Two devices in one – that is one of the mega trends in
imaging diagnostics. The spectrum ranges from a combination of positron
emission tomography (PET) with MRI or computer tomography to a combination of
ultrasound with endoscopy. At MEDICA 2010, World Forum for Medicine –
International Trade Fair and Congress, to be held from November 17 – 20, 2010
in Düsseldorf, Germany, medical technology
companies and congress speakers will focus on innovative hybrid procedures such
as endosonography and its application in the daily clinical routine. Use of
these so-called hybrid procedures is increasing, primarily on cancer patients.
The idea is obvious: Combine two diagnostic procedures in a
single examination in order to obtain the information from two procedures, not
just from one imaging method, more easily and with less stress for the patient.
This is made possible by these hybrid procedures, in which two different
imaging methods are combined in a single comprehensive technical system.
One example of a special hybrid system is the whole-body PET
/ MRT scanner, equipped with the latest Philips technology, which was installed
at the University Hospital of Geneva this year. However, it will still be used
primarily for research purposes. This system combines two procedures which were
not combinable up to now, namely magnetic resonance tomography (MRT) and
positron emission tomography (PET). The combination of MRT and PET allows the
spatial structures and the metabolism activity of the organs to be displayed in
a single image. This is of particular interest in cancer treatment, because
tumor cells often require more energy than the healthy cells in adjacent
tissue. This is important for initial diagnosis, surgery planning and verifying
how successfully the tumor was treated.
“The combination of anatomical imaging by MRT and the
metabolism through the applied, radioactively marked tracer for PET will assist
in monitoring and prediction as well as supervising the treatment of cancer
patients and will provide more precise information on how the patients respond
to treatments. We also believe that hybrid imaging will also have more potential
in other areas, particularly in cardiovascular imaging as well as neurology,”
explains Professor Osman Ratib, Chief Physician at the Clinic of Radiology and
Nuclear Medicine of the University
of Geneva.
Currently, both MRT and PET examinations are performed
separately, often over several days. Then the images are superimposed on the
processing console. Consequently it is very difficult to match the images
precisely, as the patient is never in exactly the same position during the examinations
and the alignment of the respective scanners does not always correspond
precisely. Large diagnostic devices that combine PET and computer tomography
have been in use for years as PET/CT devices. In contrast, the combination MRT
and PET was thought to be virtually unfeasible. “Up to now, the magnetic field
of the MRT prevented the proper functioning of the PET scanner and created
artefacts,” says Professor Ratib. These problems have been solved in the new
whole-body PET / MRT scanner. With the hybrid device, the two scanners are
located in a room opposite to each other. In between is a rotating table, so
that PET and MRT can take place one after the other without the patient
changing position. “We chose three particular areas in which we expect a
significant improvement,” states Professor Ratib. These are, firstly, patients
with head/neck tumors where the evaluation of tumor recidivation with
conventional imaging is often very difficult due to the frequently very radical
surgery. The PET / MRT will also be used for prostate cancer, where the primary
aim is the early recognition of recidivation, and for breast cancer, where the
procedure will help to improve the differential diagnostics.
Significantly less examination stress
Radiologists at the University Hospital of Tübingen have had
a combined PET MRT system for a year already. Professor Claus D. Claussen,
Medical Director at the Department of Radiology, remarks: “For our patients,
this means that in future there will be significantly less examination stress
because the examination time can be considerably reduced and the exposure to
radiation will be eliminated. This technology allows earlier recognition of
tumors and metastases, they can be characterized more clearly, and their
location relative to the organs more definitely established. The expected
result will be earlier and more targeted therapy.” The University Hospital
has already completed important steps in the development of PET-MRT for the
head. Now the challenge for scientists is to adapt the imaging technology for
the head, which is relatively small, to the whole body. The PET-MR for brain
imaging was developed in cooperation with Siemens.
