ABSTRACT
To compare the accuracy of a three dimensional, T2-weighted double inversion recovery (DIR) sequence with two dimensional fluid attenuated inversion recovery (FLAIR) and dual echo T2 (DE T2) sequences at 3 Tesla in the detection of intracranial demyelinating lesions in patients with known or suspected multiple sclerosis (MS), and to consider the appropriateness of a stand-alone DIR sequence in MS imaging. The studies of 98 patients who underwent imaging with DE T2, FLAIR and DIR sequences for known or suspected multiple sclerosis were retrospectively reviewed. In 42 cases, a diagnosis of MS had been clinically suspected. In the remaining 56 cases, a diagnosis of MS had been previously established. All patients were imaged on a 3T MRI unit. Coronal and sagittal FLAIR, axial DE T2, and three dimensional T2-weighted DIR sequences were utilised. Of the 42 patients with suspected multiple sclerosis, 11 demonstrated lesions characteristic of the disease. Demyelinating plaques were seen in all of the 56 patients with known MS. In all cases, all lesions seen on DE T2-or FLAIR sequences were visible and more conspicuous on the DIR sequence. In 22 of the 67 patients (33%) with demyelinating lesions, the DIR sequence showed additional lesions not visible on any of the other sequences. Additional detected lesions predominantly involved grey matter. At 3 Tesla, a T2 weighted, three dimensional DIR sequence is as accurate at detecting the presence of intracranial demyelinating lesions as two dimensional FLAIR and DE T2 sequences combined. A greater number of lesions were detected with the DIR sequence, and all lesions were more conspicuous. A single, stand alone DIR sequence may be considered appropriate for monitoring MS.
ABSTRACT
Bronchoconstrictor responses are quantitatively different when they are evoked under static conditions and during or after periods of deep inspiration. In vivo, deep inspirations produce bronchodilation and protect the lung from subsequent bronchoconstriction (termed bronchoprotection). These effects may be due in part to dynamic stretch on airways produced by cyclical expansion of airway diameter. However, airways also lengthen cyclically during breathing. The effects of cyclical airway elongation on evoked bronchoconstriction have not been examined. This study recorded evoked contractions of pig bronchial segments 1) at different airway lengths, 2) after a period of cyclical lengthening in relaxed airways, and 3) during cyclical lengthening in pretoned airways. Airway segments were mounted in organ baths and bathed in Krebs solution luminally and on the adventitia. Airways were cyclically lengthened by 5-30% of their deflated length at 0.5-2 Hz for 5 min. Contractions were evoked by electrical field stimulation or carbachol and were recorded under isovolumic conditions. Under static conditions, there was a blunt relationship between length and response to electrical field stimulation. After a period of airway length cycling, electrical field stimulation-induced contractions were increased. In airways pretoned with carbachol, cyclical lengthening produced a transient bronchodilation and a sustained increase in contraction. Contractile responses were not blocked by indomethacin. The results show that isolated airways respond actively to dynamic changes in length. Our results indicate that cyclical lengthening of airways could contribute to lung function in vivo but does not appear to account for the phenomenon of bronchoprotection.
