to the ultrasound transducer and used different types of tissue such as skin, fat and lung to study the effect of these on the images.

Figure 1- Beamprofile measurement of an ultrasound transducer. a) without ribs, b) with ribs partly blocking the transducer, and c) with ribs at a different angle from b).

The results of these experiments show that depending on the angle between the ultrasound beam and the ribs, the ultrasound signal can be partly reflected either outside or inside the ribcage (see Figure 1). The measured energy from the transducer can be seen as a single beam in Figure 1a. In Figure 1b and 1c, the ultrasound signal is split in two parts after hitting the rib. Different angles between the transducer and the ribs in these two measurements results in reflection of signal outside the ribcage (above the bones) in 1b and inside the ribcage (below the bones) in 1c. Therefore, we can consider two cases:

Case 1: the reflection of signal is outside the patient’s chest.

Figure 2- Watertank experiment with rib bones and a layer of fat. State 1) large distance between the ribs, state 2) reduced distance between the ribs, and state 3) the fat layer is removed.

This reflected signal can then hit the subcutaneous fat and travel back to the transducer. The received echoes from subcutaneous fat are then shown as noise over the image of the heart. We experimentally demonstrated this case by the setup shown in Figure 2. In this experiment, the bones were placed in a way that the reflection of the signal was outside the ribcage (same as in Figure 1b). The upper row shows three instances of this experiment, while the lower row shows the corresponding ultrasound images taken by the transducer. A layer of fat was placed over the ribs to simulate the effect of the subcutaneous fat inside the body. A clear ultrasound image of the heart chamber can be seen in State 1 where there is a big enough distance between the bones and therefore no reflection of signal towards the fat layer. In State 2, however, where the distance between the bones is reduced, the ultrasound image of the heart chamber is covered with a haze-like noise. Finally, in State 3, the fat layer is removed while keeping the distance between the ribs as short as in State 2. The haze-like noise is mostly removed from the ultrasound image in this state.

Case 2: the reflection of signal is inside the patient’s chest.

Figure 3- Watertank experiment with rib bones and a piece of sponge. State 1) large distance between the ribs, state 2) reduced distance between the ribs, and state 3) the sponge is removed.

In this case, the lung tissue can send the signal back to the transducer and cause the degradation of the image quality. This case was experimentally demonstrated by the setup shown in Figure 3. In this experiment, the bones were placed at a slightly different angle from the first experiment so that the reflection of the signal was inside the ribcage (same as in Figure 1c). The same steps were followed as in the first experiment, but instead of the fat layer over the ribs a piece of sponge was placed under the ribs and close to the heart chamber. The sponge simulates the effect of the lungs in the body because of the air trapped inside it. Similar ultrasound images as in previous experiment can be seen here.

The results of these experiments confirm that the deflection of ultrasound signal by the ribs in unwanted directions followed by a second reflection from either fat layers or lung tissue can generate noise in echocardiograms. This knowledge can be applied to implement new techniques in order to improve the quality of echocardiograms in difficult-to-image patients.

A collaboration between several institutions, including the Norwegian University of Science and Technology (NTNU), the University of Michigan Medical School, Geisinger and Regeneron, and deCODE Genetics/Amgen in Iceland, has resulted in surprising results linking atrial fibrillation in adults to fetal heart development. 

The group studied an unprecedented sample size of over one million people, including over 60,000 individuals with atrial fibrillation, to discover over 140 genetic changes associated with this common, adult-onset cardiac arrhythmia. The results were surprising in that they identified a number of genes that control heart development in the fetus.

This could have important implications for future treatment and possibly prevention of atrial fibrillation.

Experiments in rabbits with induced heart failure showed that at least one of the fetal genes becomes active again in the damaged heart. Because the fetal genes have different rates of conduction of the cardiac electrical impulses relative to the adult form of the gene, atrial fibrillation is induced. This could have important implications for future treatment and possibly prevention of atrial fibrillation.

