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Biomedical subjects

P L Choyke

Publications and source records attributed to P L Choyke.

At least 19 recordsLinked to original sources
PubMed2001

Preferential arterial imaging using gated thick-slice gadolinium-enhanced phase-contrast acquisition in peripheral MRA.

PURPOSE: To investigate the feasibility of preferential arterial imaging using gadolinium-enhanced thick-slice phase-contrast imaging. METHODS: Six healthy volunteers were studied using a peripheral-gated segmented k-space CINE phase-contrast pulse sequence using four views per RR interval with flow encoding in the superior-inferior direction. Images at the level of the popiteal trifurcation were acquired postcontrast with different section thicknesses (4-8 cm) and VENC values (20-150 cm/sec), and phase-difference processing. RESULTS: The post-gadolinium contrast-enhanced thick-slice phase-contrast acquisitions demonstrated the ability to visualize the tibio-peroneal (trifurcation) arteries, especially in systole. With MR contrast agents, the signal from blood is raised significantly above that of stationary tissue from T(1) shortening such that the partial volume artifact is reduced in thick-slice acquisitions. Furthermore, by selecting the VENC value as a function of the cardiac cycle, the noise floor can be raised to selectively suppress flow values less than that of the noise threshold, allowing better accentuation of arterial structures at systole. CONCLUSIONS: Thick-slice phase-contrast acquisition with phase-difference processing has been observed to reduce partial volume artifacts when an MR contrast agent substantially increases signal in the vasculature over that of normal background tissue. Preferential arterial images can be obtained by either increasing the VENC value to selectively suppress signal from slow flow in the veins or by subtracting the diastolic phase image from the peak systolic phase image. J. Magn. Reson. Imaging 2001;13:714-721.

Adult↗
PubMed2001

A prospective analysis of plasma endostatin levels in colorectal cancer patients with liver metastases.

BACKGROUND: Circulating inhibitors of angiogenesis have been suggested to affect the growth of distant micrometastatic disease in patients with cancer. This study was designed to evaluate circulating endostatin levels in colorectal cancer patients with liver metastases. METHODS: Plasma samples from 30 colorectal cancer patients with liver metastases were analyzed for endostatin and vascular endothelial growth factor (VEGF) by using competitive enzyme immunoassays. Samples were compared with plasma from age- and sex-matched healthy controls; values >2 SD above the control mean were considered elevated. RESULTS: Plasma endostatin levels were significantly higher in the 30 cancer patients than controls (P < .0001) and correlated with preoperative VEGF levels (P = .0008). Eighteen patients underwent surgical treatment (liver resection, n = 10; or isolated hepatic perfusion with melphalan, n = 8). Seventeen treated patients were available for follow-up. Eight of 11 patients who progressed had elevated plasma endostatin levels at the time of progression. None of six patients who remained progression free had elevated endostatin levels at last follow-up (P = .02). CONCLUSIONS: Plasma endostatin levels are elevated in colorectal cancer patients with liver metastases and correlate with VEGF levels. Elevated endostatin levels during follow-up are associated with disease progression. Understanding the role of endogenous endostatin in cancer patients may lead to novel strategies to inhibit tumor angiogenesis.

Adult↗
PubMed2001

Merging of intersecting triangulations for finite element modeling.

Surface mesh generation over intersecting triangulations is a problem common to many branches of biomechanics. A new strategy for merging intersecting triangulations is described. The basis of the method is that object surfaces are represented as the zero-level iso-surface of the distance-to-surface function defined on a background grid. Thus, the triangulation of intersecting objects reduces to the extraction of an iso-surface from an unstructured grid. In a first step, a regular background mesh is constructed. For each point of the background grid, the closest distance to the surface of each object is computed. Background points are then classified as external or internal by checking the direction of the surface normal at the closest location and assigned a positive or negative distance, respectively. Finally, the zero-level iso-surface is constructed. This is the final triangulation of the intersecting objects. The overall accuracy is enhanced by adaptive refinement of the background grid elements. The resulting surface models are used as support surfaces to generate three-dimensional grids for finite element analysis. The algorithms are demonstrated by merging arterial branches independently reconstructed from contrast-enhanced magnetic resonance images and by adding extra features such as vascular stents. Although the methodology is presented in the context of finite element analysis of blood flow, the algorithms are general and can be applied in other areas as well.

