Modern X-ray Imaging – The Workhorse in Radiology
Fig.1: Evaluation of a CT scan
It was Conrad Roentgen who laid the foundation for looking inside the human body in 1895 when he made the then sensational discovery of ‘X-rays’. Honoring the achievements of the Nobel Prize laureate, in many countries X-rays are referred to as ‘Roentgen rays’.
Today, the X-ray technique is a frequently used imaging procedure in medicine, at present second only to ultrasound. It measures the density of tissues by absorption of X-rays and allows for marvelous images of dense tissues like bones. However, the differentiation of soft tissues is much less clear. Contrast media are necessary to create an artificial contrast between the organ to be diagnosed and vascular or surrounding anatomic structures. The detection of pathological changes in soft tissues also requires optimal contrast enhancement.
There are many radiological examinations in practice today that involve the use of contrast media. A few of the most common are described here.
Computed tomography – a constantly developing success story
In radiology, computed tomography (CT) is considered to be among the most important innovations since the discovery of X-rays. Only a few years after its invention in the early seventies, in 1979 Godfrey N. Hounsfield and A.M. Cormack were awarded the Nobel Prize in medicine for their groundbreaking work.
Based on X-rays, computed tomography initially produces a series of cross-sectional images of the investigated organ which are then processed by a special software, resulting in a volume data set. This data set allows for reconstructing two- and three-dimensional images in different planes.
Today, computed tomography represents an established high-quality technology which has advanced to become an indispensable and integral component of routine medical diagnostics. It allows detailed insight into the body and provides physicians with a solid basis for therapy decisions for the benefit of their patients. CT is applied in diagnostic examinations from tip to toe. Fields of special importance are acute care, the diagnoses of heart diseases, examinations of the head and oncology indications.
Important developments in computed tomography
Since the invention of computed tomography in 1972 the technology has undergone a dynamic development resulting in a series of innovations. Over the years Bayer HealthCare Pharmaceuticals has always been in a leading position for adapting contrast media application protocols with each new scanner generation.
Sequential CT
In the original sequential CT, X-ray tube and detector are rotating around the patient who does not change his position. In case he moves during the scan artifacts are the result that make a clear diagnosis difficult. Sequential CT is therefore of limited use for scans of organs with motion or high through flow such as the heart, lung or vascular structures.
Spiral or helical CT
In the end of the eighties first spiral scanners came to the market. In spiral CT the patient is smoothly moved through the scanner at a constant speed while X-ray source and detector – the gantry – is rotating spirally around the patient. Spiral CT allows shorter examination times and reduces movement artifacts. In addition, spiral CT provides a powerful tool to reconstruct 3D images of the investigated anatomy.
The introduction of multi-slice or multi-row CT has increased the efficiency of this technique multiple times. The number of detector rows has been continuously raised. By simultaneously scanning several slices the scan time can be reduced significantly. Today, 64 slice CT scanners are state of the art but the development is still proceeding: 256 and 320 slice CTs are already under clinical evaluation.
Dual Source CT
The latest evolutionary leap in the dynamic development of computed tomography is represented by Dual Source CT which has become commercially available since 2005. With its two x-ray tubes DSCT scanners work twice as quickly as conventional high-resolution scanners. Because of their incredible speed – a whole scan takes less than 10 seconds – sharp images of the beating heart can even be made when the heartbeat is fast or irregular. Additionally, the use of two x-ray units allows for dual energy imaging that enables a better differentiation of the chemical composition of investigated structures.
Bayer HealthCare Pharmaceuticals is collaborating with Siemens AG to jointly develop contrast media application protocols for Siemens’ DSCT system Somatom Definition to provide radiologists with reliable protocol recommendations for scanner use and optimized contrast media injection parameters. The results were published in 2008 (“Dual Source CT Imaging”, Springer Medizin Verlag Heidelberg).
PET-CT fusion imaging
A recent development in diagnostic imaging is jointly involving computed tomography along with positron emission tomography (PET). PET-CT fusion imaging combines the strengths of two imaging modalities in a single comprehensive examination. While CT visualizes anatomical and morphological structures, PET detects pathological changes on a molecular level. Using both modalities together results in more information for a precise diagnosis.
Angiography
The radiological procedure which investigates the condition of blood vessels is called angiography. A distinction between arteriography and venography is usually made, depending on whether arteries or veins are being examined.
Digital subtraction angiography (DSA)
DSA is an optimization of classical Angiography. In DSA, the image is produced by subtracting radiographs without contrast media from radiographs taken after contrast media have been administered. The result of this subtraction process is the visualization of vessels filled with contrast media free from overlying structures. These procedures involve the use of specialized electronic equipment, including computing and radiographic hardware, to produce rapid sequential images.
Catheter-based coronary angiography
Coronary angiography or arteriography is an invasive method that involves a catheter. It is an x-ray examination of the blood vessels or chambers of the heart. A thin flexible plastic tube (catheter) is inserted into a blood vessel in the upper thigh or arm. The tip of the tube is positioned either in the heart or at the beginning of the arteries supplying the heart, and a contrast medium is injected. Depending on the discoveries during the angiography, additional catheter procedures may be performed at the same time, such as a balloon angioplasty or stent placement to open up a narrowed artery.
Intravenous urography (intravenous pyelography, IVU, IVP)
Intravenous urography remains the basic radiological examination of the urinary tract and its main purpose is to assess the shape, structure and the function of kidneys. When injected intravenously, most contrast media are rapidly excreted by the kidney, so a series of radiographs taken after the injection will highlight the urinary tract (kidney, ureter, bladder).
Interventional techniques
A lot of radiologists are now specializing in therapeutic procedures that have been developed from radiological techniques. These procedures include the widening of narrowed arteries (angioplasty, percutaneous transluminal angioplasty, PTA) as well as the deliberate closure of arteries supplying abnormal areas such as tumors, aneurysms and vascular malformations. Additionally biopsies and therapeutic treatments as e.g. radiofrequency ablations can be performed under CT control in order to increase the preciseness of the procedure.
Contrast media are often required to monitor the course and success of these treatment procedures.
