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To-Contrast-or-Not-To-Contrast

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					To Contrast or Not To
      Contrast
   Cole Taylor, MD, HOIII
                 Introduction
   Electromagnetic Radiation
    – Visible light, X-rays, radio waves in magnetic
      resonance imaging
   Ultrasound
    – Pressure Waves
            Purpose of Contrast
   All contrast media in diagnostic imaging have
    one task:
    – To increase the differences between the different
      "voxels" in the body regarding their ability to absorb
      and/or reflect energy from electro-magnetic radiation
      or ultrasound.
    – A "voxel" in this context may mean any structure,
      such as a piece or slice of normal tissue, or a
      complete organ, etc.
    – Different contrast media influence electro-magnetic
      radiation or ultrasound by different mechanisms.
What is a voxel?
               Contrast Media

   Negative Contrast Media
    – Air, CO2, gases
    – Attenuates X-Rays less than the soft tissues of
      the body (contain less per unit volume)
        Positive Contrast Media
   Increased ability to attenuate X-Rays

   Ex: Iodine and barium have higher atomic
    numbers than those elements of the soft
    tissue (hydrogen, carbon, nitrogen,
    oxygen)
             More on Contrast
   Barium Sulfate
    – Large insoluble particles
    – Examination of upper and lower GI
    – Better coating properties than iodinated
      contrast
    – May cause chemical peritonitis if it escapes
      gut (DON’T USE WITH PERF)
    – Also may cause pulmonary edema if there is
      risk of aspiration
    Use of Contrast With GI Imaging
   Barium sulfate, the most common
    oral contrast agent, resembles a
    milk shake in appearance and
    consistency. The compound,
    available in various flavors, is
    prepared by mixing with water.

   Gastrografin is a yellowish,
    water-based drink mixed with
    iodine. It can have a bitter taste.
                Gastrografin
   Use with Small Bowel Obstruction
    – Six randomized studies dealing with the
      therapeutic role of gastrografin were included
      in the review, water-soluble contrast did not
      reduce the need for surgical intervention
    – Meta-analysis of four of the included studies
      showed that water-soluble contrast did reduce
      hospital stay compared with placebo
   Iodine Contrast
    – Forms soluble compounds with low toxicity
    – The iodine density blocks the passage of the
      x-ray photons, causing the contrast to appear
      denser (white) on the CT images
   Contrast media can be classified into ionic
    and nonionic media.
               MRI Contrast
   Since MRI is based on magnetization, not
    ionizing radiation, the intravenous contrast
    material must have magnetic properties
    different from that of the surrounding
    tissue. The most common agent used is
    gadolinium
    When to Use MRI Contrast
 Differentiation of tumor from edema
 Inflammation and soft tissue from scar
  tissue
 Dynamic assessment of lesion types
 Assessment of early ischemia
 Parenchymal brain infections
 Meningeal lesions
 Demyelinating lesions in MS
      Downside to Gadolinium
 36 of 21,000 patients experienced significant
  adverse reactions
 American Journal of Roentgenology, Vol 167,
  847-849

 However…lots of information on law suits is out
  there currently, affecting current use of
  gadolinium at UNMC.
 2006 – FDA releases warning - 25 cases of
  NSF/NFD in patients with kidney failure
  (Nephrogenic Systemic Fibrosis)
      Time for the Guidelines
 CT Head – almost always without contrast
  unless evaluating tumor (c and s)
 CT Sinus – without
 CT Maxillofacial – without
 CT Orbits/Sella/Ear – without except for
  cellulitis, tumor, neuroma, cholesteatoma
                  Guidelines
   CT Abdomen – oral contrast for all
    indications except Kidney Stones, IV
    contrast when indicated below
    – Kidney Stones – without
    – Pancreas, Liver, Renal Mass, Adrenal Mass –
      With and Without
    – Abdominal Pain – with only
    – Appendicitis – with only
    – In general, order with pelvis as well
                   Guidelines
   CT Pelvis
    – Oral contrast for all indications except kidney
      stones
    – Fracture – without contrast
                  Guidelines
   CT Chest
    – Generally with contrast (PE, SOB, Pain, PNA,
      Tumor, Trauma, Pneumo)
    – COPD – without
    – Pulmonary Nodules (follow-up) – without
    – Interstitial Lung Disease – without
    – Bronchiectasis - without
   CTA Chest – only done with contrast
                   Guidelines
   CT C-Spine, T-Spine, L-Spine
    – Generally done without (trauma, pain,
      fracture, weakness)
    – Tumor – with
    – Infection/Abscess - with
   CT Extremity
    – Generally done without
    – Tumor/Infection/Abscess - with
                MRI Guidelines
   MRI Brain
    – In general always with and without (HA,
      Trauma, MS changes, Dizzy, CVA, Weakness,
      Memory Loss)


 MRI Sinus – with and without (tumor)
 MRI Orbit/Sella/Ear – with and without
                  Guidelines
   MRI Abdomen (Including MRCP)
    – With and Without
    – Exception – Fetal MRI
   MRI Pelvis
    – Bony exams – without
    – Soft tissue exams – with and without
 MRI Cardiac – with and without
 MRA Chest – with only
                   Guidelines
   MRI C, T, L Spine
    – Generally done without
    – Tumor, Infection/Abscess, Metastases, CA
        With and Without
   MRI Extremity
    – Generally done without
    – Tumor, Infection/Abscess, CA – with/without
    – To follow arthrogram - with
              Conslusions
 Tumors always need contrast
 MRI generally need contrast unless only
  evaluating bony structures
 CT – tumor and infection always need
  contrast
     Renal Prophylaxis to Prevent
    Contrast Induced Nephropathy
 Primary benefit in patients with creatinine
  > 1.5 or GFR < 60, particularly in diabetic
  patients
 Optimal therapy remains uncertain
 If possible, use MRI without gadolinium,
  CT without contrast, or Ultrasound
 Avoid volume depletion and NSAIDs
        Renal Prophylaxis cont.
 Isotonic IV fluids prior to and for several
  hours following administration of contrast
 Uptodate current recs
    – Bolus of 3 mL/kg of isotonic bicarbonate for
      one hour prior to the procedure
    – Change to rate of 1 mL/kg per hour for six
      hours after the procedure
    – Solution can be prepared with 3 amps HCO3
      (150 mL) in 850mL D5W
Questions?

				
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posted:12/1/2009
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