Researchers in Jülich expect to recognize brain diseases
such as Alzheimer’s in the very early stages with a PET plus a strong MRT of
9.4 tesla (that is almost 200,000 times stronger than the earth’s magnetic
field) – a technology also developed by Siemens. The device simultaneously
records the tissue structure and biochemical processes in the brain. The
director of the Institute for Neurosciences and Medicine, Professor Jon Shah,
expects a resolution of under 0.1 millimetres. Researchers also expect advances
in basic research, for instance with respect to addiction and headache.
However, improved diagnosis does not mean immediate improved therapy. It may
take years until new therapeutic agents developed on the basis of this research
can be tested.
Combination of MR and ultrasound
With MRgFUS and MR-Touch, the US company GE Healthcare has two
hybrid procedures in its range of products. MRgFUS is a combination of MRT and
highly focused ultrasound for myoma therapy. MR-Touch is a special elastography
procedure that allows visual scanning of organs. For centuries, physicians have
relied on their sense of touch when examining their patients, for instance when
feeling for lumps in the breast or palpating the liver in order to recognize
liver fibrosis. However, not all the organs can be reached like that. MR-Touch
provides the solution. The process utilizes a combination of low-frequency
sound waves and MR technology to measure the elasticity of the tissue. This
produces an elastogram, a color-coded anatomical image of the firmness of the
liver tissue. The process comprises three steps. First, sound waves (between 40
and 200 Hz) are generated in the body by means of an MRT-compatible generator.
In the second step, an image of these sound waves is created with a special MR
imaging sequence. In the third and last step, these data are processed and an
elastogram is created which shows the relative firmness of the tissue in the
area being examined.
The advantage of endosonography (EUS, endoscopic ultrasound)
is also the combination of two imaging procedures, in which the organs are not
examined from the outside through the skin, but from the inside. The ultrasound
head directly contacts interior surfaces such as the mucosa of the oesophagus
by means of an endoscope. In contrast to conventional ultrasound examinations
through the skin, the advantage of this procedure is that the target organ is
closer to the ultrasound head, therefore allowing it to be displayed more
precisely or actually displayed at all. A balloon filled with water is often
placed on the tip of the endoscope in order to enhance the display. This
improves conduction of the ultrasound waves to the tissue as well as improved
reflection. Different devices are used, for instance those made by Olympus,
depending of the area of application. Miniprobe systems are related to
endosonography. These are instruments that can be pushed through a biopsy
channel, for instance. However, the radius of the penetration depth of the
ultrasound is smaller. Miniprobe endosonography is particularly suitable for
such procedures as the targeted examination of a polyp or to estimate the depth
of a malignant tumor.
Endosonography gains in significance
Endosonography “allows the observation of almost
microscopically precise sectional images of the intestine wall,” explains Dr.
Elke Burmester of Sana Clinics in Lübeck. The examination itself is relatively
simple and not very stressful for patients. The significance of endosonography
in imaging diagnostics, above all for colorectal diseases, has increased in
recent years and it is now considered an important diagnostic building block.
On the one hand this applies for assessment of the continence organ, anorectal
abscesses and fistulas. On the other hand, with respect to cases of rectal
carcinoma endosonography is now an obligatory component of the current
S3-guidelines (S3 = highest guideline classification issued by Germany’s
Association of Scientific Medical Societies AWMF). Determination of the tumor
infiltration depth and evidence of lymph node metastases is very precise. The
hybrid procedure allows exact therapy control with tumor follow-up, through
which it is possible to recognize and precisely puncture suspicious findings.
This procedure is also an option in the diagnosis of tumors
in the area of the pancreas and in cases of unclear cholistasis. According to
Burmester, the results of EUS in pancreatic procedures are rather
unsatisfactory. In addition, endosonography is particularly sensitive in the
diagnosis of neuroendocrine tumors of the pancreas. It is even indispensable for
the diagnosis of insulinoma for pre-operative planning.
For additional information on the products and
technologies discussed in this article, see MEDICA 2010.
