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Biomedical subjects

Klaus D Hagspiel

Publications and source records attributed to Klaus D Hagspiel.

At least 19 recordsLinked to original sources
PubMed2006

Evaluation of emphysema severity and progression in a rabbit model: comparison of hyperpolarized 3He and 129Xe diffusion MRI with lung morphometry.

The apparent diffusion coefficients (ADCs) of hyperpolarized (3)He and (129)Xe gases were measured in the lungs of rabbits with elastase-induced emphysema and correlated against the mean chord length from lung histology. In vivo measurements were performed at baseline and 2, 4, 6, and 8 wk after instillation of elastase (mild and moderate emphysema groups) or saline (control group). ADCs were determined from acquisitions that used two b values. To investigate the effect of b value on the results, b-value pairs of 0 and 1.6 s/cm(2) and 0 and 4.0 s/cm(2) were used for (3)He, and b-value pairs of 0 and 5.0 s/cm(2) and 0 and 10.0 s/cm(2) were used for (129)Xe. At 8 wk after instillation, the rabbits were euthanized, and the lungs were analyzed histologically and morphometrically. ADCs for the rabbits in the control group did not change significantly from baseline to week 8, whereas ADCs for the rabbits in the emphysema groups increased significantly (P < 0.05) for all gas and b-value combinations except (129)Xe with the b-value pair of 0 and 5.0 s/cm(2). The largest percent change in mean ADC from baseline to week 8 (15.3%) occurred with (3)He and the b-value pair of 0 and 1.6 s/cm(2) for rabbits in the moderate emphysema group. ADCs (all b values) were strongly correlated (r = 0.62-0.80, P < 0.001) with mean chord lengths from histology. These results further support the ability of diffusion-weighted MRI with hyperpolarized gases to detect regional and global structural changes of emphysema within the lung.

Animals↗
PubMed2006

Delayed calf muscle phosphocreatine recovery after exercise identifies peripheral arterial disease.

OBJECTIVES: In this study we intend to characterize phosphocreatine (PCr) recovery kinetics with phosphorus-31 ((31)P) magnetic resonance spectroscopy in symptomatic peripheral arterial disease (PAD) patients compared with control subjects and determine the diagnostic value and reproducibility of this parameter. BACKGROUND: Due to the inconsistent relationship between flow and function in PAD, novel techniques focused on the end-organ are needed to assess disease severity and measure therapeutic response. METHODS: Fourteen normal subjects (5 men, age 45 +/- 14 years) and 20 patients with mild-to-moderate symptomatic PAD (12 men, age 67 +/- 10 years, mean ankle brachial index 0.62 +/- 0.13) were studied. Subjects exercised one leg to exhaustion while supine in a 1.5-T magnetic resonance scanner using a custom-built plantar flexion device. Surface coil-localized, free induction decay acquisition localized to the mid-calf was used. Each 31P spectrum consisted of 25 signal averages at a repetition time of 550 ms. The PCr recovery time constant was calculated by monoexponential fit of PCr versus time, beginning at exercise completion. RESULTS: Median exercise time was 195.0 s in normal subjects and 162.5 s in PAD patients (p = 0.06). Despite shorter exercise times in patients, the median recovery time constant of PCr was 34.7 s in normal subjects and 91.0 s in PAD patients. Area under the receiver-operating characteristic curve was 0.925 +/- 0.045. Test-retest reliability was excellent. CONCLUSIONS: The PCr recovery time constant is prolonged in patients with symptomatic PAD compared with normal subjects. The method is reproducible and may be useful in the identification of disease. Further study of this parameter's ability to track response to therapy as well as its prognostic capability is warranted.

Adult↗
PubMed2006

Comparison of multistation MR angiography with integrated parallel acquisition technique versus conventional technique with a dedicated phased-array coil system in peripheral vascular disease.

