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M R Rees

Publications and source records attributed to M R Rees.

At least 55 records · Page 3Linked to original sources
PubMed1990

Thermal characteristics of sapphire contact probe delivery systems for laser angioplasty.

Contact probes made from synthetic sapphire crystal, designed for general laser surgery, are currently being evaluated for use in laser angioplasty. Their mode of action and safety in the context of arterial recanalisation is unknown, particularly with respect to the degree of probe and catheter heating. Infrared thermal imaging was used to investigate the surface temperature rise of various rounded sapphire probes during emission of continuous wave Nd-YAG (1,064 nm) laser energy. Catheter safety was addressed by analyzing the temperature of the metal interface between the optical fiber and sapphire, as well as the catheter proximal to this junction. Transmission of Nd-YAG energy through each probe was also measured. Five rounded probes of 1.8-3.0 mm diameter (three supplied by Surgical Laser Technologies [SLT], two by Living Technology [LT]), along with their respective optical catheters, were compared. There was a large temperature gradient between the front and rim of the probes. The maximum surface temperature rise of the sapphire (at 20 W, 5-second exposure) was 314-339 degrees C (SLT) and 90-108 degrees C (LT) [P less than 0.001, 3-way ANOVA]. The reason for this difference may be related to "crazing" of the front surface of the SLT sapphires. At all energy levels sapphire temperatures were considerably lower than attained by metal laser thermal angioplasty probes. Forward transmission was slightly higher in the SLT probes (75-85%) than the LT sapphires (54-69%). With fiber perfusion at 2 ml/minute, a minor degree of heating of the metal sapphire holders was recorded (maximum rise 35 degrees C), but heating of the catheter proximal to this was negligible. Therefore, it would appear that the risk of tip detachment or arterial injury due to heating of the connecting metal interface is extremely low. Without perfusion, however, there was a greater degree of interface heating in the LT delivery system suggestive of more laser backscattering by these sapphires compared with the SLT probes [P less than 0.001, one-way ANOVA]. The SLT system is, therefore, potentially safer in this respect. These results suggest that some degree of surface heating of contact probes due to energy absorption within the sapphire does occur, but is localised to the front of the probe. This effect may contribute to the process of arterial recanalisation with this device. However, variation in the thermal and optical properties of sapphires from different sources has been demonstrated. The influence of these properties on plaque ablation, and ultimately the clinical performance of different contact probe systems, requires further investigation.

Humans↗
PubMed1990

Aneurysm formation after dynamic catheter assisted balloon angioplasty.

A male patient underwent recanalisation of a symptomatic popliteal artery occlusion using a dynamic angioplasty catheter, followed by balloon dilatation. A small subintimal dissection lead to an acute reocclusion. Repeat balloon angioplasty reopened the occlusion but was complicated by a distal embolus which was successfully treated by thrombolytic therapy followed by oral anticoagulation. Angiography 9 months later, demonstrated an aneurysm at the site of initial dissection. The artery remained patent and the patient free of claudication. A causal relationship between dynamic angioplasty and subsequent aneurysm formation is suggested and the possible predisposing factors discussed.

Aneurysm↗
PubMed1990

Experimental analysis of sapphire contact probes for Nd-YAG laser angioplasty.

Laser angioplasty may offer percutaneous recanalization of occluded vessels where conventional guidewire and balloon techniques fail. Metal laser thermal angioplasty probes may, however, cause excessive thermal damage due to high tip temperatures (greater than 400.C). Therefore, contact probes made from artificial sapphire crystal designed for general laser surgery are currently being evaluated for use in laser angioplasty with continuous wave Nd-YAG energy. The sapphire modifies the laser energy in various ways, and this paper examines the physical characteristics of five types of rounded sapphire probe (SMTR, MTR, MTRL, OS, LT) and how these properties are affected by clinical usage. The laser beam profile emitted by these probes demonstrates a focal spot 1-2 mm in front of the tip. However, the forward transmission of Nd-YAG energy through the sapphires varied (SMTR, 85%; MTR, 83%; MTRL, 75%; OS, 54%; LT, 69%). Probe heating occurs owing to energy absorption within the sapphire. The surface temperature of the sapphires was measured in air by infrared thermography and the hottest region within the probes localized by an isothermographic technique. At energy settings used clinically (20 J, 10 watts for 2 s) the SMTR, MTR, and MTRL probes exhibited higher temperature rises (94-112.C) than the OS and LT probes (30.C), and heating was localized to the front surface of the former probes. Peak sapphire temperatures remained lower than those of metal probes even at higher energies. After clinical use, the MTR probe demonstrated reduced transmission, beam defocusing, and increased heating, due to surface pitting. Thus, recanalization with sapphire probes occurs by a combination of photothermal and contact thermal effects that are localized to the probe tip and may reduce the degree of thermal injury associated with metal probes. Understanding these basic properties is important to the application and development of contact probes for laser recanalization.

