Browsing by Author "Doruyter, Alexander Govert George"

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    Imaging of renal hyperparathyroidism using SPECT/CT with low-dose localizing CT
    (Stellenbosch : Stellenbosch University, 2013-12) Doruyter, Alexander Govert George; Warwick, James Matthew; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medical Imaging and Clinical Oncology. Division of Nuclear Medicine.
    ENGLISH ABSTRACT: Background: Hybrid imaging using single photon emission computed tomography/low dose (x-ray) computed tomography (SPECT/LDCT) is of benefit in preoperative scintigraphy of primary hyperparathyroidism. The role of SPECT/LDCT in preoperative assessment of renal hyperparathyroidism has not yet been examined. The aim of the study was to determine whether SPECT/LDCT conferred any benefit over SPECT alone in terms of detection and/or localization of hyperfunctioning parathyroid tissue in this patient group. Methods: A retrospective study of patients with renal hyperparathyroidism and positive planar and SPECT scintigraphy was undertaken. All patients underwent planar scintigraphy using 99mTc-pertechnetate immediately followed by 99mTc-sestamibi as well as SPECT/LDCT 60 min after sestamibi injection and a delayed static image to assess for differential washout at 2-3 hours. Planar subtraction images were generated. For each patient, two nuclear physicians reported on planar+ SPECT images followed by planar + SPECT/LDCT images (assisted by a radiologist). Confidence for the presence of hyperfunctioning parathyroid tissue as well as confidence of location was scored on a Likert-type scale. Interpretation of planar + SPECT was compared with interpretation of planar + SPECT/LDCT. The impact of LDCT on equivocal lesions and number of ectopic lesions detected was also assessed. Results: Twenty patients (M:13; F:7) imaged between February 2008 and June 2011 were included [mean age: 40 years (24 – 55)]. Mean creatinine was 687 μmol/l (169-1213), mean corrected calcium: 2.55 mmol/l (1.95-3.33) and median PTH 167 pmol/l (2.4 - >201). Thirty-five lesions were detected on planar and SPECT and this was unchanged after assessment of the LDCT data. Confidence for the presence of parathyroid pathology changed in 5 patients (5 lesions) with the addition of LDCT. LDCT changed the mean confidence of parathyroid pathology from 3.17 to 3.29 (p=0.16). Addition of LDCT reduced the number of equivocal lesions from 18 (14 patients) to 14 (10 patients) (p=0.13). The addition of LDCT changed localization in 4 lesions (3 patients). Confidence in localization of pathology changed in 9 lesions (7 patients) and the mean localization confidence score was improved from 4.2 to 4.46 (p=0.002) with LDCT. The number of lesions classified as ectopic increased from 5 (on planar+SPECT) to 8 (with addition of LDCT) (p=0.25). Conclusion: In renal hyperparathyroidism SPECT/LDCT altered localization of lesions detected on planar and SPECT alone and improved reader confidence of localization accuracy. SPECT/LDCT conferred no additional benefit over SPECT in terms of detection, confidence of parathyroid pathology or ability to distinguish equivocal from non-equivocal parathyroid lesions. The addition of LDCT did not detect significantly more ectopic lesions. Whereas the minor improvement in reader confidence of localization (with addition of LDCT) was of questionable clinical significance, we speculate that the changed and presumably improved localization of lesions on SPECT/LDCT had potential clinical impact in a significant proportion of patients. On this basis we recommend the use of hybrid SPECT/LDCT in imaging of renal hyperparathyroidism when surgery is considered.
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    Social anxiety disorder : Functional neuroimaging and social cognitive features
    (Stellenbosch : Stellenbosch University, 2018-03) Doruyter, Alexander Govert George; Warwick, James Matthew; Lochner, Christine; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medical Imaging and Clinical Oncology. Nuclear Medicine.
    ENGLISH SUMMARY : Neuroimaging has enabled important progress in understanding the neurobiology of social anxiety disorder (SAD). Functional neuroimaging experiments in SAD have mostly focused on regional neural activity in response to anxiety provocation or processing of emotional faces, and have found hyper-activations in limbic and paralimbic circuitry. Relatively little however, is known about resting-state conditions in SAD and how these are affected by pharmacotherapy. What is known is almost entirely based on functional magnetic resonance imaging (fMRI) techniques which, while powerful, have some important limitations. Similarly, there has been only limited work investigating the resting neural correlates of social cognitive biases in SAD; how reward processing is disrupted in the condition; and how these respective features are affected by therapy. This thesis presents the first work on SAD investigating resting functional connectivity (RFC) based on nuclear neuroimaging methods. In an experiment that analysed RFC based on single photon emission computed tomography with technetium-99m hexamethyl propylene amine oxime, it was found that RFC differences in SAD were largely consistent with a contemporary network model based on fMRI, as well as implicating disrupted connectivity of the cerebellum. Another novel finding was how pharmacotherapy in SAD increased RFC of the anterior cingulate cortex. Using graph theory and resting-state fMRI, the first evidence of reduced global efficiency and increased clustering coefficients within the theory-of-mind network in SAD as well as independent evidence of social attribution bias in the same sample were reported. In an experiment that investigated regional resting metabolism in the disorder, there was evidence of abnormality in SAD compared to controls, as well as evidence of pharmacotherapy effects, in several biologically relevant regions. These results merit further investigation. Finally, in an fMRI-based experiment on reward processing in SAD, initial results identified no evidence of disrupted processing on a monetary reward task. The findings here support a neurobiological model of SAD in which alterations in resting regional metabolism may underlie disruptions in resting brain networks that have been implicated as being important in social cognitive processing. The results also suggest that pharmacotherapy may affect resting-state conditions through compensatory effects. Finally, the provisional findings are consistent with the theory that reward deficits in SAD may be limited to the processing of social reward, and may not extend to the processing of other reward types. Future SAD research should focus on collaborative work, using pooled datasets, and place greater emphasis on molecular disruptions in neurotransmitter systems involved in the disorder.