Findings Regarding an Intracranial Hemorrhage on the Phase Image of a Susceptibility-Weighted Image (SWI), According to the Stage, Location, and Size

Abstract

Purpose: Susceptibility weighted imaging (SWI) is a new magnetic resonancetechnique that can exploit the magnetic susceptibility differences of various tissues. Intracranial hemorrhage (ICH) looks a dark blooming on the magnitude images ofSWI. However, the pattern of ICH on phase images is not well known. The purpose ofthis study is to characterize hemorrhagic lesions on the phase images of SWI. Materials and Methods: We retrospectively enrolled patients with ICH, whounderwent both SWI and precontrast CT, between 2012 and 2013 (n = 95). AnSWI was taken, using the 3-tesla system. A phase map was generated after postprocessing. Cases with an intracranial hemorrhage were reviewed by an experiencedneuroradiologist and a trainee radiologist, with 10 years and 3 years of experience,respectively. The types and stages of the hemorrhages were determined in correlationwith the precontrast CT, the T1- and T2-weighted images, and the FLAIR images. Thesize of the hemorrhage was measured by a one- directional axis on a magnitude imageof SWI. The phase values of the ICH were qualitatively evaluated: hypo-, iso-, andhyper-intensity. We summarized the imaging features of the intracranial hemorrhageon the phase map of the SWI. Results: Four types of hemorrhage are observed: subdural and epidural; subarachnoid;parenchymal hemorrhage; and microbleed. The stages of the ICH were classifiedinto 4 groups: acute (n = 34); early subacute (n = 11); late subacute (n = 15);chronic (n = 8); stage-unknown microbleeds (n = 27). The acute and early subacutehemorrhage showed heterogeneous mixed hyper-, iso-, and hypo-signal intensity;the late subacute hemorrhage showed homogeneous hyper-intensity, and the chronichemorrhage showed a shrunken iso-signal intensity with the hyper-signal rim. Allacute subarachnoid hemorrhages showed a homogeneous hyper-signal intensity. Allparenchymal hemorrhages (> 3 mm) showed a dipole artifact on the phase images;however, microbleeds of less than 3 mm showed no dipole artifact. Larger hematomasshowed a heterogeneous mixture of hyper-, iso-, and hypo-signal intensities. Conclusion: The pattern of the phase value of the SWI showed difference, accordingto the type, stage, and size.