Reduced-Dose CT: Effect on Reader Evaluation in Detection of Pulmonary Embolism
John D. MacKenzie1,2,
Javier Nazario-Larrieu1,3,
Tianxi Cai4,
M. Stephen Ledbetter1,
Maria Alejandra Duran-Mendicuti1,
Philip F. Judy1 and
Frank J. Rybicki1
1 Department of Radiology, Brigham and Women's Hospital, Boston, MA.
2 Present address: Department of Radiology, Lucile Packard Children's Hospital,
725 Welch Rd., Stanford, CA 94305H5654.
3 Present address: Department Radiology, Baylor College of Medicine, Houston,
TX.
4 Department of Biostatistics, Harvard School of Public Health, Boston,
MA.
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Fig. 1A —Effect of simulated dose. Graphs show effect of simulated
dose on diagnostic certainty (A) and image quality (B). For
particular level of simulated dose, bars represent proportion of patients at
each subjective reader score for diagnostic certainty (pulmonary embolus vs no
pulmonary embolus) and image quality. Proportions are average of four readers.
Brackets represent significantly different distributions between groups
(asterisk, p < 0.02, pound sign, p <0.01).
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Fig. 1B —Effect of simulated dose. Graphs show effect of simulated
dose on diagnostic certainty (A) and image quality (B). For
particular level of simulated dose, bars represent proportion of patients at
each subjective reader score for diagnostic certainty (pulmonary embolus vs no
pulmonary embolus) and image quality. Proportions are average of four readers.
Brackets represent significantly different distributions between groups
(asterisk, p < 0.02, pound sign, p <0.01).
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Fig. 2 —Graph shows effect of simulated dose on mean number of
perceived technical limitations (sum of motion artifact, image noise, body
habitus, poor timing of bolus contrast injection, and other). Brackets
represent comparisons between groups with significant differences for
distribution of technical limitations (asterisk, p < 0.01). Error
bars represent upper bounds of SD.
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Fig. 3 —Histogram shows distribution of clot burden measured with
pulmonary embolism (PE) index. All study patients with PE had low to moderate
clot burden ( 50% clot burden). Patients with low clot burden were more
likely to have PE missed at simulated low-dose examination (p <
0.04). Open bars indicate all study patients with PE. Solid bars indicate
patients with PE who had false-negative findings on at least one examination
at any simulated dose level. Each bar represents number of patients.
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Fig. 4A —Validation of simulation software for dose reduction. Pixel
noise is SD in Hounsfield units (average, 60 H) at region of interest obtained
in homogeneous portion of CT phantom. Graph shows simulated dose reduction and
dose reduction applied at CT scanner are tightly correlated (Pearson's
r = 0.99).
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Fig. 4B —Validation of simulation software for dose reduction. Pixel
noise is SD in Hounsfield units (average, 60 H) at region of interest obtained
in homogeneous portion of CT phantom. Graph shows relation between image noise
and dose reduction applied at CT scanner follows trend similar to that of dose
reduction simulated with software by mathematical addition of
gaussian-distributed quantum noise to raw CT data before image reconstruction.
Solid line with circles indicates CT scanner; dashed line with triangles,
simulation software.
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Fig. 5A —68-year-old woman with pulmonary embolism. Axial CT images at
simulated one-half dose (90 mAseff) (A) and lowest dose (10
mAseff) (B) and adequate contrast opacification show emboli
(arrows, A) in segmental arteries of right lower lobe
consistently identified by all four radiologists.
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Fig. 5B —68-year-old woman with pulmonary embolism. Axial CT images at
simulated one-half dose (90 mAseff) (A) and lowest dose (10
mAseff) (B) and adequate contrast opacification show emboli
(arrows, A) in segmental arteries of right lower lobe
consistently identified by all four radiologists.
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Fig. 6A —64-year-old man with pulmonary embolism. Axial CT images at
simulated one-half dose (90 mAseff) (A) and lowest dose (10
mAseff) (B) illustrate how technical factor limits detection
of pulmonary embolism on low-dose images. Diagnosis of pulmonary embolism,
including right lower lobe embolus (arrowhead, A) was missed
by two of four readers at lowest dose. All four readers rated study as
technically inadequate owing to improper timing of bolus administration of IV
of contrast material.
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Fig. 6B —64-year-old man with pulmonary embolism. Axial CT images at
simulated one-half dose (90 mAseff) (A) and lowest dose (10
mAseff) (B) illustrate how technical factor limits detection
of pulmonary embolism on low-dose images. Diagnosis of pulmonary embolism,
including right lower lobe embolus (arrowhead, A) was missed
by two of four readers at lowest dose. All four readers rated study as
technically inadequate owing to improper timing of bolus administration of IV
of contrast material.
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Copyright © 2007 by the American Roentgen Ray Society.
