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Biomedical subjects

A K Dixon

Publications and source records attributed to A K Dixon.

At least 19 recordsLinked to original sources
PubMed2006

A simple processing method allowing comparison of renal enhancing volumes derived from standard portal venous phase contrast-enhanced multidetector CT images to derive a CT estimate of differential renal function with equivalent results to nuclear medicine quantification.

As iodinated contrast medium is cleared by glomerular filtration, it should be possible to apply the same principles utilized in radionuclide studies to derive differential renal function by comparison of enhancing renal volumes derived from contrast enhanced multidetector CT (CEMDCT). Having established a technique iteratively which appeared successful, a retrospective study was performed using 25 consecutive patients with a wide range of urological conditions who had undergone both CEMDCT, including the renal area in the portal venous phase, and nuclear medicine (NM) assessment of renal function with no urological intervention between the studies. Proprietary volume software was used to quantify the volume and attenuation of each kidney, the products of which (after subtraction of soft tissue attenuation derived from a region of interest over psoas) gave right and left enhancing renal volumes. The contribution by each kidney as a percentage of total renal enhancing tissue was derived. Comparison with NM studies resulted in excellent correlation of relative renal function by CEMDCT and NM assessments having a regression of near unity and a Pearson's correlation coefficient of 0.96. Bland Altman and Passing Bablock tests confirmed good agreement between the two methods with no bias. This is a simple, practicable processing technique using standard portal venous phase CEMDCT images to quantify differential function. This technique may allow a one-stop CT assessment of both anatomy and function.

Adult↗
PubMed2005

Noradrenergic receptor mRNA expression in adult rat superficial dorsal horn and dorsal root ganglion neurons.

Noradrenaline (NAdr) has well documented analgesic actions at the level of the spinal cord. Released from bulbospinal projections onto superficial dorsal horn (SDH) neurons, NAdr modulates the excitability of these neurons through the activation of alpha1, alpha2 or beta adrenoceptors. This study utilised in situ hybridisation to determine the specific expression of adrenoceptors within adult rat lumbar SDH and dorsal root ganglion (DRG) neurons, and reports the presence of alpha1A, alpha1B, alpha2B, beta1 and beta2 adrenoceptor mRNA within SDH neurons, and the presence of alpha1A, alpha1B and alpha2C adrenoceptor mRNA within DRG neurons. The present study provides an insight into the modulation of sensory processing at the level of the spinal cord following adrenoceptor activation.

Animals↗
PubMed2005

16-Detector multislice CT in the detection of stress fractures: a comparison with skeletal scintigraphy.

AIMS: To test the hypothesis that the improved resolution afforded by 16-detector computed tomography (CT) would translate to better stress fracture detection when compared with skeletal scintigraphy. MATERIALS AND METHODS: Thirty-three cases of suspected stress fractures in 26 patients were investigated using skeletal scintigraphy and 16-detector CT performed on the same day. Planar images of the lower limbs were taken 3h post-injection of 400MBq (99m)Tc-methylene diphosphonate ((99m)Tc-MDP). (99m)Tc-MDP uptake was quantified at suspected fracture sites. CT was performed using a 16-detector multisection machine employing 0.75mm detectors and images reconstructed in 0.5mm increments. Examinations were reported independently and discordant results were compared at follow-up. RESULTS: At initial reporting scintigraphy identified fractures in 13 of the 33 cases and CT identified four of the 33. In one case, on review of the CT images, a fracture was present in the distal fibula that was not initially identified. This resulted in eight scintigraphic-positive CT-negative discordant cases. The (99m)Tc-MDP uptake was significantly lower in the discordant fracture group compared with the concordant group (p<0.01). CONCLUSIONS: Despite technological advances in CT, scintigraphy appeared to detect more stress fractures. As such, multidetector CT should not be used as a routine initial investigation in stress fracture detection. The potential use of (99m)Tc-MDP quantification at fracture sites is of interest and may be worth further investigation.

Adolescent↗
PubMed2005

Inflammatory abdominal aortic aneurysms.

