Biomedical subjects

J Froelich

Publications and source records attributed to J Froelich.

4 recordsLinked to original sources

PubMed1992

Injection characteristics and downstream contrast material distribution of flush aortography catheters: in vitro study.

Performance of 11 commercially available 4- and 5-F aortic flush catheters was evaluated with respect to the extent of upstream injection, catheter motion, and downstream homogeneity of a 10-, 15-, and 20-mL/sec bolus of 76% meglumine sodium diatrizoate at room temperature. Tests were made in a pulsatile aortic flow model containing circulating fluid isoviscous to blood. The injection process was recorded on videotape. Homogeneity of the contrast material bolus was determined spectrophotometrically from samples collected from the center and each of the four quadrants of the vessel lumen. Upstream contrast material injection between 1.5 and 7 cm in length emerged from all catheters; it was lowest with one of the "tennis racket" designs from one and a new spiral end-loop design (Halo) from another manufacturer. All catheters, except the most rigid and largest-caliber catheter (5.8 F) showed considerable shaft motion at the higher injection rates. Downstream contrast material mixing homogeneity was always best at the highest injection rate but altogether was better for the Halo catheter than for any other catheter tested. It is concluded that all tested 4- and 5-F aortic flush catheters show some undesirable features, but certain design modifications improve performance and comparative testing is helpful to distinguish such features.

Aortography↗

PubMed1987

Utility of lymphoscintigraphy in directing surgical therapy for melanomas of the head, neck, and upper thorax.

Lymphoscintigraphy with technetium99m antimony sulfur colloid or technetium99m human serum albumin helped direct the surgical management of 24 patients who had melanomas of the head, neck, and upper thorax. Eighteen (75%) patients had documented lymphatic flow to other than a single adjacent predictable lymph nodal group. Nineteen patients underwent lymphadenectomy. Availability of the scan altered surgical management in nine patients (47%) who required resection of nodes in addition to resection of adjacent nodes. The discovery of metastatic disease in one patient was clearly attributable to lymphoscintigraphy. This demonstrates the unpredictable lymphatic anatomy of this region and suggests that preoperative lymphoscintigraphy may be useful in directing the surgical management of cutaneous melanomas in which lymph node dissection is planned.

Adult↗

PubMed1986

Optimisation of indices of external pneumatic compression for prophylaxis against deep vein thrombosis: radionuclide gated imaging studies.

The amount and rate of blood expelled with different modes of intermittent external pneumatic compression applied to the lower leg were studied on a regional basis in a series of experiments on healthy human volunteers. Radionuclide imaging of the labelled blood pool, with acquisition of counts synchronised to the pressurisation cycle, provided data on regional blood volumes in the leg in relation to time. To determine the changes in blood volume of the lower leg resulting from external pneumatic compression labelled red blood cell counts were determined during 10 different types of compression cycle. Since venous stasis is considered to be a major cause of venous thrombosis the red blood cell counts were used to calculate regional values of the fraction of blood ejected as well as comparative indices proportional to regional flow rate, regional velocity, and regional wall shear stress. All these indices should be maximised for optimal prophylaxis against deep vein thrombosis. The four compartment cuff in each compression mode applied a mean pressure of 45 mm Hg, but different combinations of values were used for intercompartmental pressure gradation (delta p) and for intercompartmental time sequencing to the onset of compression (delta t). Uniform compression (delta p = 0; delta t = 0) was substantially inferior to cycles with gradation and sequencing. The optimal values of delta p were in the range 5-10 mm Hg and of delta t in the range 0-0.5 seconds.

Adolescent↗

PubMedDate not supplied

SAR reduced pulse sequences.

Three techniques were considered for reducing the RF (radiofrequency) power deposition in the body while maintaining scan time efficiency: reducing the RF peak amplitude while increasing the pulse width, substituting gradient echoes for spin echoes, and reducing the flip angle of the phase reversal pulse. The use of gradient echoes was found to be the most efficient means to reduce the power delivered to the patient and to obtain rapid data acquisition. The effect upon SAR (specific absorption rate) and SNR (signal-to-noise ratio) was demonstrated on a phantom when the phase reversal pulse was reduced from the standard 180 degrees to 90 degrees. Data in the body indicated a fairly constant SNR down to a refocusing flip angle between 110 degrees and 135 degrees. An initial clinical evaluation was performed at three institutions using the method of reducing the flip angle of the phase reversal pulse. The scan with theta = 120 degrees was rated by readers in a blinded study as having acceptable diagnostic image quality while the 135 degrees scan had comparable image quality to a conventional 90 degrees - 180 degrees pulse sequence. The use of reduced phase reversal pulses was seen as an efficient protocol to obtain T1-weighted images at rapid data rates while reducing the power delivered to the body by about 40%.

Humans↗