Biomedical subjects

Michael Fenchel

Publications and source records attributed to Michael Fenchel.

24 records · Page 2Linked to original sources

PubMed2005

Assessment of minimally invasive direct coronary artery bypass grafting of the left internal thoracic artery by means of magnetic resonance imaging.

OBJECTIVES: We sought to evaluate graft patency, flow, and flow reserve in patients with minimally invasive direct coronary artery bypass surgery of internal thoracic artery grafts by a combined magnetic resonance protocol with a phase-contrast technique and magnetic resonance angiography. METHODS: At 1.5 T (Magnetom Sonata, Siemens), 30 symptomatic patients with 30 left internal thoracic artery grafts were examined 6 years after minimally invasive surgical intervention. Navigator-gated magnetic resonance angiography and contrast-enhanced FLASH-3D magnetic resonance angiography (0.2 mmol gadopentate-diethylene triamine pentetic acid [Gd-DTPA]/kg body weight) was used to assess bypass patency. Phase-contrast flow measurements with retrospective gating were performed in the internal thoracic artery grafts at rest and after stress induction with dipyridamole (0.57 mg/kg body weight). Graft patency was evaluated by means of multidetector computed tomography (Sensation 16, Siemens). RESULTS: Internal thoracic artery grafts were occluded in 5 of 30 patients. In 6 patients the anastomosis to the left anterior descending artery was highly stenotic (>70 % ) at multidetector computed tomography. In patients with regular grafts (multidetector computed tomography), a significant improvement of graft flow ( P < .001) and diastolic/systolic peak velocity ratio ( P < .001) after stress induction was detected. Magnetic resonance angiography combined with flow reserve measurements could differentiate between occluded-stenotic and regular minimally invasive direct coronary artery bypass grafts. CONCLUSIONS: Magnetic resonance imaging allows a combined assessment of bypass patency and flow with flow reserve in patients after the minimally invasive direct coronary artery bypass operation. The protocol of this study might be applicable for the evaluation of graft status in symptomatic patients after revascularization.

Aged↗

PubMed2005

Fast whole-body assessment of metastatic disease using a novel magnetic resonance imaging system: initial experiences.

OBJECTIVE: The objective of this study was to investigate the clinical use of a novel whole-body magnetic resonance imaging (MRI) system for comprehensive assessment of tumor spread in clinical routine. MATERIAL AND METHODS: Sixty-five patients with different tumors with known metastatic disease and 6 healthy volunteers were included. High-resolution MRI from head to toe was performed using multiple phased-array surface coil elements, 24 independent receiver channels, and an integrated parallel acquisition technique (iPAT). A total room time of less than 60 minutes was required. Whole-body MRI and conventional spiral computed tomography (CT) were independently evaluated and compared in terms of feasibility, location/number of detected metastases, and therapeutic relevance. RESULTS: Whole-body MRI was successfully performed in 68 of 71 subjects. Compared with CT, more metastases were detected by MRI in 11 of 63 patients (17%), particularly in brain, liver, spleen, lymph nodes, bone marrow, muscle, and subcutaneous fat tissue. According to these findings, therapy had to be modified in 6 of 63 patients (10%). CONCLUSIONS: High-resolution whole-body MRI is feasible in clinical routine within 1 single examination and offers great potential for fast assessment of individual tumor spread and total tumor burden.

Adolescent↗

PubMed2005

Detection of regional myocardial perfusion deficit using rest and stress perfusion MRI: a feasibility study.

OBJECTIVE: Providing high temporal and spatial resolution, perfusion MRI is an attractive alternative to traditional radionuclide methods like SPECT and PET. Although first-pass perfusion MRI examinations have gained increasing attention during the past years, this technique still exhibits relatively low signal-to-noise ratio and cardiac coverage. Previous studies have suggested that refocused gradient sequence technology (e.g., true fast imaging with steady-state precession [FISP]) should improve perfusion MRI examinations. The aim of this study was to assess myocardial perfusion deficits in patients with proven coronary artery disease using a saturation recovery true FISP perfusion sequence. SUBJECTS AND METHODS: Rest and stress perfusion MRI studies were performed in 22 patients with coronary artery disease at 1.5 T using a multislice saturation recovery true FISP sequence after the bolus injection of 0.025 mmol/kg of body weight of gadopentetate dimeglumine. The myocardium of each slice was divided into 12 radial segments with subdivision into subendocardial and subepicardial subregions. Myocardial perfusion was assessed semiquantitatively and independently for each subregion. The standard of reference for myocardial perfusion was SPECT. Delayed enhancement images were acquired after the injection of 0.15 mmol/kg of body weight of gadopentetate dimeglumine. RESULTS: Sensitivity and specificity of perfusion MRI examinations for the detection of perfusion deficits were 81% and 89%, respectively, for the semiquantitative perfusion parameter upslope and 78% and 86% for the parameter peak signal intensity. More specifically, rest perfusion examinations were able to detect areas of infarction, whereas stress examinations increased the perfusion differences between normal and ischemic myocardial areas. Excellent correlation was observed between rest perfusion and late enhancement findings (r = 0.90). CONCLUSION: In patients with single-vessel coronary artery disease, perfusion deficits can reliably be detected using a saturation recovery true FISP sequence. Semiquantitative perfusion parameters upslope and peak signal intensity yielded similar results.