BACKGROUND: Inflammatory abdominal aortic aneurysms (IAAA) are a variant of aortic aneurysm characterised by extensive peri-aneurysmal fibrosis, thickened walls and dense adhesions and represent between 3 and 10% of all abdominal aortic aneurysms (AAA). Surgery is technically challenging and is still associated with an increased morbidity and mortality. Controversy exists about aetiology and pathogenesis. METHODS: We review the literature on the current theories, the available imaging modalities and the current thinking on management of IAAA. A Medline database search was performed. Articles were cross-referenced. RESULTS AND CONCLUSIONS: Aneurysm development is multifactorial with important genetic and environmental factors. The literature supports the theory that IAAA arise from the same antigenic stimulus that is responsible for the non-IAAA, representing one extreme of an inflammatory spectrum. The results after open repair have improved and there is now little difference in the mortality between non-IAAA and IAAA repair. However, there is likely to be a role for endovascular stenting in IAAA management and this requires further study. It is clear that closer follow-up of patients after IAAA repair with either technique is necessary to monitor the inflammatory process. No evidence-based follow-up protocol exists but three to six-monthly monitoring of renal function and erythrocyte sedimentation rate (ESR) for 24 months post-repair would seem a reasonable regime.

Aortic Aneurysm, Abdominal↗
PubMed2005

16 detector multislice CT versus skeletal scintigraphy in the diagnosis of wrist fractures: value of quantification of 99Tcm-MDP uptake.

To compare the measured uptake of 99Tcm-methylene diphosphonate (99Tcm-MDP) in those scaphoid fractures seen on both 16 detector multislice CT and scintigraphy, with those seen only on scintigraphy. Over a 12 month period a total of 51 patients with suspected fracture underwent both conventional 99Tcm-MDP scintigraphy and 16 detector multislice CT on the same day. The 99Tcm-MDP uptake was then quantified in patients with identified fracture. This was measured by placing a region of interest (ROI) over the fracture site and the mean and maximum number of counts were compared with those in a similar size ROI placed over background bone activity. A total of 23 fractures were identified on scintigraphy of which 16 were also detected on CT (concordant). In seven cases the fracture was not seen on CT, even in retrospect (discordant). In the discordant cases, follow-up radiographs and MRI (where available) also failed to demonstrate a fracture. The mean fracture count to background bone activity ratio averaged 7.7 (range 3.2-18.5) for concordant fractures and 3.8 (range 1.7-5.3) for discordant fractures (t-test p=0.04). The maximum fracture count to background bone activity ratio averaged 12.7 (range 4.3-27.7) for concordant fractures and 6.3 (range 2.6-9.5) for discordant fractures (t-test p=0.03). It is speculated whether these discordant fractures with less 99Tcm-MDP uptake may represent a less severe injury such as bone bruise.

Adolescent↗
PubMed2005

Case report: False negative 16 detector multislice CT for scaphoid fracture.

We discuss a case of a 19-year-old man with scaphoid trauma. We describe the imaging findings on three sets of radiographs, bone scintigraphy, CT and MRI. CT failed to identify a scaphoid fracture, which was present on 6 week radiographs, MRI and scintigraphy. The case illustrates that despite multidetector technology, CT still relies upon cortical and or trabecular displacement to demonstrate fractures.

Adult↗
PubMed2004

Evidence against the use of lumbar spine radiography for low back pain.

AIM: To review abnormalities reported on plain radiographic examination of the lumbar spine in patients referred with low back pain by general practitioners. Additionally, we evaluated and stratified the prevalence of these abnormalities by age. Finally, the diagnostic impact of lumbar spine radiography for the diagnosis of degenerative change, fracture, infection and possible tumour, was modelled. MATERIALS AND METHODS: A retrospective review of 2007 radiographic reports of patients referred with low back pain for lumbar spine radiography to a large radiology department was performed. The reports were classified into different diagnostic groups and subsequently stratified according to age. The potential diagnostic impact of lumbar spine radiography was modelled by using the prevalence of conditions studied as pre-test probabilities of disease. RESULTS: The prevalence of reported lumbar spine degeneration increased with age to 71% in patients aged 65-74 years. The overall prevalence of fracture, possible infection, possible tumour was low in our study population: 4, 0.8 and 0.7%, respectively. Fracture and possible infection showed no association with age. Possible tumour was only reported in patients older than 55 years of age. CONCLUSION: Although the prevalence of degenerative changes was high in older patients, the therapeutic consequences of diagnosing this abnormality are minor. The prevalence of possible serious conditions was very low in all age categories, which implies radiation exposure in many patients with no significant lesions.

