[Partial k-space sampling with zero filling used with phase-contrast flow measurements: in vivo and in vitro validation]. / Partielle k-Raum-Auslesung mit Null-Interpolation bei Phasenkontrast-Flussmessungen: In-vivo- und In-vitro-Validierung.

PURPOSE: To validate the technique of partial k-space sampling and zero filling with phase-contrast flow measurements as compared to measurements with full k-space sampling. MATERIALS AND METHODS: In vitro: A laminar flow phantom was utilized to evaluate the effect of partial k-space sampling on the accuracy, precision and signal-to-noise ratio of phase-contrast flow measurements. In vivo: The effect of partial k-space sampling on the quantification of cardiac output (n = 40 patients) and the duration of the scan were evaluated in the ascending aorta (n = 37) and pulmonary trunk (n = 34) in a prospective study. RESULTS: Partial k-space sampling resulted in an increase in the SNR by 2 % in vitro. The precision was altered by less than 1 %. Flow volumes were systematically overestimated by 3.5 %. No significant differences were found in the in vivo measurements of cardiac output. The scan duration was reduced by 34 % by utilizing partial k-space sampling. CONCLUSION: Partial k-space sampling can be used to reduce scan time without a significant decrease in the accuracy or precision of phase-contrast flow measurements in large arteries.

[Conventional and virtual simulation in retrobulbar irradiation]. / Konventionelle und virtuelle Simulation bei der Retrobulbärbestrahlung.

BACKGROUND: Radiotherapy is commonly used in Grave's ophthalmopathy. The target volume encompasses the ocular muscles and the orbital tissue. The result of conventional simulation can be examined by means of CT simulation. PATIENTS AND METHODS: Twenty-five planning CTs with Grave's ophthalmopathy were studied. The conventional simulation of 4 x 4 cm2 lateral portals confined anteriorly by the fleshy canthus was performed on a CT-simulator using the observer's eye view (OEV) and digitally reconstructed radiographs (DRR). The coverage of the target volume and sparing of the eye lenses were studied on axial CT slices and multiplanar reconstructions (MPR). The distances between the apex of the orbita and cornea, fleshy canthus, and bony canthus were measured as well as the distance between cornea and posterior face of the lens. RESULTS: The pituitary gland and the ocular lenses were spared in each case (25/25). The orbita was entirely covered in 24 cases (96%). However, anterior parts of the external eye muscles were not completely encompassed in 7 cases (28%). The distance from the apex of the orbita to the cornea was 54.6 mm (53.3 to 55.8 mm, 95% confidence interval), to the fleshy canthus 40.3 mm (39.4 to 41.2 mm), and to the bony canthus 31.4 mm (30.2 to 32.5 mm). The distance between cornea and posterior face of the lens was 8.3 mm (7.9 to 8.7 mm). The distance between cornea and canthus differed significantly from normal eyes while the distance between cornea and posterior face of the lens was very similar to normal eyes. CONCLUSIONS: Conventional simulation of orbital irradiation with lateral fields confined anteriorly by the fleshy canthus ensures protection of the ocular lenses and the pituitary gland. However, anterior parts of the eye muscles may occasionally not completely be covered. The fleshy canthus and the cornea are more reliable landmarks as compared to the bony canthus.

The role of CT simulation in whole-brain irradiation.

PURPOSE: Evidence is growing that incorrect field-shaping is a major cause of treatment failure in whole-brain irradiation (WBI). To evaluate the potential benefits of CT simulation in WBI we compared field-shaping based on 3D CT simulation to conventional 2D simulation. METHODS: CT head scans were obtained from 20 patients. Conventional 2D planning was imitated by drawing the block contours on digitally reconstructed radiographs (DRR) by four radiotherapists. Critical parts of the target and the eye lenses were subsequently marked and planning was repeated using 3D information ("3D planning"). The results of both methods were compared by evaluation of the minimal distance from the field edge according to each site. RESULTS: In conventional planning using DRR, major geographic mismatches (< -3 mm) occurred in the subfrontal region and both eye lenses with 1% each location. Minor mismatches (-3 to 0 mm) predominantly occurred in the contralateral lens (21%), ipsilateral lens (10%), and subfrontal region (9%). Close margins (0-5 mm) were most frequently noted at the contralateral lens (49%), ipsilateral lens (35 %), and the subfrontal region (28%). When 3D planning was used, mismatches were not found. However, close margins were inevitable at the ipsilateral lens (5%), subfrontal region (30%), and contralateral lens (70%). CONCLUSIONS: CT simulation in WBI is significantly superior to conventional simulation with respect to complete coverage of the target volume and protection of the eye lenses. The narrow passage between the ocular lenses and lamina cribrosa represents a serious limitation. These patients are safely identified with CT simulation and can be referred for modified irradiation techniques.