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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:

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To Contrast or Not To Contrast

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To contrast or not to contrast l.jpg

To Contrast or Not To Contrast

Cole Taylor, MD, HOIII


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Introduction

  • Electromagnetic Radiation

    • Visible light, X-rays, radio waves in magnetic resonance imaging

  • Ultrasound

    • Pressure Waves


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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.


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What is a voxel?


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Contrast Media

  • Negative Contrast Media

    • Air, CO2, gases

    • Attenuates X-Rays less than the soft tissues of the body (contain less per unit volume)


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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)


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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


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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.


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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


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  • 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.


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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


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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


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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)


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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


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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


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Guidelines

  • CT Pelvis

    • Oral contrast for all indications except kidney stones

    • Fracture – without contrast


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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


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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


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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


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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


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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


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Conslusions

  • Tumors always need contrast

  • MRI generally need contrast unless only evaluating bony structures

  • CT – tumor and infection always need contrast


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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


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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


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Questions?


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