Adolescent↗
PubMed2004

Extracolonic findings in patients undergoing abdomino-pelvic CT for suspected colorectal carcinoma in the frail and disabled patient.

AIM: The aims of this study were to evaluate the extracolonic findings identified in patients undergoing minimal preparation abdomino-pelvic CT in place of barium enema or colonoscopy for the detection of possible colorectal carcinoma. MATERIALS AND METHODS: The CT technique involved helical acquisition (10 mm collimation, 1.5 pitch) following 2 days of preparation with oral contrast medium only. Extracolonic findings were evaluated in the light of subsequent follow-up and accuracy. The evaluation included assessment of the potential contribution of the extracolonic finding(s) to staging the cancer in the subset of patients who had colorectal carcinoma, and to account for the patients' presenting symptoms and signs in the remaining patients. RESULTS: A total of 344 extracolonic findings were detected in 261 CT examinations, from amongst a total of 1077 cases (24%). Extracolonic findings were potentially important in staging in 32 of the 98 (33%) cases subsequently found to have colorectal cancer. There were 284 extracolonic findings amongst the 221 cases who proved not have colorectal cancer. One hundred and twenty-four (44%) of these 284 findings were actively followed up by clinicians, and 33 (12%) ultimately had a surgical intervention. Fifty-six percent (160/284) of the findings were determined to be correct (by further investigation, autopsy, and/or clinical follow-up); the remainder were incorrect or indeterminate (n = 56) or had no follow-up (n = 68). The commonest extracolonic findings were focal liver lesions (found in 42/1077, 4%) and abdominal aortic aneurysms (31/1077, 3%). Twenty-four (24/1077, 2%) previously unknown extracolonic malignancies were detected. Ten percent (106/1077) of the patients had extracolonic findings that could potentially have accounted for their presenting symptoms. CONCLUSIONS: CT has the added benefit, compared with colonoscopy and barium enema, of not just evaluating the colon but also of detecting extracolonic abnormalities. Such findings may be useful in staging the cancer, may explain the patient's presenting symptoms, and may detect other potentially serious disorders.

Aged↗
PubMed2004

P2X and P2X receptor expression in human bladder urothelium and changes in interstitial cystitis.

OBJECTIVE: To investigate whether the expression of P2X(3) receptors (implicated in the pathophysiology of pain) is altered in human bladder urothelium from patients with interstitial cystitis (IC, a major symptom of which is pain), and as P2X(2) receptors can be co-expressed with P2X(3) receptors, to assess their expression also. PATIENTS AND METHODS: Bladder tissue samples were collected from patients undergoing cystectomy or radical prostatectomy. Patients with IC were diagnosed using the international criteria. RNA protein expression levels of both receptors were evaluated using reverse transcription-polymerase chain reaction (PCR), real-time quantitative PCR and Western blot analysis. RESULTS: P2X(2) was expressed in the human urothelium, in a glycosylated form. There was less gene expression of P2X(3) in IC urothelium, whereas P2X(2) gene expression was unchanged. This contrasted with the protein expression, which was increased for both P2X(2) and P2X(3). CONCLUSION: This is the first report of the expression of the P2X(2) receptor in human bladder urothelium. There was greater protein expression of both P2X(2) and P2X(3) in IC bladder urothelium which did not directly correlate with the gene expression. Changes in expression of P2X(2) and P2X(3) receptors may contribute to the pain that patients with IC have, and might provide novel drug targets.

