Radiologic Testing: What, When, & Why

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Radiologic Testing What, When, Why

• Harry Colt, MD
• 7/20/09

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Why This is an Important Topic

• Radiology skills are underemphasized in medical
  school
• Radiology was a relatively weak part of our
  curriculum
• Most of our focus is on interpretation of X-rays
• Deciding what film to order is as important as
  interpreting the film
• Residents now do a 2 week radiology rotation in
  year 3

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• Objective
• Participants will be able to identify appropriate
  
• X-ray tests for many common clinical
• conditions

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• Methods
• Brief orientation and review of the 7 main
  radiologic testing modalities
• Case based approach

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Radiation
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Prices
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Prices
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Prices
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Prices
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• Seven Radiologic Modalities
• plain films
• Contrast Agents
• CT scans
• Ultrasound
• Nuclear Imaging
• Magnetic Resonance Imaging
• PET Scan

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Plain Films

• image formed by attenuation of x-rays by the
  material that they are passing through
• the denser the material, the greater the
  attenuation, the lighter the image will be
• the four basic densities in order of increasing
  density air, fat, water (blood, soft tissue),
  bone. Its the contrast between these densities
  that delineates structures
• plain films are 2D pictures of 3D structures, so
  multiple views generally needed

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Contrast Agents

• plain films are useful in situations where there
  is a natural contrast between body structures
  (e.g., heart lung)
• If no inherent contrast, contrast agents can help
  (esp. GI, urinary tract, and vasculature)
• Disadvantages
• -5-10 have mild reaction feel warm, metallic
  taste, etc
• -0.1 have severe reaction syncope,
  anaphylaxis, hypotension
• -with low-osmolality agents, only 2 have
  reactions, but costs up to 10 times as much
• -with IV contrast, increased risk of
  nephrotoxicity in patient with Cr1.5,
  particularly if diabetic

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• CT Scans
• Rotating beam of x-rays that pass through patient
  and computer calculates absorption at thousands
  of points
• Most organs (heart, kidney, liver, spleen,
  pancreas, etc.) are of uniform density and
  produce grey image on plain film. CT provides
  shades of grey.
• Traditional CT takes pictures like slices of
  loaf of bread

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• CT Scans contd
• Spiral CT pictures taken like paring of apple
• Advantages of CT
• -differentiate structures of similar density
• -view multiple structures simultaneously
• Disadvantage
• -many times the radiation of plain films
• (see slide 5)
• -generally need IV contrast with CT unless
  ruling out CNS bleed, ureteral stone protocol,
  or sinus views

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• Ultrasound
• emits high frequency sound waves, assesses the
  strength and timing of returning echoes
• us waves greatly reflected by air soft tissue
  and bone soft tissue interfaces, limiting its
  use in the chest and bones

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• Ultrasound contd
• Advantages
• -no radiation (safe in obstetrics)
• -good for rapidly moving structures (e.g.,
  heart)
• Disadvantages
• -limited in chest and bones
• -operator dependent

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• Nuclear Imaging
• Takes advantage of selective uptake of certain
  compounds in different organs of the body
• These compounds can be labeled by radioactive
  isotopes
• Their uptake can be recorded by a gamma camera
  that records radiation
• Advantages
• -can obtain an image of function
• Disadvantages
• -radiation (see slide 5)
• -cost

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• MRI (Magnetic Resonance Imaging)
• Applies magnetic field to the body. When field
  released, radio waves generated
• Advantages
• -no ionizing radiation
• -extraordinary views of CNS stationary soft
  tissues
• -contrast (Gadolinium) generally not needed
  unless MRA-neck, or MRI-head to rule out tumor
• Disadvantages
• -inability to bring ferrous objects near magnet
• -contraindications pacer, defibrillator,
  aneurysm clips
• -must hold still
• -if gadolinium used, risk of nephrogenic
  systemic fibrosis in patients with renal failure

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PET Scan

• Allows imaging of structures based on their
  ability to concentrate specific molecules that
  have been labeled by positron emitting isotope
• PET better than CT at differentiating benign from
  malignant lesions