Adult↗

PubMed2004

Multislice first-pass myocardial perfusion imaging: Comparison of saturation recovery (SR)-TrueFISP-two-dimensional (2D) and SR-TurboFLASH-2D pulse sequences.

PURPOSE: To compare signal-to-noise ratio (SNR), contrast-to-noise (CNR) ratio, and diagnostic accuracy of a newly developed saturation recovery (SR)-TrueFISP-two-dimensional (2D) sequence with an SR-TurboFLASH-2D sequence. MATERIALS AND METHODS: In seven healthy subjects and nine patients with coronary artery disease (CAD), contrast-enhanced perfusion imaging (with Gd-DTPA) was performed with SR-TrueFISP and SR-TurboFLASH sequences. Hypoperfused areas were assessed qualitatively (scale = 0-4). Furthermore, SNR and CNR were calculated and semiquantitative perfusion parameters were determined from signal intensity (SI) time curves. Standard of reference for patient studies was single-photon emission computer tomography (SPECT) and angiography. RESULTS: The perception of perfusion deficits was superior in TrueFISP images (2.6 +/- 1.0) than in TurboFLASH (1.4 +/- 0.6) (P < 0.001). Phantom measurements yielded increased SNR (143 +/- 34%) and CNR (158 +/- 64%) values for TrueFISP. In patient/volunteer studies SNR was 61% to 100% higher and signal enhancement was 110% to 115% higher with TrueFISP than with TurboFLASH. Qualitative and semiquantitative assessment of perfusion defects yielded higher sensitivities for detection of perfusion defects with TrueFISP (68% to 78%) than with TurboFLASH (44% to 59%). CONCLUSION: SR-TrueFISP-2D perfusion imaging provides superior SNR and CNR than TurboFLASH imaging. Moreover, the dynamic range of SIs was found to be higher with TrueFISP, resulting in an increased sensitivity for detection of perfusion defects.

Adult↗

PubMed2004

Semiquantitative assessment of myocardial perfusion using magnetic resonance imaging: evaluation of appropriate thresholds and segmentation models.

RATIONALE AND OBJECTIVES: The aim of the study was to determine optimal thresholds for semiquantitative perfusion parameters and to evaluate the influence of different segmentation models in detecting malperfused regions. MATERIAL AND METHODS: In 6 healthy subjects and 13 patients with coronary artery disease, contrast-enhanced first-pass perfusion imaging was performed using a SR-TrueFISP-sequence. Thresholds for semiquantitative parameters were established, and different segmentation models of the left ventricular myocardium were tested. The standard of reference for patient studies was single photon emission computed tomography. RESULTS: Optimal thresholds were determined in healthy subjects for the perfusion parameters upslope, AUC, and peak SI of mv-0.5*std, mv-1.5*std, and mv-1.0*std, respectively. Using the optimal threshold for each parameter/segmentation combination sensitivities and specificities of stress studies were between 66% and 93% and 77% and 92%, respectively. Subdivision of radial segments into subendo/subepicardial segments increased sensitivities for perfusion deficits. CONCLUSIONS: Subdivision of radial myocardial segments is essential in analysis of magnetic resonance first-pass perfusion series. Semiquantitative perfusion parameters possess different sensitivities for the detection of perfusion deficits.

Adult↗

PubMed2003

Scimitar syndrome: morphological diagnosis and assessment of hemodynamic significance by magnetic resonance imaging.

Scimitar syndrome has a variable presentation depending on the age at which the diagnosis is made. We report a case of a young woman (age 18 years) with suspected right pulmonary hypoplasia in whom a scimitar syndrome was diagnosed. Using MRI morphological findings and hemodynamic significance of the syndrome were assessed. Left-to-right shunt was calculated from blood flow measurements performed in the ascending aorta, the main pulmonary artery, and the aberrant scimitar vein.

Adolescent↗