Aluminum↗
PubMed1990

Experimental and clinical percutaneous angioscopy experience with dynamic angioplasty.

The authors have used ultrathin angioscopes with high optical resolution to assess the effects of dynamic angioplasty in vitro and in vivo. Experimentally, angioscopy was used to study the effects of the 5F "Kensey" catheter in "normal" porcine coronary arteries (NPCA) and postmortem human coronary arteries (PMHCA). In NPCA, the catheter keeps a coaxial position. Intimal flaps (IFs) were seen in 21/23 NPCAs. They occurred with all cam rotation speeds and were usually single and small (less than 25% of lumen). Perforations in patent arteries were rare (1/23). However, when the catheter was forced against the wall by passing through a narrowing of 5F diameter (made by a band ligature), perforations were more common at higher cam speeds. The epicardium remained intact in two thirds of perforations. Angioscopy visualized perforations in only 10% of cases (1/10), the common sign being that of large and multiple intimal flaps, which were often obstructive (5/10). In PMHCAs, angioscopy was more sensitive than angiography in detecting atheromatous lesions. The authors were able to give a better assessment of the effect of dynamic angioplasty on treated lesions, including the demonstration of intimal flaps that were not visible on angiography. In vivo, they have performed percutaneous angioscopy before and after dynamic angioplasty using 8 French Kensey catheters. Angioscopy revealed features that were not shown angiographically.

Angioplasty, Balloon↗
PubMed1989

Percutaneous video angioscopy in peripheral vascular disease.

Percutaneous video angioscopy was performed using high resolution thin angioscopes in 12 peripheral arteries in 10 patients with peripheral vascular disease, to study the intraluminal appearance before and after dynamic, laser and conventional balloon angioplasty. Clear blood free views of the whole length of artery instrumented were obtained in 10 arteries with the remaining two arteries being partially visualised. The angioscopic appearances were compared to angiography. Clinically significant findings were detected in all the arteries by angioscopy that were not found by angiography. These included thrombus in the artery and vascular sheath, intimal flaps and fractured atheroma. The angioscopic findings helped to assess the effects of angioplasty in different types of occlusion. The findings demonstrate the potential of percutaneous angioscopy as an aid to percutaneous angioplasty as well as being a powerful diagnostic procedure.

Aged↗
PubMed1989

Radiographic features and prognosis in bronchioloalveolar carcinoma; a local experience.

The prognosis of 20 patients with histologically proven bronchioloalveolar carcinoma was assessed in the light of their radiographic features and symptoms at presentation. Radiographically, half the patients were classified as having focal disease of which 60% were focal consolidation. Other focal presentations were, a mass lesion in three cases and a single 3 cm nodule in one case. Those with diffuse disease presented with either coarse widespread nodules or diffuse alveolar opacification with or without a focal area of consolidation. All patients were symptomatic at presentation but the severity of the symptoms bore no relation to the radiological findings. Seven cases with focal disease underwent thoracotomy, five of which had evidence of hilar and mediastinal lymph node involvement. They included a case presenting with a nodule, two with a mass and four with focal consolidation. The survival following surgery was generally better with those with a mass or nodule but one case with focal consolidation remains alive 10.5 years following surgery compared with the longest survivor of 4.5 years with a mass. Both these relatively long-term survivors had no histological evidence of hilar or mediastinal lymph node involvement compared with the other surgical cases. The median survival in cases without surgery was one month. The prognosis was better in patients with focal disease where surgery was performed and we feel that a local area of consolidation should be treated as focal disease and surgical resection considered for these patients.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1988

Assessment of global and regional left ventricular function in ischemic heart disease using ultrafast computed tomography.

Contrast-enhanced ultrafast computed tomography (CT) of the left ventricle was done in the long axis and short axis within one day of cardiac catheterization in 14 males with ischemic heart disease and a mean age of 58 years. Imaging was R wave-triggered at 58-msec intervals (13/level). Left ventriculography was performed in 30 degrees right anterior oblique (RAO) and 60 degrees left anterior oblique (LAO) caudal 12 degrees. CT left ventricular ejection fraction was measured using a modified Simpson's reconstruction of end-systolic and end-diastolic slices. Catheterization left ventricular ejection fraction was measured by area-length method. Six left ventricular segments (septal, apex, anterior, lateral, inferior, and posterior) were scored by different paired observers as follows: dyskinesis (-1), akinesis (0), moderate-severe hypokinesis (1), mild hypokinesis (2), and normal (3). Correlations of left ventricular ejection fraction for catheterization vs. long-axis CT and short-axis CT were r = .83 and r = .86, respectively. Seven of eight patients with transmural myocardial infarction were identified on CT by akinetic/dyskinetic segments. Eighty-four segments were scored. There was agreement (normal vs. abnormal) in 76 (90%). CT detected 47 normal segments vs. 51 by catheterization (92%), 11 akinetic/dyskinetic segments (92%), and 14 hypokinetic segments vs. 21 (67%). Wall motion scores between CT and catheterization differed by greater than 1 in 6 of 84 segments (7%). Therefore, ultrafast CT can accurately assess global and regional left ventricular function.