Algorithms↗
PubMed2001

Contrast-enhanced magnetic resonance angiography: technical considerations for optimized clinical implementation.

Contrast-enhanced magnetic resonance angiography (CE MR angiography) has benefited from advancements in MR imaging speed, pulse sequence design, and dedicated equipment and algorithms for its performance. These improvements have greatly expanded the number of options available to the operator and enabled the application of CE MR angiography to a broader range of clinical applications. In this article, the various timing options, pulse sequence innovations, and contrast administration concerns related to clinical CE MR angiography are reviewed. Pertinent issues related to multiphase and multistation bolus chase CE MR angiography also will be discussed.

Contrast Media↗
PubMed2001

Intraoperative ultrasound during renal parenchymal sparing surgery for hereditary renal cancers: a 10-year experience.

PURPOSE: We review our 10-year experience with intraoperative ultrasound during renal parenchymal sparing surgery in patients with hereditary renal cancers. MATERIALS AND METHODS: Between 1991 and 2000, 68 nephron sparing procedures were performed on 26 women and 27 men, all but 1 of whom had a hereditary predisposition to renal cancer, for example von Hippel-Lindau, hereditary papillary renal cancer. Intraoperative ultrasound was performed after the surgeon removed all visible or palpable lesions. High frequency transducers (7 MHz.) and color Doppler were used in all cases. Lesions were characterized as simple cysts, complex cysts or solid masses, and were recorded on a map. RESULTS: A total of 935 lesions (mean 12.8 lesions per kidney) were removed in 68 nephron sparing operations performed on 53 patients. Of these lesions 870 were removed without while 65 required intraoperative ultrasound. In 17 of 68 (25%) procedures intraoperative ultrasound identified renal cancers that were not detectable by the surgeon. Mean tumor size of ultrasound detected lesions was 1.0 cm. (range 2 mm. to 4 cm.). Of the 32 cystic lesions identified by intraoperative ultrasound 5 contained renal carcinoma, and 29 of the 33 solid renal masses were renal cell carcinomas. During reoperations ultrasound enabled the surface of the kidney to be evaluated even when it was inaccessible due to scar tissue or adherent perinephric fat. CONCLUSIONS: Intraoperative ultrasound can be performed after all visible lesions have been removed and identifies additional tumors in 25% of patients with hereditary renal cancer, thus ensuring that as many tumors as possible have been removed during renal parenchymal sparing surgery.

Carcinoma, Renal Cell↗
PubMed2001

Intraoperative ultrasound of the kidney.

Intraoperative ultrasound is a useful method of identifying renal masses during partial nephrectomy. It can be used to locate primary lesions, identify satellite lesions, assess for peritumoral vascularity and venous invasion. As nephron-sparing surgery becomes more widespread, intraoperative ultrasound of the kidneys will become more commonplace.

Journal Article↗
PubMed2001

Vessel surface reconstruction with a tubular deformable model.

Three-dimensional (3-D) angiographic methods are gaining acceptance for evaluation of atherosclerotic disease. However, measurement of vessel stenosis from 3-D angiographic methods can be problematic due to limited image resolution and contrast. We present a method for reconstructing vessel surfaces from 3-D angiographic methods that allows for objective measurement of vessel stenosis. The method is a deformable model that employs a tubular coordinate system. Vertex merging is incorporated into the coordinate system to maintain even vertex spacing and to avoid problems of self-intersection of the surface. The deformable model was evaluated on clinical magnetic resonance (MR) images of the carotid (n = 6) and renal (n = 2) arteries, on an MR image of a physical vascular phantom and on a digital vascular phantom. Only one gross error occurred for all clinical images. All reconstructed surfaces had a realistic, smooth appearance. For all segments of the physical vascular phantom, vessel radii from the surface reconstruction had an error of less than 0.2 of the average voxel dimension. Variability of manual initialization of the deformable model had negligible effect on the measurement of the degree of stenosis of the digital vascular phantom.

Carotid Arteries↗
PubMed2001

High-spatial-resolution multistation MR imaging of lower-extremity peripheral vasculature with segmented volume acquisition: feasibility study.