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Case 1 (Low Back Pain) 48 yo man presents with a
2 day history of severe low back pain radiating
down posterolateral aspect of right leg to foot.
Developed after gardening all day. No prior back
problems. On exam in obvious discomfort with
movement. He has no neurologic deficits. Does he
need imaging procedure? Why?
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Case 1 (Low Back Pain) The patient returns one
week later with unchanged symptoms and
exam. Does he need imaging procedure? If so,
what type? Why?
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• Case 1 (Low Back Pain)
• Ninety plus percent of these patients recover
  spontaneously
• Consider MRI at 6 weeks if not improving
• Early plain films (300) or MRI (1600) indicated
  only if suspicion of fracture (significant recent
  trauma), infection, cancer, or progressive
  neurologic loss
• Contd

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• Contd
• Without these suspicions, early MRI results in
  increased frequency of surgical procedures, but
  no improved outcome
• MRIgt in asymptomatic individuals
• -52 with symmetric disc bulges
• -27 with asymmetric disc bulging
• -10 with disc extrusion
• -75-80 of asymptomatic men over age 50 have
  disc bulging

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Case 2 (Diabetic Foot Ulcer) 66 yo diabetic
woman presents with 1 week history of 2cm
ulceration on right foot. Does her foot need
imaging? Why? Contd
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• Contd
• If so, what technique? plain films, bone scan, or
  MRI?
• Diabetic Foot Ulcers
• in diabetic foot ulcers larger than 2cm2, 68
  have osteomyelitis by bone biopsy and culture
• Most have no sign of inflammation on exam

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• Case 2 (Diabetic Foot Ulcer)-contd
• plain Films (271)
• Can identify soft tissue swelling, bone
  destruction, periosteal elevation
• insensitive for acute Osteomyelitis. 2-3 weeks
  usually needed to see bony changes
• Even after 3 weeks, sensitivity approaches 60-80
• Contd

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• Contd
• 3 Phase Bone Scan (900)
• Technetium bound to phosphorus, and accumulates
  in areas of increased osteoblastic activity
• 3 phases
• -1st phase immediate reflects flow
• -2nd phase 15 min. reflects blood pooling
• -3rd phase 4 hours bone imaging
• contd

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• Contd
• 3 Phase Bone Scan
• Cellulitis has increased activity in phases 1 and
  2
• Osteomyelitis has intense uptake in all 3 phases
• Often times positive in acute osteo by 3 days
• Imaging procedure of choice for acute
  osteomyelitis
• Contd

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• Case 2 (Diabetic Foot Ulcer)-contd
• MRI (1500)
• can be very useful in infected diabetic foot
• Sensitivity 95
• Imaging test of choice for chronic osteo

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Case 3 (Abdominal Pain) 54 yo woman presents
with 3 day history of upper abdominal pain,
nausea, and occasional vomiting. On exam Temp.
100o, tender in RUQ,. Labs wbc 14.8, normal
LFTs, lipase, and amylase. What is the most
likely diagnosis? What is your imaging procedure
of choice? Why?
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• Case 3(cholecystitis)
• Ultrasound (698)
• can identify stigmata of cholecystitis
• -gallstones
• -gallbladder wall thickening (gt4-5 mm)
• -gallbladder wall edema (double wall sign)
• -sonographic Murphys sign
• For cholecystitis sensitivity 88, specificity
  80
• Can miss very small stones (lt3mm)

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If ultrasound negative, what might you do next?
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• Case 3 (Cholecystitis)-contd
• Cholescintigraphy (HIDA scan) (1200)
• Use technetium labeled hepatic iminodiacetic acid
• Injected IV, taken up by hepatocytes and excreted
  in bile
• If the cystic duct is patent, it will enter
  gallbladder
• Test is positive (abnormal) if gallbladder not
  visualized, usually due to cystic duct
  obstruction from edema from cholecystitis or
  stone
• Sensitivity 97, specificity 90