Cardiac Catheterization↗
PubMed1988

Preliminary experience in the use of ultrafast computed tomography to diagnose aortic valve stenosis.

Eight patients, mean age 72 years, with aortic valve stenosis were studied by ultrafast CT 1 day after cardiac catheterization. After injection of radiographic contrast material through a peripheral vein, two contiguous eight-level R wave-triggered cine mode scans in the short axis were acquired, starting above the aortic valve and continuing through the apex of the left ventricle. Seven of eight patients, all with calcified aortic valves, had a detectable central orifice. Catheterization-derived aortic valve areas were within 0.25 cm2 of the CT valve areas in six of seven. LV mass was measured by ultrafast CT in the eight patients with aortic valve stenosis (121.6 +/- 18.2 gm/m2) and was found to be significantly higher (p less than 0.0001) than that in a group of eight subjects with normal LV function, no history of hypertension, and normal ECGs (73.0 +/- 13.1 gm/m2). It is concluded that in selected cases ultrafast CT can contribute to the assessment of severity of calcific aortic stenosis by measurement of LV mass and valve area.

Aged↗
PubMed1988

Determinants of left ventricular ejection fraction by ultrafast computed tomography.

Twenty-seven patients had left ventricular ejection fraction (LVEF) measured by catheterization, single-plane angiography, and ultrafast computed tomography (cine CT). Twelve patients (mean age sixty-two years) had LVEF measured by use of the cine CT long-axis view LAV), and 15 patients (mean age fifty-eight years) had LVEF measured by use of the cine CT transaxial view (TAV). Cine CT LVEF was measured by means of two methods of edge detection (M1 and M2). A significant correlation was found between single-plane angiography and cine CT LAV LVEF (M1, r = .96; M2, r = .93). A lesser correlation was found for catheterization vs TAV cine CT LVEF (M1, r = .77; M2, r = .81). There was no significant difference between the two methods of edge detection for determining LVEF (M1 vs M2: LAV, r = .98; TAV, r = .94); however, there was significant variability in cavity volumes. Therefore, the LAV is superior to the TAV for measurement of LVEF by cine CT; however, different methods of edge detection, though affecting volumes, may not affect LVEF.

Cardiac Catheterization↗
PubMed1987

Demonstration of mitral and aortic valves by ultrafast computed tomography.

Contrast medium-enhanced ultrafast computed tomography has sufficient spatial and temporal resolution to permit imaging of the mitral and aortic valves. The conventional transaxial planar scan projection is not adequate for this purpose. This communication describes the planar configurations and technique required to image the mitral and aortic valves by ultrafast computed tomography.

Aortic Valve↗
PubMed1986

Quantitation of shunting at the atrial level using rapid acquisition computed tomography with comparison with cardiac catheterization.

Contrast-enhanced rapid acquisition computed tomography was employed to quantitate intracardiac shunts in two adult patients. Contrast medium was injected through a median antecubital vein and data were accumulated using the R wave-triggered flow mode. Time-density curves from a region of interest were generated by a gamma variate fit method and areas under the curves were calculated. Comparisons of calculated left to right shunts (Cases 1 and 2) with results of computed tomography and right to left shunt (Case 2) with cardiac catheterization data resulted in close agreement. This is the first report of quantitation of intracardiac shunts at the atrial level in humans by rapid acquisition computed tomography.

Adult↗
PubMed1986

Heart evaluation by cine CT: use of two new oblique views.

Two new oblique views on cine computed tomography for examination of the left ventricle of the heart are described. A short-axis view sections the left ventricle transversely, demonstrating all the ventricular walls; a long-axis view sections the left ventricle longitudinally, demonstrating the mitral valve, proximal aortic root, aortic outflow tract, and ventricular apex. These views are produced by a combination of table slew and patient positioning. Reproducible short-axis views were obtained in 16 healthy volunteers and 11 patients. Long-axis views were obtained in 11 patients. Patient studies in the long-and short-axis views were compared with results from angiocardiography, with nearly identical findings.

Adult↗