Slow-rotation dynamic SPECT with a temporal second derivative constraint.

PURPOSE: Dynamic tracer behavior in the human body arises as a result of continuous physiological processes. Hence, the change in tracer concentration within a region of interest (ROI) should follow a smooth curve. The authors propose a modification to an existing slow-rotation dynamic SPECT reconstruction algorithm (dSPECT) with the goal of improving the smoothness of time activity curves (TACs) and other properties of the reconstructed image. METHODS: The new method, denoted d2EM, imposes a constraint on the second derivative (concavity) of the TAC in every voxel of the reconstructed image, allowing it to change sign at most once. Further constraints are enforced to prevent other nonphysical behaviors from arising. The new method is compared with dSPECT using digital phantom simulations and experimental dynamic 99mTc -DTPA renal SPECT data, to assess any improvement in image quality. RESULTS: In both phantom simulations and healthy volunteer experiments, the d2EM method provides smoother TACs than dSPECT, with more consistent shapes in regions with dynamic behavior. Magnitudes of TACs within an ROI still vary noticeably in both dSPECT and d2EM images, but also in images produced using an OSEM approach that reconstructs each time frame individually, based on much more complete projection data. TACs produced by averaging over a region are similar using either method, even for small ROIs. Results for experimental renal data show expected behavior in images produced by both methods, with d2EM providing somewhat smoother mean TACs and more consistent TAC shapes. CONCLUSIONS: The d2EM method is successful in improving the smoothness of time activity curves obtained from the reconstruction, as well as improving consistency of TAC shapes within ROIs.

Lumbar disc herniation mimicking meralgia paresthetica: case report.

BACKGROUND: Meralgia paresthetica, a syndrome of pain and/or dysesthesia in the anterolateral thigh, is normally caused by an entrapment of the lateral femoral cutaneous nerve (LFCN) at the anterior superior iliac spine. In a few cases compression of the nerve in the retroperitoneum has been reported to mimic meralgia paresthetica. CASE DESCRIPTION: A 67-year-old woman presented with a 5-year history of permanent paresthesia in the anterolateral thigh. Motor weakness was not detected. Electromyography showed a neurogenic lesion at the level of L3. Lumbar spine MRI detected a foraminal-extraforaminal disc herniation at L2/L3, which was extirpated via a lateral transmuscular approach. The patient was free of symptoms on the first postoperative day. CONCLUSION: In patients with meralgia paresthetica we emphasize a complete radiological investigation of the lumbar spine, including MRI, to exclude radicular compression by a disc herniation or a tumour at the level of L2 or L3.

Preservation of cranial nerve function following Gamma Knife radiosurgery for benign skull base meningiomas: experience in 121 patients with follow-up of 5 to 9.8 years.

INTRODUCTION: Microsurgical excision with preservation of juxtaposed neurovascular structures is considered the treatment of choice for skull base meningiomas, but there exists a great controversy regarding surgical resectability, potential risk for subsequent postoperative Cranial Nerve Deficit (CND) and the role of adjuvant or adjunctive treatment options. In this study we evaluated the effect of Gamma Knife Radiosurgery (GKRS) in 121 patients with benign basal meningiomas after a follow-up of 5 to 9.8 years. METHODS: Sixty patients had undergone open resections prior to radiosurgical treatment and 61 patients were treated by GKRS alone. Tumour volumes of 0.5 to 89.9 ccm (median 6.8 ccm) received a median marginal dose of 13 Gy (range 7-25 Gy) at the covering 25% to 80% isodose volume curves (median 45%). RESULTS: Neuroradiological controls demonstrated decreased tumour size in 73 patients (60.3%), stable meningioma volume in 47 cases (38.9%) and tumour enlargement in one patient (0.8%). Clinically, 54 patients (44.6%) improved and 61 cases (50.4%) remained unchanged. Four patients (3.3%) showed temporary and two patients (1.7%) permanent neurological deterioration (unrelated to tumour or treatment in one patient). Two patients (1.7%) developed radiation induced new or aggravated pre-existent CND (1 transient, 1 permanent) and two patients (1.7%) required further surgical resection. CONCLUSION: In our long-term experience, GKRS proved to be an attractive additional and save alternative primary treatment option in selected patients with basal meningiomas. The tumour control rate of 98.3% associated with excellent clinical outcome and low incidence for treatment related CND (1.7%) compares favourably with the reported microsurgical series.

The role of Gamma Knife radiosurgery in the management of glomus jugular tumours.

BACKGROUND: Glomus jugular tumours are usually managed by microsurgical resection and/or radiotherapy with considerable risk for treatment-related morbidity. The role of Gamma Knife Radiosurgery (GKRS) in the management of these lesions remains to be defined. METHOD: Between May 1992 and November 2000, 19 patients with glomus tumours underwent GKRS at our department. Nine patients received radiosurgery for residual or recurrent paragangliomas following microsurgical resection and in 10 cases GKRS was performed as primary treatment. The median tumour volume was 5.22 ccm (range: 0.38-33.5 ccm). Marginal doses of 12-20 Gy (median 14 Gy) were applied to enveloping isodose volume curves (Range: 30-55%, median 50%). FINDINGS: Except for an 81-year-old patient who died 9 months after radiosurgery the observation time ranged from 1.5 to 10 years (median 7.2 yrs). The total tumour control rate was 94.7% (7 cases with decreased and 11 with stable tumour size). The only patient with tumour progression (5.3%) underwent repeated radiosurgical treatment 85 months after initial GKRS. A newly diagnosed second lesion in the cavernous sinus was treated radiosurgically as well 53 months after the first Gamma Knife procedure. On clinical examination 10 patients (52.6%) presented with improved and 8 patients (42.1%) with unchanged neurological status. Deterioration in one patient (5.3%) was not related to tumour or radiosurgery. INTERPRETATION: As GKRS demonstrated to be a minimally invasive treatment alternative to microsurgery and radiotherapy with no acute or chronic toxicity it should be considered more frequently in the primary or adjuvant strategy for glomus jugular tumours.

Effects of attenuation in single slow rotation dynamic SPECT.

Dynamic imaging using SPECT has been a topic of research interest for many years. Several proposed approaches have considered the reconstruction of dynamic images from SPECT data acquired with a conventional single slow rotation of the camera, which results in an extremely underdetermined reconstruction problem. Accurate attenuation correction (AC) is particularly important in this context, in order to distinguish the actual dynamic behavior of the tracer within a region from the effects of attenuation on the projection data as the camera rotates around the patient. In this paper, we demonstrate that the standard approach to AC used in conventional SPECT imaging is not sufficient to account for the effects of attenuation in dynamic imaging of this type. As a result, artifacts may be created in the reconstructed images. Using realistic dynamic 3D phantom simulations, as well as real-life dynamic renal SPECT data, we assess the severity of these artifacts and investigate a method to eliminate them. The proposed method is shown to substantially improve the accuracy of the reconstructed image.