PURPOSE: To assess the impact of integrated parallel acquisition technique (iPAT) on signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), venous contamination, and overall image interpretability for peripheral magnetic resonance (MR) angiography with use of a dedicated phased-array coil system. MATERIALS AND METHODS: Three-dimensional contrast material-enhanced conventional MR angiography and iPAT peripheral MR angiography was performed at three stations (pelvis, thigh, calf) in 38 consecutive patients on a 1.5-T high-performance cardiovascular system (conventional MR angiography, n=19; iPAT MR angiography, n=19). A total of 29 vessel segments per patient were analyzed. For each segment, arterial, muscle, and background signal were measured; SNR and CNR were calculated; and repeated-measures analysis of variance was performed. For each of the three stations, the degree of venous contamination and the overall confidence of interpretability were analyzed with use of ordinal logistic regression analysis accounting for correlated outcome data. RESULTS: A total of 1,018 vessel segments were available for analysis (477 with conventional MR angiography, 541 with iPAT MR angiography). Compared with conventional MR angiography, iPAT MR angiography resulted in decreased SNR and CNR in the pelvis and thigh stations but no change in the calf station. The difference in the pelvis was statistically significant (P<.007 for SNR and P<0.01 for CNR). Venous contamination in the calf station was significantly less on iPAT MR angiography (P<.003), with no significant differences in the other stations. The overall confidence of interpretability with iPAT MR angiography was significantly better on the lower station (P<.008). CONCLUSIONS: iPAT MR angiography leads to reduced SNR and CNR in the pelvis and thigh, but this does not affect interpretability of images obtained at these stations. The temporal gain results in significantly increased interpretability as a result of less venous contamination in the calf station. iPAT MR angiography is superior to conventional MR angiography for peripheral imaging.

Adolescent↗
PubMed2006

Real-time magnetic resonance-guided placement of retrievable inferior vena cava filters: comparison with fluoroscopic guidance with use of in vitro and animal models.

PURPOSE: To compare the precision of magnetic resonance (MR)-guided versus fluoroscopy-guided placement of retrievable inferior vena cava (IVC) filters with use of real-time MR imaging strategies optimized for each device in an in vitro model and in an animal model. MATERIALS AND METHODS: Three different retrievable IVC filters were used in this study, including the Recovery, Günther Tulip, and OptEase devices. Experiments were performed on a 1.5 T-MR system with pre-release interactive MR software. For each device, high-resolution real-time MR imaging was optimized with use of steady-state free precession and fast low-angle shot sequences with radial and cartesian trajectories and varying flip angles (10 degrees -70 degrees ) and a frame rate of 2 per second. A custom-built IVC phantom was filled with dilute gadolinium contrast agent at a concentration of 0.05 mmol/L simulating a blood T1 of 8 msec and T2 of 6 msec. Signal intensities were measured in regions of interest at the filter, the IVC lumen, and the background. The contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were calculated. The sequence suited best for each device was chosen for in vitro filter placement in a custom-made IVC phantom. Each device was deployed five times each under MR and fluoroscopic guidance with use of identical techniques. Accuracy was measured as absolute deviation of the filter tip in millimeters from a target landing zone. Differences were assessed statistically with use of the paired t test. Each device was also placed in vivo in a swine model under MR guidance. RESULTS: All three IVC filters could be clearly identified and positioned under fluoroscopic and MR imaging control. A cartesian true fast imaging sequence with steady-state precession with a flip angle of 30 degrees or 50 degrees resulted in optimal SNR and CNR for all three filters. The Tulip filter created more susceptibility artifacts than the other two. Filter placement accuracy was similar with MR and fluoroscopy whether comparing devices individually (P=NS) or as a group (P=NS). The mean absolute differences between MR and fluoroscopy were 0.088 mm for the OptEase filter, 0.41 mm for the Bard Recovery filter, and 0.34 mm for the Günther Tulip filter. CONCLUSIONS: MR-guided placement of retrievable IVC filters is feasible and as accurate as fluoroscopy-guided placement in an in vitro model. With optimized sequences, real-time MR has the potential to develop as a reasonable alternative to fluoroscopy.

Animals↗
PubMed2006

Carotid artery calcification on CT may independently predict stroke risk.

