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J M Hawnaur

Publications and source records attributed to J M Hawnaur.

18 recordsLinked to original sources
PubMed1997

Contrast-modified gradient echo imaging using rotary echo preparatory pulses.

The use of on-resonance 121 binomial composite pulses in two- or three-dimensional magnetization-prepared gradient-recalled echo magnetic resonance imaging experiments generates rotary echoes, leading to an increase in contrast range that is, in part, determined by the ratio of T2 to T1. In comparison with other fast gradient-recalled echo imaging techniques designed for enhanced T2 contrast, this method is more robust with respect to radiofrequency field inhomogeneity and less sensitive with respect to motion artifacts. Three-dimensional parametric images may be calculated using least-squares fitting based on a simple model for steady-state longitudinal magnetization during the imaging sequences.

Brain↗
PubMed1997

MR angiography and MR imaging of symptomatic vascular malformations.

PURPOSE: To define the appearance of peripheral vascular malformations at magnetic resonance angiography (MRA) and assess the role of magnetic resonance imaging (MRI) and MRA in the investigation of these lesions. PATIENTS AND METHODS: Fourteen patients (aged 8-51 years) with clinical evidence of a vascular malformation were referred for MRI and MRA, performed on a 0.5T GE Vectra superconducting system (International General Electric, Slough, UK). Multisection T1-weighted spin-echo and T2-weighted fast spin-echo pulse sequences were performed, with an inversion recovery fast spin-echo sequence in two cases. Two-dimensional time of flight (2-D TOF) and/or 2-D phase contrast (PC) MRA was performed in 13 cases. Eleven patients had digital subtraction angiography (DSA) using a Phillips Integris V3000 digital angiographic unit. The findings at MRA and MRI were compared with the catheter angiograms, and the effective diagnostic input of MRA and MRI was determined. RESULTS: MRA demonstrated major feeding vessels and multiple intra-lesional vessels in relation to the high flow lesions, features absent in the low flow lesions. However, small feeding vessels to the AVMs were not clearly identified. MRI gave a clear demonstration of the anatomical extent of all lesions. AVMs (n = 6) and venous malformations (n = 6) were reliably distinguished, the former containing multiple serpentine signal voids on T1- and T2-weighted imaging, the latter being hyperintense to fat on T2-weighted images. Two other high-flow lesions diagnosed clinically as vascular malformations appeared solid on MRI, and were diagnosed histologically as a carotid body tumour and an angiomyolipoma. CONCLUSION: Although 2-D TOF MRA can distinguish AVMs from venous malformations, the technique adds little extra practical information to the diagnostic process, and cannot compete with catheter angiography for the detailed demonstration of AVM feeding vessels. These lesions can also be characterized using spin-echo sequences, though the primary role of MRI is to demonstrate their anatomical extent.

Adolescent↗
PubMed1996

Skin: MR imaging findings at middle field strength.

Skin tumors were staged at magnetic resonance (MR) imaging on a 0.5-T (middle-field-strength) system, with use of a 2-cm-diameter receive-only surface coil. T1- and T2-weighted spin-echo (SE), fast SE, or three-dimensional (3D) spoiled gradient-recalled imaging were performed in three volunteers and in 13 patients with skin tumors (nine, basal cell carcinoma). MR findings correlated well with histologic findings in the patients (epidermis, relatively hyper-intense on all images; dermis, hypo-intense with irregular interface with subdermal fat). 3D images had the optimal combination of tissue contrast, signal-to-noise ratio, and spatial resolution. MR imaging depicts depth of skin tumor invasion, and findings are complementary to clinical staging.

Adult↗
PubMed1995

Superparamagnetic iron oxide imaging of focal liver disease.

The use of iron oxide as a superparamagnetic contrast agent for magnetic resonance imaging of the liver has been described previously. When administered intravenously, superparamagnetic iron oxide (SPIO) is sequestered by the reticuloendothelial system causing significant shortening of the T2-relaxation time. The majority of the contrast is taken up by the reticuloendothelial tissue of the liver. Since tumours have reduced or absent reticuloendothelial tissue the effect on relaxation time is minimal and signal intensity differences between tumour and liver are increased. AMI 25 (Laboratoire Guerbet, Paris) is a colloidal solution of ferrous and ferric oxides. We have performed MR examination of the liver in 16 patients with focal liver lesions using AMI 25 as a superparamagnetic contrast agent. Our results indicate that SPIO significantly increases the conspicuity of focal lesions and the effect is greatest in malignant tumours. We observed no adverse reaction to this contrast agent.

Adolescent↗
PubMed1995

Off-resonance binomial composite pulses in 2D and 3D fat/water imaging at 0.5 T.

