W Pavlicek

Digital substraction angiography in the evaluation of intracranial and extracranial vascular disease

Digital subtraction angiography (DSA) is a method of visualizing the vessels of the body with the intravenous injection of contrast material. Improvements in computers, television systems, and image intensifiers have contributed to the increased image quality of DSA. With DSA, the vessels such as the carotid bifurcations and the intracranial vasculature can be visualized with a 2–3% concentration of contrast material, while with conventional angiography, the concentration of contrast in vessels is 40–50%. Using IV DSA, visualization of the carotid bifurcations is of good or excellent quality 85% of the time. In a high percentage of these cases, IV DSA replaces conventional angiography, although for imaging of the intracranial vessels, IV DSA is not as good as conventional angiography. In most tumor patients, however, conventional intracranial angiography is not needed because IV DSA combined with computed tomography gives sufficient information.

Intravenous Digital Angiography Of The Head And Neck: A Clinical Update

The clinical experience of DSA of the head and neck in more than 1,000 patients is presented. In a comparative study of 100 conventional carotid angiograms, the accuracy rate in evaluating extracranial carotids was 97% in technically satisfactory studies. Intra cranial vessels were examined in 55 patients with both conventional selective catheterization and intravenous DSA. In 65% of the patients, the DSA examination was diagnostic. DSA is a safe, rapid procedure that can be performed on an outpatient basis and provides diagnostic information comparable to conventional angiography.

Architectural Considerations in a Medical Magnetic Resonance Imaging Facility

Initial discussions were carried out in May of 1981 regarding a suitable site for magnetic resonance imaging facility. At that time minimum information was available regrading the special environmental demands required for this new diagnostic modHlity. What was known for certain was that the whole body superconducting magnets were physically large (8 x 8 feet) and could not be delivered in a conventional elevator or through standard passage ways. The weight of a large superconducting magnet (fifteen thousand pounds) also precluded the siting of this unit above grade except in cases of special load bearing floors. For this reason it was decided to initiate discussions with an architectural firm to arrive at a suitable design for a standalone medical magnetic imaging facility. Initially, the siting criteria were based upon magnetic field strengths from two units of between 0.15 and 3.5 Tesla. In time however, discussions centered upon placing two magnets of 0.5 and 1.5 Tesla with a design basis for the facility of two units of 3.0 Tesla each.

Performance Specifications of a 0.15 Tesla Medical Magnetic Resonance Unit

In October 1982, medical magnetic resonance (MMR) clinical trials were initiated using a 0.15 Tesla resistive magnet. Measurement of standard image quality parameters were attempted in the first months following the installation. MMR signal strength is a complex interaction of tissue Tl, T2, spin density, and flow (including diffusion). Further, the operator selectable controls of TE (time to echo), TR (repetition time), and TI (inversion time) all tend to complicate any unique specification of the MMR signal. However, MMR can be approached from a conventional tomographic imaging problem. Image quality in MMR1suffers from partial volume affects and thus spatial resolution including slice thickness must be specified. System noise with MMR differs from all other conventional radiographic imaging modalities in that the sgurce of noise does not include a component that is derived from the statistical nature of the signal. Uniformity of signal response over an imaging volume in MMR is a prerequisite for quality examinations. Failure of the RF coil to provide a uniform secondary magnetic field results in a tip angle of other than the desired value. The spatial dependency of the secondary magnetic field is a function of the coil design.