In this PhD project two newer ultrasound techniques are for the first time used for clinical scans of
patients with malignant liver tumors (Study I), arteriovenous fistulas for hemodialysis (Study II) and
arteriosclerotic femoral arteries (Study III). The same commercial ultrasound scanner was used in all
Study I was a comparative study of B-mode ultrasound images obtained with conventional technique
and the experimental technique Synthetic Aperture Sequential Beamforming (SASB). SASB is a datareducing
version of the technique synthetic aperture, which has the potential to produce ultrasound
images of very high quality with high frame rate. Synthetic aperture is unfortunately very demanding
computationally, and is therefore used only in experimental scanners. SASB reduces the data volume
by a factor of 64, thereby making it possible to implement the technology on a commercial ultrasound
scanner, to perform wireless data transfer and in the future to develop e.g. a wireless ultrasonic
transducer. Nineteen patients with either primary liver cancer or liver metastases from colon cancer
were ultrasound scanned the day before planned liver resection. Patients were scanned simultaneously
with the conventional technique and SASB, and the image quality was subsequently evaluated from a
clinical perspective by five radiologists with ultrasound experience. The evaluations showed a slight
(statistically insignificant) advantage to SASB, and the study thereby showed that SASB, in spite of the
significant data reduction, is suitable for clinical use.
In Study II, 20 patients with arteriovenous fistulas for hemodialysis were ultrasound scanned directly
on the most superficial and accessible part of the fistula. The vector ultrasound technique Vector Flow
Imaging (VFI) was used. VFI can quantitatively estimate the direction and velocity of the blood flow in
a vessel, independently of the angle of insonation. Conventional Doppler technique is dependent on an
angle of insonation < 60-70° when a quantitative estimation of flow is needed. It is therefore
challenging to use on the very superficial arteriovenous fistulas. The fistulas were scanned
perpendicular to the vessel, the cross-sectional area was calculated and blood flow velocity measured.
The average flow velocity was calculated and multiplied by the cross sectional area, thereby calculating
volume flow in the fistula. This was compared with the gold standard for volume flow measurements
(ultrasound dilution technique), and was 31 – 35 % lower than the gold standard, but showed a
significantly improved standard deviation. The study thus demonstrated a new, direct and intuitive way
to measure blood flow in arteriovenous fistulas.
Study III was also a flow study using VFI. Eleven patients with arteriosclerotic disease in the
superficial femoral artery had an ultrasound scan of the vessel performed just before a planned
angiography of the arteries. If turbulent/disturbed flow was identified with VFI, and suspicion of a flow
disturbing arteriosclerotic lesion was raised, recordings of the flow were made. The recordings were
subsequently analyzed, and for each recording blood flow velocity at the lesion was compared with the
flow velocity in a healthy adjacent arterial segment. If the velocity at the lesion was higher than in the
healthy segment, it was considered a stenosis. By comparison with the subsequent angiography a strong
correlation was found between the calculated velocity ratios and the measured angiographic stenosis
degrees. Thus, it was possible to assess stenosis degree quantitatively from the VFI ultrasound scan.
Furthermore, it was calculated that a doubling of the flow velocity indicates a stenosis degree of 50 %,
and thus a clinically significant stenosis requiring treatment. The study is the first of its kind where a
vector ultrasound technique is used to calculate velocity ratios related to arteriosclerotic stenoses, and
the obtained results are consistent with previous studies performed with conventional Doppler
technique. Use of VFI is more intuitive, and may be used to perform faster and more accurate screening
of these patients before they are referred to angiography.
The three studies demonstrate the first application of the new ultrasound techniques in selected groups
of patients. For all three studies the results are promising, and hopefully the techniques will find their
way into everyday clinical practice for the benefit of both patients and healthcare practitioners.
PhD by Peter Møller Hansen in collaboration with Rigshospitalet. Submitted October, 2014