A method of three-station three-dimensional magnetic resonance (MR) angiography of the lower extremities with segmented volume acquisition is presented. Three-dimensional MR angiographic data were acquired in two passes, with the central k-space views acquired during the arterial phase for the more proximal stations. This allowed a faster bolus injection rate and potentially improved visualization of the tibioperoneal arteries.

Adult↗
PubMed2001

Hepatic MR angiography: a multiobserver comparison of visualization methods.

OBJECTIVE: MR angiography (MRA) is an established diagnostic method; however, controversy remains over the best technique for display. In this study, we compared five methods of depicting hepatic MRA, including a novel skeletonization approach, using receiver operator characteristic (ROC) curves, interobserver variability (kappa values), and speed of interpretation. SUBJECTS AND METHODS: Twenty-one patients scheduled for isolated liver perfusion therapy for metastatic disease underwent contrast-enhanced three-dimensional MRA to determine vascular anatomy. Vascular anatomy was validated at the time of surgery. We displayed the image data, using five techniques: maximum intensity projection, targeted maximum intensity projection, isointensity surface (isosurface), connected isointensity surface (connected isosurface), and ordered region growing skeleton (skeleton). Four observers, blinded to the surgical results, interpreted each technique in random order without patient identifiers. Areas under the ROC curves, kappa values of interobserver variability, and time to interpret each display were compared. RESULTS: Skeletonized MRA had the highest area under the ROC curve (A(z), 0.90 +/- 0.04) compared with the other techniques (p < 0.013). Kappa scores of agreement were also highest for skeletonized MRA (0.75 +/- 0.04) and had no overlap at the 95% confidence level compared with other techniques. Compared with source images, all visualization methods were faster to interpret, but the skeleton technique was more quickly (p = 0.04) interpreted than the other techniques. CONCLUSION: Skeletonized MRA with the skeleton connectivity algorithm is a semi-automated method of displaying complex arterial anatomy. Compared with other techniques, it is more accurate, more consistent among observers, and slightly faster to interpret. Skeletonization should be applicable to CT angiography and MRA.

Female↗
PubMed2001

Parenchymal sparing surgery in patients with hereditary renal cell carcinoma: 10-year experience.

PURPOSE: von Hippel-Lindau disease, hereditary papillary renal cell carcinoma, the Birt-Hogg-Dubé syndrome and familial renal oncocytoma are familial renal tumor syndromes. These hereditary disorders are noteworthy for the development of multiple bilateral renal tumors and the risk of new tumors throughout life. One management strategy is observation of solid renal tumors until reaching 3 cm, then performing parenchymal sparing surgery. We present a 5-year update on our experience. MATERIALS AND METHODS: From May 1988 to October 1998, 49 patients with hereditary renal cell carcinoma, including von Hippel-Lindau disease in 44, hereditary papillary renal cell carcinoma in 4 and the Birt-Hogg-Dubé syndrome in 1, and 1 with familial renal oncocytoma underwent exploration to attempt renal parenchymal sparing surgery. Patients were followed prospectively with periodic screening for recurrence, metastasis and loss of renal function. Median followup was 79.5 months (range 0.7 to 205). RESULTS: A total of 50 patients underwent 71 operations resulting in unilateral nephrectomy in 6, bilateral nephrectomy in 1 and partial nephrectomy in 65, with 1 to 51 tumors removed from each kidney (mean 14.7). Mean patient age was 39.5 years (range 18 to 70). Of the 65 (40%) partial nephrectomies 26 were performed with cold renal ischemia. Mean blood loss was 2.9 +/- 0.5 l (range 0.15 to 23). Postoperative complications included renal atrophy in 3 patients. Mean preoperative serum creatinine was 1.05 +/- 0.03 mg/dl (range 0.6 to 1.8), and postoperative creatinine was 1.06 +/- 0.04 mg/dl (range 0.6 to 2.0). No patient who underwent renal parenchymal sparing surgery required renal replacement therapy. Metastatic disease developed in 1 patient with a 4.5 cm renal tumor. CONCLUSIONS: Parenchymal sparing surgery with a 3 cm threshold in patients with hereditary renal cancer appears to be an effective therapeutic option to maximize renal function while minimizing the risk of metastatic disease.

Adolescent↗
PubMed2001

Retroperitoneoscopic-guided radiofrequency ablation of renal tumors.

