Jorg F. Debatin – författare

One of the most amazing and spectacular developments in modern radiology has been the rapid growth and expansion of so-called interventional radiology, which can also be described as minimally invasive therapy guided by radiological imaging. Many applications of this method are now widely in use in different organs, particularly in the vascular system. Everybody is well aware of the shortcomings and drawbacks of the radiological modalities currently used for guiding minimally invasive procedures. Ultrasound, although it has the advantage of being absolutely harmless to the patient and the operator, cannot be used for many procedures because it does not provide the precise anatomical information needed for a safe performance of these procedures. Rontgen rays provide superb anatomical insight to guide delicate manipulations inside the human body, but as operations tend to become longer and more complicated, the radia­ tion dose for patients, as well as for operators, is becoming an increasing source of concern. It is therefore logical that we should explore the possibilities for interventional radiological procedures provided by the latest imaging modality -magnetic resonan­ ce imaging -taking advantage of the specific physical properties of this method and the absence of ionizing radiation. It soon became evident that this new approach represents a tremendous challenge involving the development of new hardware and software, new catheters and other material that can be used in a magnetic environment, etc.

The imaging potential of the MR experiment continues to evolve. In recent years, an increasing number of fast and ultrafast imaging strategies has been described. In this evolu­ tion the definition of the terms fast and ultrafast has been blurred. Hence they are frequently used interchangeably. The evolution of these methods has been based on two related, yet separate developments: an increasingly thorough understand­ ing of the complexities inherent to pulse sequence design and the increasing availability of stronger and faster gradient sys­ tems. The combination of these two factors has laid the foun­ dation for vast reductions of MRI data acquisition times. Min­ utes have been replaced by seconds. Beyond shortening MR examination times and thereby increasing patient throughput, a most significant consequence has been the ability to acquire complex MR image sets within the time confines of a single breath-hold. The constraints placed by the presence of respi­ ratory motion have thus been effectively eliminated. Ultrafast breath-held data acquisition strategies already represent the backbone of many abdominal, thoracic and even pelvic imaging protocols. The enhanced image quality permits full exploitation of the unsurpassed soft tissue contrast inherent to the MR experiment. Beyond improving the quality of ex­ isting applications, the implementation of ultrafast imaging techniques has permitted the exploration of new imaging in­ dications, particularly in the area of perfusion and diffusion as well as ultrafast 3D imaging.

Non-invasive, high resolution contrast arteriography without arte rial catheterization or nephrotoxicity is now possible. It is accomplished by using paramagnetic contrast and an MR scanner. Paramagnetic contrast media is injected intravenously and image data are collected as the con­ trast circulates through the vascular territory of interest. Due to the strong enhancement effect of paramagnetic contrast media, a small dose injected as an intravenous bolus is sufficient to briefly enhance the entire arterial vascular tree. This allows imaging with a large field-of-view that encompasses an extensive region of vascular anatomy. By using a 3D gradient echo pulse sequence on magnets with high performance gra­ dient systems, high resolution 3D volumes of image data are acquired in a single breath-hold. This has vastly improved image quality of 3D con­ trast MRA exams, particularly in the chest and abdomen. Subsequent post-processing allows an angiographic display of image data in any desired obliquity. The success of this technique is reflected by its incorporation into clinical practice in centers throughout the world. It has been applied to multiple vascular territories, using various magnets, and slightly differ­ ing imaging strategies. As is the ca se for all MR imaging techniques, a thorough understanding of the underlying mechanisms and proper technique are essential to fully exploit the diagnostic potential of this new form of angiography. This book will familiarize the reader with the basic principles of 3D contrast MRA.