The group are hopeful that additional molecular biology experiments will determine how to create sustained regular heart rhythms by studying the genes they, and others, have identified.

Significance of the expression enrichment for the atrial fibrillation candidate genes.

They also found that for each individual, they could count the number of genetic changes that each person carries to predict which people are most at risk for developing atrial fibrillation in the future. This may have important implications for precision health and prevention of cardiovascular disease.

Another paper on atrial fibrillation was also published recently in Nature Genetics and we look forward to bringing these two collaborative groups together to generate an even larger study for the benefit of those afflicted by atrial fibrillation.

Read the full article in Nature Genetics. 

Using an application developed at NTNU, helps physicians detect more patients with reduced heart function when assessing heart pump function in patients with suspected heart failure using ultrasound.

Heart failure is a common disease among the elderly. Increased use of ultrasound of the heart or echocardiography, in primary health care can result in faster diagnostics and treatment. A hurdle is that echocardiography is a challenging methodology, especially for inexperienced users. A possible solution could be automatic measurements that tells the examiner if the imaged heart pumps well or not.

At NTNU, we have developed an application that measures movement patterns of the heart automatically. We tested the method on more than 200 patients, who were examined by experienced cardiologists, evaluating the true pumping function.

The author presenting the results at the European Society of Cardiology Congress poster session in Barcelona.

The application was run on images taken by the cardiologists and we investigated if the automatic measurements could be used to detect reduced heart function, and how the method performed compared to the experienced cardiologists.

The results were promising, as the automatic classification was correct in about 80% of the patients.

The results will be published in the respected journal Ultrasound in Medicine and Biology. An oral presentation of the work at the Norwegian Society of Cardiology was awarded the best scientific presentation.

Blogger: Ali Fatemi, PhD Candidate
Centre for Innovative Ultrasound Solutions (CIUS), Department of circulation and medical imaging

Cardiovascular diseases (CVDs) are the number-one cause of death globally. An estimated 17.5 million people died from CVDs in 2012, 31% of all global deaths. One important factor in preventing cardiovascular disease, is early diagnosis using technologies such as ultrasound echocardiography. In this project, we study the cause of certain defects in the current echocardiograms and will try to propose new processing methods to improve the image qualities.

The quality of cardiac ultrasound images (echocardiograms) has increased significantly in the last 20 years, making it possible to correctly diagnose the occurrence of CVDs in about 80% of patients. In the remaining 20% certain physical factors hinder a correct visualization of the heart and the assessment of its function.

One of the artefacts which is seen in the echocardiograms taken from some patients, is what we refer to as “haze” artefact. In the images with this artefact a haze-like noise can be seen over the heart. This haze-like noise normally disappears when imaging deeper than 10 cm into the body in the studied cases (see the hazy echocardiogram in the figure below). In the following figure a “non-hazy” echocardiogram is shown together with a “hazy” one.

Left: a ”clear” ultrasound image of heart. Right: a ”hazy” ultrasound image of heart

Echocardiography produces real-time images of the heart, by sending ultrasonic pulses (sound waves with higher frequency than audible frequency range) in between the ribs and down into the body. Ultrasonic pulses are then reflected back to the transducer (the transmitter and receiver of the ultrasonic pulses), which can be detected and transformed into an image. However that is not the only path that the signal can take. Sometimes the signal can be partially blocked by the ribs impacting the quality of the result images. Therefore, as a potential cause of the haze artefact, we investigate the geometry of rib bones and its effect on the received ultrasound signal from the heart.

To study this effect, we carried out an experiment out of the body, where we imaged an artificial ventricle in a water tank. A section of a pork ribcage was placed on top of it to simulate the ribs effect in human body (see figure below). We imaged the ventricle through the ribs with an M5Sc transducer and E95 GE scanner. We repeated the imaging after placing the tip of a metal needle under water about 10 cm away from the transducer. Figure below shows the setup with and without the needle and the corresponding ultrasound images. We observe that the needle tip is displayed in the ultrasound image at a depth of around 11 cm (see the lower right pane in the figure below). However the needle is not expected to be visible in the image since it is placed out of the transducer field of view or “imaging plane” (a cross section of the object which is being imaged).