A new method of acquiring two-dimensional (2D) and three-dimensional (3D) fat/water decomposed images on a 0.5 T magnetic resonance (MR) imaging system is described. The method uses a gradient-recalled echo (GRE) sequence incorporating a composite 121 pulse, originally used for magnetization transfer contrast (MTC) experiments, for frequency-selective pre-saturation. By applying the 121 pulse off resonance, a sharp discrimination between the chemically shifted water and fat signals may be obtained using a composite pulse as short as 4 ms. Phantom studies demonstrate that suppression ratios as high as 50:1 are achievable. The new method has been applied to volunteers and patients, and good fat/water images of limb, abdomen, head and neck obtained. The new method can be incorporated into other pulse sequences related to GRE, such as phase contrast (PC) and time-of-flight (TOF), and represents the first practical (i.e. rapid) method for 3D fat/water imaging at an operating field as low as 0.5 T.

Adipose Tissue↗
PubMed1994

Staging, volume estimation and assessment of nodal status in carcinoma of the cervix: comparison of magnetic resonance imaging with surgical findings.

Pre-operative magnetic resonance imaging (MRI) was carried out in 50 women scheduled for operative treatment of invasive carcinoma of the cervix. The extent of the primary tumour (stage), its dimensions and the presence of lymph node enlargement were assessed and compared with findings at surgery and/or histopathological examination of the resected uterus. In 45 patients undergoing radical hysterectomy, accuracy of MRI staging of the primary tumour was 84.4%. In the group as a whole, including four patients with inoperable disease, staging accuracy was 84%. Most errors were due to difficulty in identifying early vaginal or parametrial invasion by tumour. There was close correlation between the volume of tumour measured from pre-operative MRI scans and measurements made on the hysterectomy specimen (r = 0.95). MRI had a sensitivity of 75% and a specificity of 88% in predicting metastatic lymphadenopathy, based solely on the criterion of enlargement of any pelvic or para-aortic nodes to 1.5 cm or greater. However, retrospective analysis of the presence or absence of metastases by site in 49 patients undergoing lymphadenectomy or lymph node sampling at laparotomy showed that true sensitivity to be 57.1% and the specificity 96.8%. Differentiation between malignant and reactive lymphadenopathy was not reliably achieved on MRI, and in several patients, metastases were present in normal-sized lymph nodes.

Adolescent↗
PubMed1994

Clinical evaluation of fast spin echo sequences for cranial magnetic resonance imaging at 0.5 tesla.

Fast spin echo (FSE) sequences enable T2-weighted MR scans to be obtained in a fraction of the time necessary for conventional SE sequences with long TR and long TE. Comparison has been made of a FSE sequence (TR = 4000 ms, effective TE = 100 ms, 2 NEX) with the T2-weighted SE sequence (TR = 2000 ms, TE = 90 ms, 1-2 NEX) normally used in 35 patients referred for cranial MRI. Contrast-to-noise ratios (CNR) for grey:white matter and brain:CSF on the FSE sequence compared favourably with variable echo (VE) sequences which take up to three times as long to acquire. Although the conspicuity of some pathological lesions such as multiple sclerosis plaques was inferior to that of conventional T2-weighted SE scans, no lesions were missed on FSE scans. The FSE sequence was more prone to movement artefacts. The benefit of the markedly increased patient throughput made possible by using the FSE sequence outweighs the slight reduction in sensitivity for small lesions.

Adult↗
PubMed1994

Magnetic resonance image synthesis using a flexible model.

Image synthesis methods are based on the hypothesis that a magnetic resonance (MR) image with optimized contrast can be reproduced by synthesis from three calculated basic images of T1, T2 and spin density. This method, however, is limited by noise due to uncertainties in the initial measurements. The principal component analysis (PCA) method is based on an information theory approach that decomposes MR images into a small set of characteristic feature images. PCA images, or eigenimages, show morphology by condensing the structural information from the source images. Eigenimages have also been shown to improve contrast-to-noise ratio (CNR) compared with source images. In this study we have developed a method of synthesizing MR images using a flexible model, comprising a set of eigenimages derived from PCA. A matching process has been carried out to find the best fit between the model and a synthetic image calculated from the Bloch equations. The method has been applied to MR images obtained from a group of patients with intracranial lesions. The images derived from the flexible model show increased lesion conspicuity, reduced artefact and comparable CNR to the directly acquired images while maintaining the MR characteristic information for diagnosis.

Adult↗
PubMed1993

Magnetic resonance imaging with Gadolinium-DTPA for assessment of bladder carcinoma and its response to treatment.

Magnetic Resonance Imaging (MRI) with intravenous Gadolinium-DTPA (Gd-DTPA, Magnevist, Schering-AG) was performed in 44 patients, 32 with primary bladder carcinoma and 12 with suspected recurrence after treatment. Gd-DTPA often increased diagnostic confidence in the identification and staging of tumours confined to the bladder wall and was necessary to assess depth of bladder wall invasion when T2-weighted images were suboptimal. Enhancement after Gd-DTPA enabled distinction between necrotic and viable tumour and blood clot. There was little advantage in its use for tumours infiltrating perivesical fat or with metastases to lymph nodes or bone, in the absence of a fat suppression sequence. Gd-DTPA may therefore be useful in selected patients with tumours of Stage T3a or less in whom information about depth of bladder wall invasion is inadequately shown on pre-contrast sequences. Artefacts due to variable and inhomogeneous urine signal intensity, however, often degraded post-Gd-DTPA images of the bladder. Changes in the bladder due to radiotherapy were observed on MRI 3-4 months after treatment in patients referred for routine follow-up and in some patients with suspected recurrence. Mucosal hyperintensity, thickening and abnormal signal intensity of the muscular layers of the bladder wall, with enhancement after Gd-DTPA were demonstrated. Such changes obscured small volume or superficial recurrence of tumour after radiotherapy. Abnormal enhancement was also observed in pelvic organs and soft tissues irradiated several years earlier. Enhancement after Gd-DTPA does not therefore reliably distinguish between recurrent tumour and radiotherapy change.