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Case 4 (Hip Injury) 88 yo male presents with hip
pain after fall last night. On exam complains
of pain with any movement of hip. Initial hip
films are inconclusive for fracture. What is the
imaging test of choice when hip fracture is
suspected, but plain films are negative?
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• Case 4 (Hip Injury)-contd
• MRI (1500) is study of choice
• Bone scan (1100) indicated for suspected
  fracture when MRI not available or
  contraindicated
• CT (1200)

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Case 5 (Diverticulitis) 77 yo man presents with
LLQ pain and nausea for 2 days. On exam has temp
of 101o, LLQ tenderness. What is imaging
procedure of choice?
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• Case 5 (Diverticulitis)
• plain films? (475) No
• abdominal films usually only helpful when you
  suspect obstruction or significant perforation
• CT? (1631) Yes
• Helical CT with contrast sensitivity 97 for
  diverticulitis features include increased soft
  tissue density secondary to inflammation
  (greying of fat), colonic diverticula, bowel
  wall thickening, soft tissue masses
• Contrast Enema? (900) In rare cases
• Would use water soluble contrast given risk of
  perforation.

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Case 5A (Diverticulitis) same patient 77 yo
man with diabetes with LLQ pain and nausea for 2
days. On exam has temp of 101o, LLQ
tenderness. Creat 1.8. What is the imaging
procedure of choice?
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Discuss with radiologist CT without IV contrast
vs CT with contrast vs MRI without contrast or
US If opt for CT with contrast, patient
needs -ISO osmolal agent -avoid volume
depletion and NSAIDS -if no
contraindictions, IV isotonic fluids -conside
r acetylcystine
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Case 6 (Sinusitis) 34 yo female presents with 3
week history of nasal congestion maxillary
tenderness. Believes she has recurrence of
sinusitis. Does she need imaging?
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• Case 6 (Sinusitis)
• If patient believed to have sinusitis, would
  treat without imaging.
• If fails treatments, then CT is imaging procedure
  of choice.
• plain sinus films (3v) (372) have low
  sensitivity
• CT (960) much more sensitive, but gives false
  positives. 27/31 false positives in 1 study of
  patients with cold. Dont order early in course
  of illness, you will only generate unhelpful
  information.

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Case 7 (Urolithiasis) 64 yo man presents with 1
day history of severe left flank pain. Never had
similar symptoms previously. On exam, his abdomen
is nontender, no prominent abdominal pulsation.
Urine shows microscopic hematuria. You suspect
ureteral stone. What is imaging procedure of
choice?
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• Case 7 (Urolithiasis)-contd
• KUB (abdominal film) (238)-No
• May show calcium containing stones, misses
  radiolucent (uric acid) stones and small stones.
• Will not identify obstruction

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• Case 7 (Urolithiasis)-contd
• IVP (800)
• High sensitivity and specificity
• Can cause renal injury due to dye load
• Replaced by noncontrast helical CT (1200)

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• Case 7 (Urolithiasis)
• Non contrast helical CT (1200)
• Detects stones and obstruction
• 95 sensitivity, 98 specificity significantly
  better than IVP in meta-analyses
• Advantages
• -faster
• -better
• -no dye load
• Disadvantage
• -can sometimes have difficulty differentiating
  ureteral stone from phlebolith

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Case 8 (Hematuria) 74 yo woman with asymptomatic
microscopic hematuria discovered on UA. History
of tobacco abuse. She needs cystoscopy and an
imaging procedure. Which imaging procedure makes
most sense?
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• Case 8 (Hematuria)
• Studies suggest non contrast CT (1200) is more
  sensitive and specific than IVP
• CT sensitivity 98 plus percent, specificity 97
• IVP sensitivity 61 percent, specificity 91

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Case 9 (Pancreatitis) 42 yo woman with upper
abdominal pain for 2 days, nausea, and vomiting.
She is s/p cholecystectomy. Exam notable for mild
upper abdominal tenderness. wbc 14,000, normal
LFTs, lipase 1680. Does she need imaging? If so,
what test and why?
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• Case 9 (Pancreatitis)-contd
• plain films (475)
• Will primarily rule out obstruction and bowel
  perforation
• May demonstrate ileus of segment of small
  intestine (sentinal loop)
• Generally not helpful in pancreatitis