OBJECTIVE: The purpose of our study was to quantitatively evaluate calcified atherosclerotic burden in the cervical carotid arteries using MDCT to determine the relationship of scores with luminal stenosis and symptomatology. MATERIALS AND METHODS: Calcium plaque volume was measured in 106 cervical carotid arteries (53 patients) using MDCT angiography. The study group included 32 asymptomatic patients (mean age, 70.2 +/- 8.7 [SD] years; 15 women, 17 men) and 21 patients with ischemic neurologic symptoms (69.6 +/- 12.9 years; eight women, 13 men). By vessel, there were 43 high-grade stenotic (> or = 60% by North American Symptomatic Carotid Endarterectomy Trial [NASCET] criteria), 15 moderate-grade stenotic (30-59%), and 44 mild-grade stenotic or normal (0-29%) vessels, with four excluded for prior carotid endarterectomy. Volume scores were calculated by summing the area of calcium in the common and extracranial internal carotid arteries on axial slices and multiplying by the slice increment. RESULTS: Controlling for cardiovascular risk factors and luminal stenosis, we found that scores were significantly related to the occurrence of symptoms (p = 0.003). Even with patient age as a covariant, patients with high-grade stenosis had significantly higher scores than those without high-grade disease (p = 0.004). Moreover, quantitative burden was associated with luminal stenosis on adjusted multivariate analysis (p = 0.034). The specificity and positive predictive value for high-grade luminal narrowing were notably lower on individual vessel analysis than on total score analysis, likely secondary to variability in vascular remodeling. CONCLUSION: Calcium scores in the cervical carotid arteries may represent an independent marker for luminal stenosis and ischemic symptoms. A prospective longitudinal study examining calcium levels and morbidity may be warranted to examine whether burden has a role in risk stratification.

Aged↗
PubMed2006

Surgical and endovascular repair of aortic coarctation: normal findings and appearance of complications on CT angiography and MR angiography.

OBJECTIVE: A variety of treatment options exist for aortic coarctation, both surgical and catheter-based. Knowledge of the normal radiologic appearance of these, as well as their typical complications, is essential for interpretation of CT and MR angiographic studies in these patients. CONCLUSION: CT and MR angiography are noninvasive techniques that are well suited to follow patients after coarctation repair.

Adult↗
PubMed2005

Magnetic resonance urography for the assessment of potential renal donors: comparison of the RARE technique with a low-dose gadolinium-enhanced magnetic resonance urography technique in the absence of pharmacological and mechanical intervention.

The aim of this study was to determine whether magnetic resonance urography without pharmacological (diuretic) stimulation and mechanical compression allows conclusive evaluation of the urinary system in potential renal donors. In 28 consecutive patients magnetic resonance urography (MRU) was performed on a 1.5-T system. Two techniques, rapid acquisition with relaxation enhancement (RARE) and a gadolinium (Gd)-enhanced 3D fast low angle shot (FLASH) sequence were compared in the absence of adjunctive measures. Two reviewers assessed image quality, presence of artifacts and completeness of visualization of the collecting systems and ureters. Among the 53 MR urograms, there was no difference in image quality and presence of artifacts between RARE and Gd-MRU. Despite high image quality, visualization of the urinary collecting system was insufficient. Continuous visualization from the collecting system to the distal ureter was demonstrated bilaterally in only 14% of the RARE and 26% of Gd-enhanced MR urograms, respectively. Overall, Gd-enhanced MRU was superior to the RARE technique in displaying the segments of the urinary collecting system, but this difference was not found to be statistically significant. Neither the RARE technique nor the gadolinium-enhanced MRU technique is accurate enough to allow the evaluation of the collecting system and ureters in potential renal donors in the absence of pharmacological intervention and compression.

Adult↗
PubMed2005

Accuracy of computed tomography attenuation values in the characterization of pleural fluid: an ROC study.

RATIONALE AND OBJECTIVES: To assess the accuracy of computed tomography (CT) in characterizing pleural fluid based on attenuation values. MATERIALS AND METHODS: Protocol was approved by the local institutional review board and informed consent was waived. We retrospectively analyzed 145 pleural effusions of 145 patients (mean/standard deviation age: 60.7/15.9 years; 69 females) who underwent CT of the thorax and diagnostic thoracentesis within 7 days of each other. Effusions were classified as transudates or exudates using laboratory markers based on Light's criteria. The mean Hounsfield units (HU) of an effusion was determined by a region of interest on the three slices with the greatest anteroposterior diameter. A receiver operating characteristic curve was constructed to determine threshold values for classification on the basis of mean HU and to examine overall accuracy, using the area under the curve (A(z)). RESULTS: Of the 101 exudates and 44 transudates, the mean attenuation of exudates (17.1 HU/standard deviation 4.4) was significantly higher than transudates (12.5 HU/6.3), (P < .001). There was a modest but significant positive relationship between mean HU and laboratory markers, with the strongest relationship with pleural/serum protein (r = 0.57, P < .001) and total pleural protein (r = 0.56, P < .001). The overall accuracy of attenuation values for identifying exudates was moderate, Az = 0.775, standard error = 0.039, with the largest limitation being the overlap with transudates in the 10-20 HU range, which constituted 66% (90/145) of the total effusions measured. CONCLUSION: Although the mean attenuation of exudates is significantly higher than transudates, the clinical use of CT numbers to characterize pleural fluid is not recommended, as their accuracy is only moderate. Moreover, there is a notable overlap in attenuation values between transudates and exudates for a majority of effusions.