Blotting, Western↗
PubMed2004

16-detector multislice CT: dosimetry estimation by TLD measurement compared with Monte Carlo simulation.

Computer simulations are widely used to estimate effective doses from CT examinations. The raw data often used in their estimations were obtained some years ago and made certain assumptions regarding CT unit design. At that time multidetector CT units were unavailable. Changes in design will limit the accuracy of computer simulated dosimetry on these machines. We therefore estimated CT dose on a 16-detector unit directly using thermoluminescent dosemeters (TLDs) and an anthropomorphic phantom. We found that the dose measured directly was 18% higher than the computer simulated dosimetry, in keeping with the previously recognised underestimation by computer simulation techniques compared with TLD measurements.

Computer Simulation↗
PubMed2004

Training improves medical student performance in image interpretation.

The aim of this study was to objectively quantify the effects of radiological teaching on student performance in interpreting radiological images, and to establish whether training location affects performance. 114 clinical students were asked to anonymously interpret radiological cases before and after 26 weeks clinical training. Improvements were assessed by comparing performance on the median question in each assessment using the Kruskal-Wallis analysis. Variations according to different placements were assessed by the Mann-Whitney U-test. There was a highly significant (p<0.001) improvement in the performance of the group with training. The proportion of correct answers to the median question improved from 8% to 43%. Differences between training placements were non-significant. Our study suggests that radiology teaching significantly improves student performance. Future work should look to define the contribution of "clinical exposure" towards this improvement, as well as the various teaching methods employed.

Clinical Competence↗
PubMed2003

Serotonin receptor mRNA expression in rat dorsal root ganglion neurons.

In the present study, we have used in situ hybridization to examine the distribution of serotonin (5-HT) receptors in rat dorsal root ganglion (DRG) neurons. Within DRG neurons, mRNAs for 5-HT1B, 5-HT1D, 5-HT2A, 5-HT2B, 5-HT3B and 5-HT4 receptors were readily detected in small (<25 microm), medium (25-45 microm) and large (>45 microm) diameter neurons. In contrast mRNAs for 5-HT1A, 5-HT1E, 5-HT2C, 5-HT5A, 5-HT5B, 5-HT6 and 5-HT7 receptors were undetectable in these neurons. The present study provides an insight into the molecular profile of 5-HT receptor subtypes in neurons responsible for modulating sensory information.

Animals↗
PubMed2003

Lumbar lordosis: study of patients with and without low back pain.

We used magnetic resonance imaging (MRI) to assess lumbar lordosis in 27 patients with low back pain and 19 patients and 10 volunteers with no known back pain. Our study aimed to investigate whether lordosis changes with age and is reduced in those with low back pain. Although our results confirm known observations that lumbar lordosis is more prominent in women (P < 0.01) and those with a higher body mass index (P < 0.04), we were unable to demonstrate any significant variation in lordosis with age. Nor could we demonstrate any difference in the degree of lordosis among women with or without back pain. Men with low back pain tended to have a less prominent lordosis, but this difference did not reach statistical significance. Therefore, a 'reduced lumbar lordosis' should be regarded as a very weak clinical sign.

Adult↗
PubMed2003

Identification of MEK1 as a novel target for the treatment of neuropathic pain.

(1) In the present study we have attempted to identify changes in gene expression which are associated with neuropathic pain using subtractive suppression hybridization analysis of the lumbar spinal cord of animals suffering streptozocin induced diabetic neuropathy. (2) Using this approach, we found a significant up-regulation of several key components of the extracellular signal-regulated kinase (ERK) cascade. These findings were confirmed by Western blot analysis, which demonstrated that the levels of active ERK1 and 2 correlated with the onset of streptozocin-induced hyperalgesia. (3) Intrathecal administration of the selective MAPK/ERK-kinase (MEK) inhibitor PD 198306 dose-dependently (1-30 micro g) blocked static allodynia in both the streptozocin and the chronic constriction injury (CCI) models of neuropathic pain. (4) The antihyperalgesic effects of PD 198306, in both the streptozocin and CCI models of neuropathic pain, correlated with a reduction in the elevated levels of active ERK1 and 2 in lumbar spinal cord. (5) Intraplantar administration of PD 198306 had no effect in either model of hyperalgesia, indicating that changes in the activation of ERKs and the effect of MEK inhibition are localized to the central nervous system. (6) In summary, we have demonstrated for the first time that the development of neuropathic pain is associated with an increase in the activity of the MAPK/ERK-kinase cascade within the spinal cord and that enzymes in this pathway represent potential targets for the treatment of this condition.