Images of the setup and corresponding ultrasound images with and without the needle. Upper left pane: image of the setup without the needle. Lower left pane: ultrasound image without the needle. Upper right pane: image of the setup with the needle. Lower right pane: ultrasound image with the needle.

This experiment shows that if the ultrasound beam is partially blocked by the ribs, then part of the energy is reflected to unwanted directions. This deflected energy can then be reflected once more by the scatterers that are present in these directions (the needle tip in our experiment) and travels back to the transducer. Therefore, the scatterers out of the imaging plane can be observed in the ultrasound image as noise. The result of this experiment can be expanded to the haze artefact in the echocardiograms with the hypothesis being:

In some patients, with a specific shape and angle of the ribs, and depending on the heart position relative to the ribs, there is no way for all of the ultrasound beam to go through the ribs before hitting the desired cross section of the heart. This leads to the beam being partially reflected and any scattering tissue out of the imaging plane is then rendered as haze noise.

At this stage, we are collecting some live data from volunteers to check the haze level in their echocardiograms. At the same time, we record some data of the shape and distance of their ribs and compare the haze level with this information.

“Our models may be used to identify high-risk patients in order to provide a basis for a meaningful informed consent; for making decisions on whether or not to recommend surgery; and to weight between risk and benefit for an individual patient,” says PhD candidate Yunita Widyastuti at the Department of Laboratory Medicine, Children’s and Women’s Health (LBK) at NTNU.

The three models for predicting heart problems (cardiac dysfunction), prolonged need for respirator treatment (mechanical ventilation) and length of intensive care unit (ICU) stay, are said to be more accurate for Norwegian patients than previous models. This is because they were developed using patient data from approximately 5000 heart patients operated at St. Olavs Hospital in Trondheim over the period 2000-2007.

The ICU model, although fairly accurate, is less useful however, as the length of stay in intensive care tends to depend on hospital policy.

All three models are based on similar heart-related variables as previous models, but the variables are weighted differently making them more accurate for Norwegian patients, Widyastuti explains.

Viva

Yunita Widyastuti will defend her thesis “Risk factors for common complications following adult heart surgery” at 12.15 on 13. December, 2012, in the MTFS Auditorium at NTNU.

A trial lecture titled “The impact of blood product transfusion on mortality and morbidity after cardiac surgery” will be held in the same place at 10.15 am.

Related publications

• Length of intensive care unit stay following cardiac surgery: is it impossible to find a universal prediction model? Widyastuti Y, et.al.
• Preoperative and intraoperative prediction of risk of cardiac dysfunction following open heart surgery. Widyastuti Y et.al.
• Pre-operative and intraoperative determinants for prolonged ventilation following adult cardiac surgery. Widyastuti Y, et.al.

 Certain inflammation markers seem to be related to increased risk of ischemic heart disease (angina pectoris and heart attack), according to three studies conducted by Cand.med. Inga Thorsen Vengen at the Department of Laboratory Medicine, Children’s and Women’s Health, NTNU.

Publications

• Mannose-binding lectin deficiency is associated with myocardial infarction: the HUNT2 Study in Norway. Vengen IT et.al. (Submitted)
• Lactoferrin is a novel predictor of fatal ischemic heart disease in diabetes mellitus type 2: Long-term follow-up of the HUNT 1 study. Vengen IT et.al. Atherosclerosis 2010.
• Neopterin predicts the risk for fatal ischemic heart disease in type 2 diabetes mellitus. Long-term follow-up of the HUNT 1 study. Vengen IT et. al. Atherosclerosis 2009.