Adolescent↗
PubMed2005

Percutaneous extraction of bilateral renal mycetomas in premature infant using mechanical thrombectomy device.

Although mycotic infections of the urinary system occur not infrequently, obstruction of the upper urinary tract because of mycetomas or fungus balls is exceedingly rare. Treatment consists of antifungal treatment and appropriate urinary drainage. In cases resistant to treatment with external drainage and chemotherapy, open surgery is typically performed to remove the mycetoma. However, this can also be achieved percutaneously using mechanical thrombectomy devices, as shown in this case of a 4-month-old infant presenting with renal failure due to bilateral obstructing mycetomas.

Acute Kidney Injury↗
PubMed2005

Subintimal arterial flossing with antegrade-retrograde intervention (SAFARI) for subintimal recanalization to treat chronic critical limb ischemia.

PURPOSE: To describe the technique of subintimal arterial flossing with antegrade-retrograde intervention (SAFARI) to improve technical success for the performance of subintimal recanalization when there is failure to reenter the distal true lumen or when there is a limited segment of patent distal target artery available for reentry. MATERIALS AND METHODS: Subintimal recanalization was attempted in an antegrade direction in all patients. If reentry into the distal true lumen was unsuccessful or a short segment of target artery was present, retrograde access was obtained in the distal target artery (popliteal, anterior tibial/dorsalis pedis, or posterior tibial) and a retrograde subintimal channel was created. A guide wire was used to connect the retrograde and antegrade subintimal channels simultaneously to create a "flossing" guide wire. The subintimal tract was dilated with balloon angioplasty with or without stent implantation. Limb salvage, amputation-free survival, and survival rates over time were determined. RESULTS: The SAFARI technique resulted in successful subintimal recanalization creating straight-line flow to the foot in all 21 limbs in 20 patients in which the technique was attempted. Antegrade-retrograde access was performed with the femoral artery and the following vessels: popliteal, n = 11; anterior tibial/dorsalis pedis, n = 10; and posterior tibial, n = 2 (two limbs involved multiple accesses). All procedures were successful. The limb salvage rate with SAFARI was 90% (95% CI, 74%-100%) at 6 months. CONCLUSIONS: The SAFARI technique can be useful for completing subintimal recanalization when there is failure to reenter the distal true lumen from an antegrade approach or when there is limited distal target artery available for reentry. The SAFARI technique improves technical success in the performance of subintimal recanalization. Limb salvage rates are comparable to those with antegrade subintimal recanalization.

Aged↗
PubMed2005

Renal angioplasty and stent placement with distal protection: preliminary experience with the FilterWire EX.

Percutaneous transluminal renal angioplasty and stent placement with use of a coronary protection device was performed in a total of four patients with hypertension (n = 4) and/or renal insufficiency (n = 3) referred for revascularization of five renal arteries. Renal revascularization was successful in all five renal arteries (100%), but renal revascularization under protection by the FilterWire EX was achieved in only three of five renal arteries (60%). In one of these three, only a suboptimal seal was achieved between the vessel wall and the filter basket. Nevertheless, use of the device was safe and fibrin and/or cholesterol fragments were retrieved from three renal arteries. The FilterWire EX needs to be modified for the renal circulation to achieve the full theoretical advantages of these systems in this vascular bed.

Aged↗
PubMed2005

Pulmonary embolism: comprehensive evaluation with MR ventilation and perfusion scanning with hyperpolarized helium-3, arterial spin tagging, and contrast-enhanced MRA.