OBJECTIVE: Minimally invasive approaches to the management of renal tumors are being studied intensively in urology. Herein, we describe the use of multiple organ-sparing techniques for the management of tumors in a patient with von Hippel Lindau disease (VHL). MATERIALS AND METHODS: A 42 year-old woman with VHL underwent a right partial adrenalectomy and a left renal radiofrequency ablation (RFA) of two renal tumors. RESULTS: A 2.2 cm solitary right adrenal pheochromocytoma was resected using a transperitoneal approach. A retroperitoneal approach to the left kidney was performed and RFA of the two renal tumors completed using sonographic guidance. On the 5-month follow-up CT scan, there was no evidence of residual adrenal tumors and both renal lesions lacked contrast enhancement. No complications occurred during the post-operative recovery. CONCLUSIONS: Multiple organ-ablative laparoscopic procedures may be performed in a single sitting. Laparoscopic partial adrenalectomy is an effective technique in patients with bilateral tumors or a familial syndrome predisposing to multiple adrenal tumors. Further study of renal RFA is required to assess the long-term durability of the procedure.

Adrenal Gland Neoplasms↗
PubMed2000

Bolus-chase peripheral 3D MRA using a dual-rate contrast media injection.

In this pilot study, using a standard 40 mL gadolinium (Gd) chelate contrast dose, dual-rate (first 20 mL at 0.5 mL/sec; remaining 20 mL at 1.5 mL/sec) and fixed-rate (entire 40 mL dose at either 0.7 mL/sec or 2.0 mL/sec) injection schemes for multistation, bolus-chase magnetic resonance angiography (MRA) were compared in normal volunteers. Signal-to-noise ratio, contrast-to-noise ratio, and physician preference were determined for nine arterial segments. At the terminal station (calf), the dual-rate contrast injection improved arterial signal and contrast compared with both fixed-rate injection schemes and improved subjective vessel appearance compared with the 2.0 mL/sec, but not the 0.7 mL/sec, fixed-rate scheme.

Adult↗
PubMed2000

Acquired cystic kidney disease.

Acquired cystic kidney disease (ACKD), also known as acquired renal cystic disease (ARCD,) occurs in patients who are on dialysis for end-stage renal disease. It is generally accepted that ACKD develops as a consequence of sustained uremia and can first manifest even before dialysis is initiated while the patient is still in chronic renal failure. The role of immune suppression, particularly in transplant recipients, in the development of ACKD, is still under investigation. The prevalence of ACKD is directly related to the duration of dialysis and the risk of cancer is directly related to the presence of cysts. Herein we review the current understanding of the pathophysiology and imaging implications of ACKD.

Diagnostic Imaging↗
PubMed2000

Histopathology and molecular genetics of multiple cysts and microcystic (serous) adenomas of the pancreas in von Hippel-Lindau patients.

Microcystic adenoma and cysts of the pancreas occur sporadically or as a part of von Hippel-Lindau (VHL) disease. The pathology of pancreatic cystic disease in VHL patients has not been well characterized. Furthermore, it is presently unknown whether the alteration of the VHL gene is responsible for the development of the entire spectrum of pancreatic serous cystic lesions. We performed a histopathological analysis of 21 cysts and 98 microcystic adenomas in nine VHL patients with a known germline mutation. In addition, PCR-amplified DNA from 27 pancreatic cystic lesions in three informative patients was studied for allelic deletions with polymorphic markers spanning the VHL gene locus. In all patients, pancreatic lesions were multiple: 21 benign serous cysts, 63 microscopic microcystic adenomas (size <0.4 cm), and 35 macroscopic microcystic adenomas (size >0.5 cm). The average number of lesions per patient was 2.1 benign cysts (range, 0-8), 7.7 (1-37) microscopic microcystic adenomas, and 3 (0-21) macroscopic microcystic adenomas. All lesions showed similar histology and contained prominent fibrous stroma, clear and/or amphophilic, glycogen-rich epithelial cells, endothelial and smooth muscle cells. VHL deletions were detected in all types of pancreatic cystic lesions. The presence of VHL gene allelic deletions in the spectrum of multifocal pancreatic cystic lesions provides direct molecular evidence of their neoplastic nature and integral association with VHL disease. The histopathological and molecular data establish a serous cyst-microcystic adenoma continuum in the development of pancreatic cystic neoplasia in VHL disease.

Adenoma↗