Biomedical subjects

O Pahlm

Publications and source records attributed to O Pahlm.

75 records · Page 5Linked to original sources

PubMedDate not supplied

Clinical implication of down-scatter in attenuation-corrected myocardial SPECT.

BACKGROUND: Interpretation of myocardial perfusion single photon emission computed tomography (SPECT) studies is hampered by attenuation artifacts. Attenuation correction methods with simultaneous emission and transmission are now commercially available. However, it has been observed in clinical practice that attenuation correction without down-scatter correction in a 1-day rest/stress myocardial perfusion protocol may lead to serious interpretation errors. Therefore the aim of this study was to study errors resulting from down-scatter under realistic conditions, thus providing a background for the assessment of further corrections. METHODS AND RESULTS: Forty-six patients underwent myocardial perfusion scintigraphy in a 1-day technetium 99m-tetrofosmin rest-stress SPECT protocol, with a moving 153Gd line-source device for attenuation correction without down-scatter correction. Short-axis slices were quantified as inferior/anterior, septal/lateral, and apical/remainder count ratios. The changes at rest (350 MBq) and exercise (900 MBq) induced by attenuation correction were studied. Attenuation correction gave differences in apparent perfusion between rest and exercise not seen before correction. The gender differences in inferior-anterior ratio were greatly reduced after correction at rest but remained at exercise. A torso phantom study indicated that these results were due to under-correction at exercise because of down-scatter. CONCLUSIONS: Down-scatter results in an underestimation of attenuation in simultaneous emission and transmission, if not accurately accounted for. Particularly, a high-dose study compared with a low-dose study, as in the 1-day protocol, might cause serious interpretation errors.

Artifacts↗

PubMedDate not supplied

Quantification of vestibular dysrhythmia.

Quantification of dysrhythmia in a nystagmus response has hitherto not been seriously attempted, possibly because the nystagmus response does not easily lend itself to description in mathematical or physical terms. Ideally the nystagmus response consists of a sequence of triangles. Each such triangle is determined by four qualities, i.e. the velocities and the durations of the fast and slow components. Thus, without serious loss of information it is possible to represent a nystagmus reaction by four sequences of values, one for each of the four above mentioned qualities. From each such sequence we have extracted relevant information and presented it in graphical form. It may be assumed that each of the four nystagmus qualitiees reflects the activity within separate 'neuronal systems'. Each of these four systems is then informed upon by three parameters for each nystagmus quality, i.e. by its mean, by its variation coefficient and by its sequential variation coefficient. It is claimed that these three diagrams contain nystagmus information not earlier considered.

Adult↗

PubMedDate not supplied

The dysrhythmia and the exponential constants of the postrotatory nystagmus qualities.

In 5 healthy individuals the postrotatory, exponential constants were estimated for each of the four nystagmus qualities, viz. the velocities and durations of fast and slow components. The residual spread (Sr) of each quality in a semilogarithmic plot was also determined. The value of the constant for postrotatory decay indicated a decrease of the velocity and an increase for the duration of the slow component, both with a significant difference between individuals, while for the corresponding values of the fast components no systematic change in the postrotatory reactions was indicated, nor any difference between individuals. The constant that corresponds to the value at maximum stimulus showed differences between individuals for each of the four nystagmus qualities, while Sr presented differences between individuals only for the two slow phase qualities. This technique to describe postrotatory nystagmus reactions by the two exponential constants for each of the four nystagmus qualities together with the residual spread for each of the qualities is intended for future 'on-line' nystagmus analysis.

Eye Movements↗