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Biomedical subjects

M P Hayball

Publications and source records attributed to M P Hayball.

10 recordsLinked to original sources
PubMed2000

Assessment of quantitative computed tomographic cerebral perfusion imaging with H2(15)O positron emission tomography.

Assessment of quantitative cerebral blood flow on a conventional fast CT machine without the use of specialized equipment may be valuable in the investigation of acute stroke and head injury. We aimed to compare a single slice CT perfusion sequence with H2(15)O positron emission tomography using the sagittal sinus as an input function, a method that avoids unnecessary orbital irradiation. Eight patients were studied, two patients with gliomas, and six with arteriovenous malformations. The dynamic CT perfusion sequence was performed by acquiring the same 10 mm slice 10 times over 30 sec during a 50 ml bolus of intravenous contrast medium given at a rate of 7.5 ml sec-1 using a power injector. The CT perfusion studies were completed without complication. Co-registration was sub-optimal in one patient. Overall the correlation between the two methodologies was encouraging with an average r2 value of 0.524 for individual analyses. When two patients with high flow arteriovenous malformations were excluded the average r2 value increased to 0.640. The results of this CT perfusion methodology are encouraging. Having shown its feasibility, further studies in conditions with lower rates of cerebral blood flow are warranted.

Adult↗
PubMed2000

Impact of motion artefact on the measurement of coronary calcium score.

Reports have shown that total coronary calcium (CC) measured by electron beam CT (EBCT) correlates well with atheroma extent, and this in turn is a reliable indicator of risk for future ischaemic events. Although total CC may be measured using a conventional CT scanner, image quality is degraded by cardiac motion artefact. Errors in CC measurement owing to slice misregistration between adjacent breath-holds affect both conventional CT and EBCT. The latest generation conventional CT scanners have acquisition times of 500 ms or shorter, and, when combined with ECG triggering, quantitative CC measurement without reliance upon EBCT becomes a real possibility. We investigated the effect of motion on the measured calcium score using a moving phantom. Our results show that use of ECG triggering with conventional CT improves reproducibility of Agatston calcium score measurement. Increasing motion time during image acquisition results in an apparent increase in the Agatston CC score. Alternative measures of the amount of CC may be less susceptible to motion-induced bias, but have a similar reproducibility.

Algorithms↗
PubMed1998

In vivo assessment of neovascularization of liver metastases using perfusion CT.

Neovascularization of tumours produces a high microvessel density. Although diagnostic imaging is unable to visualize microvessels directly, it is possible to demonstrate associated changes in tissue perfusion. The aim of this study was to use the quantitative functional information and high spatial resolution of perfusion computed tomography to study neovascularization of hepatic metastases. Perfusion CT was performed in 13 patients with hepatic metastases from various primary tumours. Arterial perfusion was measured in the metastasis; both arterial and portal perfusion were measured in a small rim of liver tissue immediately adjacent to the metastasis. Perfusion measurements were correlated against survival of the patient in nine cases. Arterial perfusion was increased above normal values, both in the metastasis (median: 0.62 ml min-1 ml-1; range: 0.26-3.05 ml min-1 ml-1) and in the adjacent liver (median: 0.51 ml min-1 ml-1; range: 0.14-1.60 ml min-1 ml-1). Portal perfusion of adjacent liver was highly variable (median: 0.30 ml min-1 ml-1; range: 0.05-1.85 ml min-1 ml-1). Arterial perfusion was positively correlated with portal perfusion within liver tissue adjacent to metastases (p < 0.05, r = 0.58), a reversal of the normal situation. Survival of the patient correlated with arterial perfusion within the metastasis (p < 0.05, r = 0.69) but more closely with arterial perfusion in the adjacent liver (p < 0.02, r = 0.78). In conclusion, alterations in perfusion within metastases and adjacent liver are in accordance with the histological features of neovascularization. Perfusion CT offers a method for studying neovascularization in the living patient and offers prognostic information.

Carcinoma↗
PubMed1995

Non-invasive measurement of azygos venous blood flow using magnetic resonance.

Monitoring treatment efficacy in patients with portal venous hypertension has been limited by the difficulty of direct or indirect assessment of portal vein pressure. The majority of currently available haemodynamic tests, such as hepatic vein wedge pressure or azygos vein flow measurement by thermodilution catheter, are invasive which has restricted their application. We describe a non-invasive cine phase contrast magnetic resonance technique for quantitative measurements of bulk volume flow and for demonstrating flow changes during the cardiac cycle in the azygos vein. The technique was used to analyse the azygos vein flow in seven adult volunteers and five patients with biopsy-confirmed chronic liver disease, portal hypertension and endoscopically proven oesophageal varices. In the volunteers the mean volume flow rates varied between 81 and 241 ml/min with a mean for the group of 171 ml/min. The patients had a significantly higher mean volume flow rate of 628 ml/min (p < 0.01), with a range of 339 to 945 ml/min. These preliminary results suggest that cine phase contrast magnetic resonance angiography is a practical non-invasive method for measuring absolute azygos vein flow, and may provide a non-invasive method of monitoring portal hypertension.