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• Case 9 (Pancreatitis)-contd
• Ultrasound (698)
• May demonstrate diffusely enlarged pancreas
• In 1/3 of patients unable to visualize pancreas
  well, due to bowel gas or obesity
• Cannot identify necrosis in pancreas
• Can identify stone in gallbladder

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• Case 9 (Pancreatitis)-contd
• CT (1631)
• Generally, visualizes pancreas well.
• Can determine whether necrosis present
• Indicated in those who are not improving or in
  whom complications suspected.
• MRI MRCP (1800)
• delineates pancreatic and bile ducts well
• Will likely replace CT as test of choice in future

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Case 10 56 yo man with upper abdominal pain for
2 days, with nausea and vomiting. He is s/p
cholecystectomy. Exam notable for mild upper
abdominal tenderness. Wbc 14,000. AST 216, ALT
244, lipase 1680. Does he need imaging? If so,
what testing and why?
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• MRCP (1435)
• delineates pancreatic and bile ducts well
• useful if concerned about possible CBD stone
• ERCP
• indicated if CBD stone believed likely

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Case 11 (Ankle sprain) 16 yo comes in after
suffering sprain of ankle while playing soccer.
On exam, has swelling over lateral malleolus. No
localizing tenderness. Limps, but can walk across
room. Does he/she need ankle films
(271)? Contd
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• Ottawa Rules for Ankle Injury
• 27 studies of over 15,000 patients
• Over 98 sensitivity for fracture
• Ankle x-rays (271) indicated if
• pain and either
• 1. bony tenderness at posterior edge or tip
  of either malleous
• or
• 2.unable to bear weight after injury and for
  4 steps in office
• contd

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• contd
• Foot x-ray (271) if
• pain in mid foot and
• 1. bony tenderness at base of 5th
  metatarsal or navicular
• or
• 2. unable to bear weight after injury and
  walk 4 steps in ER.
• So when seeing patient with ankle sprain
• check for pain, tenderness, bear weight after
  injury, and 4 steps in your office to help
  decide whether x-ray needed.

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Case 12 82 yo with H/O CAD, A fib on coumadin
presents with left hemiparesis for 6 hours. On
exam BP 188/100, findings of left hemiparesis,
cor irregularly irregular. What is the imaging
procedure of choice?
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Non contrast Head CT (1208) 1) exclude
hemorrhage 2) at 6 hours 50 of NCH CT have
abnormalities c/w stroke (eg., hypodensity,
focal brain swelling) 3) pro rapid scan
times ease of detecting
hemorrhage availability
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Case 13 18 yo with 2 day H/O abdominal pain. T
99.6. Tender in RLQ. Wbc 12,000. You suspect
appendicitis. Does the patient need an imaging
procedure?
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If diagnosis uncertain CT (1631) sensitivity
94 specificity 95 US (698) sensitivity
86 specificity 81
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Case 14 34 yo slips on ice striking head on
pavement. Comes to MDFP to be seen. Friend
reports patient unconscious for 30 sec. Patient
does not recall the 5 min. prior to the fall. No
headache or vomiting. GCS 15. Normal neurologic
exam Do you send her for CT?
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New Orleans Criteria

• CT needed after minor head injury (GCS15) if (1
  or more of the following)
• Headache
• Vomiting
• Age gt60
• Drug or alcohol intoxication
• Persistent antegrade amnesia (deficits in short
  term memory)
• Visible trauma above clavicle

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Canadian CT Head Rule

• CT needed after minor head injury (GCS15) and (1
  or more of the following)
• Suspected or depressed skull fracture
• Any sign of basal skull fracture
• 2 or more episodes of vomiting
• Age 65
• Amnesia before impact of gt30 min.
• Dangerous mechanism (eg. MVA, fell from height,
  etc.

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• Summary
• Before ordering a radiologic test, consider which
  test is most appropriate and whether its likely
  to alter management.
• Include pertinent clinical information, so
  radiology dept./radiologist can let you know if
  another test would be better.
• Contact radiologic consultant if you are unsure
  what to order.