Aged↗
PubMed1991

Investigation of children with suspected spinal dysraphism by magnetic resonance imaging.

Findings on Magnetic Resonance Imaging (MRI) of 52 children with suspected spinal dysraphism have been reviewed. In 24, no significant spinal abnormality was demonstrated. Seven patients had scoliosis or vertebral segmentation anomalies without demonstrable abnormality of the underlying soft tissues and one had an isolated subcutaneous haemangioma. In 20 children with spinal dysraphism, a low tethered cord was the most frequent finding, occurring in 80%. Other manifestations included myelo- or meningocoele (60%), syringomyelia (30%), lipoma (25%), congenital tumour (20%), diastematomyelia (15%) and thickened filum terminale (5%). The relationship between the clinical reason for requesting MRI and the scan results are discussed.

Adolescent↗
PubMed1990

Musculoskeletal haemangiomas: comparison of MRI with CT.

MRI and CT findings were reviewed from 11 patients with musculoskeletal haemangiomas. With MRI, morphological characteristics and extent of haemangiomas were optimally demonstrated on T2-weighted spin echo scans. High-resolution contrast-enhanced CT provided equivalent information regarding lesional characteristics and extent for small, localized haemangiomas. In CT evaluation of the extent of large haemangiomas, the radiation dose, transaxial scan plane, amount of intravenous contrast medium required and the necessity for correct timing of post-contrast scans became limiting factors. For such lesions, particularly those extending into the trunk, MRI supplemented by a plain radiograph is the optimum method of evaluation.

Adolescent↗
PubMed1990

Magnetic resonance imaging of musculoaponeurotic fibromatosis.

Musculoaponeurotic fibromatosis can be mistaken for soft-tissue sarcoma both clinically and on X-ray computed tomography. Magnetic resonance imaging (MRI) in three patients with this condition enabled the correct diagnosis to be made prospectively in two. The appearance on MRI of a heterogeneous mass with well-defined, predominantly peripheral areas of very low signal intensity due to dense fibrous tissue and areas of medium to high signal intensity corresponding to a more cellular stroma should raise the the suspicion of musculoaponeurotic fibromatosis. Cellular areas within the tumour showed moderate enhancement after gadolinium diethylene triamine pentaacetic acid administration.

Adult↗
PubMed1989

Antenatal ultrasonography to detect fetal renal abnormalities: a prospective screening programme.

OBJECTIVE: To evaluate screening for abnormalities of the fetal renal tract by ultrasonography and to determine the incidence of such abnormalities in a population. DESIGN: A 12 month prospective population study. Follow up of infants to between 9 and 18 months. SETTING: A district general hospital. PARTICIPANTS: 6292 Pregnant women reaching 28 weeks' gestation within the study period. INTERVENTIONS: Antenatal ultrasound scanning was offered to all of the women. Babies in whom an abnormality of the renal tract had been detected antenatally underwent ultrasound scanning at the end of the first week. If the abnormality was confirmed contrast radiography was performed. END POINT: Confirmation of suspected renal abnormality by postnatal investigations. Detection of abnormality in children thought to be normal antenatally. MEASUREMENTS AND MAIN RESULTS: Of the 92 babies who had abnormal antenatal scans, 42 had abnormalities confirmed postnatally. Four of them died and 21 had had or were awaiting an operation at 18 months' follow up. Seven children had renal abnormalities that were missed antenatally. The incidence of abnormalities detected by screening antenatally was 0.65%, and the overall incidence at 18 months' follow up was 0.76%. CONCLUSIONS: The incidence of structural renal abnormalities in babies is higher than reported previously. Antenatal ultrasonography is an effective way of detecting such abnormalities.

England↗
PubMed1983

Reasons for late detection of hip dislocation in childhood.

A retrospective study of 56 children with dislocation of the hip presenting late found that the mean age at which the parents first noticed that something was wrong (including hip abnormalities found at birth in 10 patients) was 11 months, but that at diagnosis was 26 months, a mean delay of 15 months. The reasons for delay were failure to examine the hips at birth (13 cases), failure to follow up abnormalities at birth (7), failure of symptoms noticed by the parents to alert the health-care professional to the possibility of a dislocated hip (36), failure to check the hips routinely after 3 months (27), and failure of the parents to appreciate the significance of abnormalities and to act on them (28). Hip screening should continue beyond the neonatal period and should include routine checks on all children until they are walking normally. A greater awareness in health-care professionals of the features of hip dislocation and further health education for parents are needed.

Adolescent↗