Adult↗
PubMed1995

Transient splenic inhomogeneity with contrast-enhanced CT: mechanism and effect of liver disease.

PURPOSE: To use computed tomography (CT) and functional imaging to characterize the physiologic processes that result in transient splenic inhomogeneity during contrast material enhancement and determine their value in detection of diffuse liver disease. MATERIALS AND METHODS: CT scan data from nine control patients and 13 patients with diffuse liver disease were used to create functional images that displayed splenic perfusion and time to peak enhancement. A pixel-by-pixel analysis was used to create these images. RESULTS: Areas of early enhancement demonstrated higher perfusion and vice versa. In patients with liver disease, splenic perfusion values fell from 1.44 to 1.22 mL/min/mL in the areas that showed early enhancement and 1.24 to 0.89 mL/min/mL in the areas that showed late enhancement. As splenic perfusion values fell, the size of the regions that showed late enhancement increased. CONCLUSION: The combination of functional images and CT data has clarified the mechanism by which transient splenic inhomogeneity occurs and is of potential value in the detection of diffuse liver disease.

Adult↗
PubMed1995

Measurement of human pancreatic perfusion using dynamic computed tomography with perfusion imaging.

Absolute quantification of pancreatic perfusion in man has been extremely difficult to date. This paper describes a relatively simple application of dynamic computed tomography to provide perfusion imaging of the human pancreas. Values for perfusion in eight normal pancreases ranged between 1.25 and 1.66 ml min-1 ml-1 (mean: 1.52 ml min-1 ml-1). Increased perfusion values were present in a patient with an islet cell tumour (overall perfusion 2.11 ml min-1 ml-1) and a patient with Wilson's disease (3.43 ml min-1 ml-1). Pancreatic perfusion was reduced in a patient with diabetes (0.60 ml min-1 ml-1) and in a failing pancreatic transplant (0.97 ml min-1 ml-1). The combination of functional information and good spatial detail afforded by computed tomography (CT) perfusion imaging means the technique is well suited for the evaluation of the human pancreas. It is currently the only technique which allows non-invasive absolute quantification of pancreatic perfusion.

Adenoma, Islet Cell↗
PubMed1994

Functional imaging of changes in human intrarenal perfusion using quantitative dynamic computed tomography.

RATIONALE AND OBJECTIVES: Quantitative dynamic computed tomography was used with perfusion imaging to characterize intrarenal variations in perfusion in normal and abnormal human kidneys. METHODS: Perfusion images were obtained from 14 normal and four abnormal kidneys, comprising a renal tumor, an infarcted renal allograft, and two kidneys in a patient with cyclosporin toxicity. RESULTS: Images demonstrating quantifiable intrarenal variations in perfusion were consistently obtained. Normal cortical and medullary perfusion were 4.7 mL/min/mL and 1.1 mL/min/mL, respectively, consistent with accepted normal ranges. The changes in the abnormal kidneys corresponded with known pathophysiology. CONCLUSION: Computed tomography perfusion imaging creates quantifiable images of renal perfusion with a spatial resolution currently higher than any other functional imaging technique. It offers the opportunity to characterize renal diseases by their relative effects on cortical and medullary perfusion.

Adult↗
PubMed1993

Functional images of hepatic perfusion obtained with dynamic CT.

A dynamic computed tomographic (CT) technique for separate quantification of arterial and portal components of liver perfusion with functional imaging was developed and used to study 24 livers. A single-location dynamic sequence was performed after intravenous administration of a 50-mL bolus of contrast medium. The time to maximum splenic enhancement was used to differentiate arterial and portal phases, and the maximal slopes of the liver time-density curve in each phase were used to calculate both arterial and portal perfusion. The arterial/total perfusion ratio was also calculated. The values of these parameters for individual pixels were used to create functional images. Arterial perfusion was increased in patients with metastases and cirrhosis. Portal perfusion was reduced in patients with cirrhosis. Functional images were successfully created in all but one case. The technique enables quantification and functional mapping of several perfusion parameters with a spatial resolution greater than that achieved with other imaging techniques.

Aged↗
PubMed1991

Comparative performance in vitro and in vivo of Lunar DPX and Hologic QDR-1000 dual energy X-ray absorptiometers.

The measured absolute bone mineral density values of spine and femur and their precision were compared on two dual energy X-ray absorptiometers, the Lunar DPX and the Hologic QDR-1000. There were systematic differences between the two systems, the Lunar DPX always giving a higher bone density value. The ratio of the mean Lunar DPX/Hologic QDR-1000 bone density measurements obtained in vivo was 1.13 g/cm2 for spine (L2-L4) and 1.20-1.43 g/cm2 for femur measurements. For both systems, short- and long-term precision (coefficient of variation) was below 0.5% for spine in vitro measurements and below 1.5% for neck of femur in vitro measurements. Precision of in vivo measurements was less good, especially for femur measurements. The coefficient of variation of spine measurements was dependent on bone density and deteriorated with decreased bone mineral density and increased body thickness.

Absorptiometry, Photon↗