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Updates on Canine Brain tumors:
options to make the diagnosis (part 2)

➤ Continued from Front Cover
flm. The word tomography is derived from CT technology. Multidetector CT scanners are sults in the emission of a detectable RF signal
the Greek tomos (slice) and graphein (to write). similar in concept to the helical or spiral CT that is received by the RF coil and transmitted
The frst viable CT scanner was made possible but there is more than one detector ring. The to a computer for image generation. Since pro-
only after signifcant advances in computer major beneft of multidetector CT scanning is tons in different tissues of the body realign at
processing technology were made. Today, the increased speed of volume coverage. This different rates, the RF signal that is received
allows large volumes to be scanned at the by the RF coil can be fltered to accentuate
optimal time following intravenous contrast different tissue characteristics using specifc
At LIVS, we routinely administration. At LIVS, we routinely use our sequences. Additionally, contrast agents
use our multidetector multidetector CT in cases involving tumors of may be processes.
the skull. From this, a 3-dimensional model
The two most important determinants of
CT in cases involving can be constructed and displayed on screen. the quality of the MRI service rendered to a
tumors of the skull. Multiple models can be constructed from vari- patient are 1) magnet strength (measured in
ous thresholds, allowing different colors to Tesla units, abbreviated as T) and 2) training
represent each anatomical component such and experience level of the MR machine opera-
computed tomography is a commonly utilized as skin (Figure 2a), muscle (Figure 2b), bone tors. In order to keep costs at a minimum, many
medical imaging method employing tomogra- (Figure 2c), including 3D diagrams (Figure 2d) veterinary referral centers maintain low feld
phy principles where digital processing is used and surgical models (Figure 2e). strength magnets (0.3-0.5 T), whereas others
to generate a three-dimensional image of a will invest in a more robust magnet (1.5 T is
subject from a large series of two-dimensional Magnetic Resonance Imaging considered a standard magnet size for most
X-ray images taken around an axis of rota- The superior detail afforded by MR imaging clinical applications). At Long Island Veterinary
tion. Images can be manipulated, through a makes it the preferred choice for imaging the Specialists, we have invested in a 3T magnet,
computerized process known as windowing, brain. Magnetic resonance imaging is based the only 3T system in private veterinary prac-
in order to reveal various structures based on on the detection of radiofrequency signals tice, offering unmatched resolution and speed
tissue characteristics. With recent advances emitted from a patient and the conversion of (Figure 3a & b). The merits and limitations of
in technology, modern scanners allow this those signals into a computerized gray-scale the different strength MR systems will be the
data to be reformatted as volumetric (3D) rep- image or tomogram. When a patient is placed subject of a subsequent newsletter article.
resentations of structures. Helical or Spiral in a scanner, the hydrogen nuclei or protons, Also, it is common practice for veterinary
CT was introduced in the early 1990s. In heli- found mostly in water molecules of the body, referral centers to have veterinary technicians
cal CT, the table moves the patient smoothly align with the main magnetic feld. A second complete a short training program (e.g., 2-3
through the scanner with the X-ray source electromagnetic feld produced by the radiofre- weeks) and then operate the MR machine. Al-
attached to a freely rotating gantry. The major quency (RF) coil, which is perpendicular to the though reasonable images are often obtained
advantage of helical scanning compared to main feld, is then pulsed to further polarize with this approach, such operators are often
the traditional CT scanning is speed; a large the protons out of alignment with the main learning as they go (on clinical patients) and
volume can be scanned quickly. Additionally, feld. These protons are then permitted to drift are less fexible than certifed MRI technolo-
the data obtained from spiral CT is often well back into alignment with the main magnetic gists with what they can accomplish-even with
suited for 3D imaging, which led to the rapid feld between RF pulses. The subsequent re-
rise of helical CT as the most popular type of laxation of the protons back into alignment re- Continued on Page 6 ➤

Figure 2a-e 3-Dimensional image reconstruction utilizing
multidetector CT demonstrating multiple layers of tissue that
can be removed via post processing, as well as 3D modeling.

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