Animals↗
PubMed2002

Evaluation of CT in identifying colorectal carcinoma in the frail and disabled patient.

Frail and physically or mentally disabled patients frequently have difficulty in tolerating formal colonic investigations. The aims of this study were to evaluate the accuracy of minimal-preparation CT in identifying colorectal carcinoma in this population and to determine the clinical indications and radiological signs with the highest yield for tumour. The CT technique involved helical acquisition (10-mm collimation, 1.5 pitch) following 2 days of preparation with oral contrast medium only. The outcome of 4 years of experience was retrospectively reviewed. The gold standards were pathological and cancer registration records, together with colonoscopy and barium enema when undertaken, with a minimum of 15 months follow-up. One thousand seventy-seven CT studies in 1031 patients (median age 80 years) were evaluated. CT correctly identified 83 of the 98 colorectal carcinomas in this group but missed 15 cases; sensitivity and specificity (with 95% confidence interval) 85% (78-92%) and 91% (90-93%), respectively. Multivariate analysis identified: (a) a palpable abdominal mass and anaemia to be the strongest clinical indications, particularly in combination (p<0.0025); and (b) lesion width and blurring of the serosal margin of lesions to be associated with tumours (p<0.0001). Computed tomography has a valuable role in the investigation of frail and otherwise disabled patients with symptoms suspicious for a colonic neoplasm. Although interpretation can be difficult, the technique is able to exclude malignancy with good accuracy.

Aged↗
PubMed2002

Improving risk assessment: hip geometry, bone mineral distribution and bone strength in hip fracture cases and controls. The EPOS study. European Prospective Osteoporosis Study.

Hip geometry and bone mineral density (BMD) have previously been shown to relate independently to hip fracture risk. Our objective was to determine by how much hip geometric data improved the identification of hip fracture. Lunar pencil beam scans of the proximal femur were obtained. Geometric and densitometric values from 800 female controls aged 60 years or more (from population samples which were participants in the European Prospective Osteoporosis Study, EPOS) were compared with data from 68 female hip fracture patients aged over 60 years who were scanned within 4 weeks of a contralateral hip fracture. We used Lunar DPX 'beta' versions of hip strength analysis (HSA) and hip axis length (HAL) applied to DPX(L) data. Compressive stress (Cstress), calculated by the HSA software to occur as a result of a typical fall on the greater trochanter, HAL, body mass index (BMI: weight/(height)2) and age were considered alongside femoral neck BMD (FN-BMD, g/cm2) as potential predictors of fracture. Logistic regression was used to generate predictors of fracture initially from FN-BMD. Next age, Cstress (as the most discriminating HSA-derived parameter), HAL and BMI were added to the model as potentially independent predictors. It was not necessary to include both HAL and Cstress in the logistic models, so the entire data set was examined without excluding the subjects missing HAL measurements. Cstress combined with age and BMI provided significantly better prediction of fracture than FN-BMD used alone as is current practice, judged by comparing areas under receiver operating characteristic (ROC) curves (p<0.001, deLong's test). At a specificity of 80%, sensitivity in identification was improved from 66% to 81%. Identifying women at high risk of hip fracture is thus likely to be substantially enhanced by combining bone density with age, simple anthropometry and data on the structural geometry of the hip. HSA might prove to be a valuable enhancement of DXA densitometry in clinical practice and its use could justify a more proactive approach to identifying women at high risk of hip fracture in the community.

Absorptiometry, Photon↗