title: Exposing hidden truncation-related errors in acute stroke perfusion imaging.
abstract: OBJECTIVE
  The durations of acute ischemic stroke patients' CT or MR perfusion scans may be too short to fully sample the passage of the injected contrast agent through the brain. We tested the potential magnitude of hidden errors related to the truncation of data by short perfusion scans.
  
  
  METHODS
  Fifty-seven patients with acute ischemic stroke underwent perfusion MR imaging within 12 hours of symptom onset, using a relatively long scan duration (110 seconds). Shorter scan durations (39.5-108.5 seconds) were simulated by progressively deleting the last-acquired images. CBV, CBF, MTT, and time to response function maximum (Tmax) were measured within DWI-identified acute infarcts, with commonly used postprocessing algorithms. All measurements except Tmax were normalized by dividing by the contralateral hemisphere values. The effects of the scan duration on these hemodynamic measurements and on the volumes of lesions with Tmax of >6 seconds were tested using regression.
  
  
  RESULTS
  Decreasing scan duration from 110 seconds to 40 seconds falsely reduced perfusion estimates by 47.6%-64.2% of normal for CBV, 1.96%-4.10% for CBF, 133%-205% for MTT, and 6.2-8.0 seconds for Tmax, depending on the postprocessing method. This truncation falsely reduced estimated Tmax lesion volume by 71.5 or 93.8 mL, depending on the deconvolution method. "Lesion reversal" (ie, change from above-normal to apparently normal, or from >6 seconds to ≤6 seconds for the time to response function maximum) with increasing truncation occurred in 37%-46% of lesions for CBV, 2%-4% for CBF, 28%-54% for MTT, and 42%-44% for Tmax, depending on the postprocessing method.
  
  
  CONCLUSIONS
  Hidden truncation-related errors in perfusion images may be large enough to alter patient management or affect outcomes of clinical trials.
authors.affiliation: From the Departments of Radiology (W.A.C., A.R.D., P.W.S., R.G.G., O.W.) wcopen@partners.org.
authors.forename: W A
authors.initials: WA
authors.lastname: Copen
authors.affiliation: From the Departments of Radiology (W.A.C., A.R.D., P.W.S., R.G.G., O.W.).
authors.forename: A R
authors.initials: AR
authors.lastname: Deipolyi
authors.affiliation: From the Departments of Radiology (W.A.C., A.R.D., P.W.S., R.G.G., O.W.).
authors.forename: P W
authors.initials: PW
authors.lastname: Schaefer
authors.affiliation: Neurology (L.H.S.), Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts.
authors.forename: L H
authors.initials: LH
authors.lastname: Schwamm
authors.affiliation: From the Departments of Radiology (W.A.C., A.R.D., P.W.S., R.G.G., O.W.).
authors.forename: R G
authors.initials: RG
authors.lastname: González
authors.affiliation: From the Departments of Radiology (W.A.C., A.R.D., P.W.S., R.G.G., O.W.).
authors.forename: O
authors.initials: O
authors.lastname: Wu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000098:blood supply; D002545:Brain Ischemia / Q000175:diagnosis*; D002560:Cerebrovascular Circulation / Q000502:physiology; D003951:Diagnostic Errors; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods; D005260:Female; D006439:Hemodynamics; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D055420:Perfusion Imaging / Q000379:methods*; D020521:Stroke / Q000175:diagnosis*; D013997:Time Factors