PURPOSE: Development of a comprehensive magnetic resonance (MR) examination consisting of MR angiography (MRA) and MR ventilation and perfusion (MR V/Q) scan for the detection of pulmonary emboli (PE) and assessment of the technique in a rabbit model. MATERIALS AND METHODS: Reversible PE was induced by inflating a non-detachable silicon balloon in the left pulmonary artery of five New Zealand White rabbits. MR V/Q scans were obtained prior to, during, and after balloon deflation. MRA was performed during balloon inflation. MR ventilation imaging was performed after the inhalation of hyperpolarized helium-3. MR perfusion imaging was performed with Flow-sensitive Alternating Inversion Recovery with an Extra Radiofrequency pulse technique (FAIRER). High-resolution contrast-enhanced MR pulmonary angiography was used to confirm the occlusion of the pulmonary artery. All imaging was performed on a 1.5-T whole body scanner with broadband capabilities. RESULTS: High-resolution ventilation images of the lungs were obtained. No ventilation defects were detected before, during, or after resolution of simulated PE. FAIRER imaging allowed visualization of pulmonary perfusion. No perfusion defects were detected prior to balloon inflation. During balloon inflation (PE), there was decreased perfusion in the left lower lobe. After reversal of the PE, there was improved perfusion to the left lower lobe. In analogy to nuclear medicine techniques, acute PE produced a mismatched defect in the MR V/Q scan. MRA verified the occlusive filling defect in the left pulmonary artery. CONCLUSION: High-resolution MRA and MR V/Q imaging of the lung is feasible and allows comprehensive assessment of pulmonary embolism in one imaging session.

Animals↗
PubMed2005

Type 1 collagen as an endovascular stent-graft material for small-diameter vessels: a biocompatibility study.

PURPOSE: To compare patency rates and degrees of neointimal hyperplasia between bovine type 1 collagen stent-grafts and uncovered control stents in small-diameter vessels (< or =4 mm). MATERIALS AND METHODS: Uncovered stainless-steel, balloon-expandable stents (n = 5) and type 1 collagen stent-grafts (n = 6) were implanted via the femoral arteries with use of 4-mm balloon catheters into the abdominal aorta of New Zealand White rabbits. Ten animals were available for follow-up. Subjects were followed for 1 month (three uncovered stents; three collagen stent-grafts) or 4 months (two uncovered stents; two collagen stent-grafts). Angiography was performed before animal sacrifice and luminal compromise was compared between groups. Histologic and immunohistochemical analysis was performed to determine presence of neointima and neointimal thickness and area; these parameters were also compared between groups. RESULTS: All stents and stent-grafts remained patent at both time points. Luminal compromise was not detectable angiographically in any subject. Maximum neointimal thickness was less than 5 mum for all subjects. Neointimal thickness and area were not statistically significantly different between groups. CONCLUSIONS: Type 1 collagen stent-grafts demonstrate excellent hemocompatibility and biocompatibility in small-diameter vessels in rabbits.

Animals↗
PubMed2005

Contrast-enhanced MR angiography at 1.5 T after implantation of platinum stents: in vitro and in vivo comparison with conventional stent designs.

OBJECTIVE: The objective of our study was to evaluate the in vitro and in vivo 3D contrast-enhanced MR angiography characteristics of a new platinum-based balloon-expandable stent system and compare this system with a variety of competing metallic stents. MATERIALS AND METHODS: All experiments were performed on 1.5-T scanners. In vitro experiments were performed using 10 stents implanted into a custom-built phantom. Different orientations of the stents along the magnetic field and multiple flip angles were examined. In addition, 19 patients underwent contrast-enhanced MR angiography after the implantation of 36 stents, including four patients with six platinum stents. Angiographic correlation was available for all 19 patients, and luminal patency and stent-induced artifacts were assessed quantitatively. RESULTS: Of the tested balloon-expandable stents, only the platinum-based stents created artifact causing luminal narrowing of 30% or less. All other balloon-expandable stents induced larger artifacts that resulted in higher degrees of narrowing. Thus, if patent, the platinum-based stents allow significant in-stent stenosis to be ruled out reliably. Selected nitinol- or tantalum-based self-expandable stents also are suitable in this regard. CONCLUSION: Of the tested devices, platinum-based stents are the only type of currently available balloon-expandable stent that creates 30% or less artifact-induced apparent stenosis and thus are suitable for MR angiography.

Aged↗