M. K. Stehling

Single-shot T1- and T2-weighted magnetic resonance imaging of the heart with black blood: preliminary experience

AbstractPurpose: To implement and evaluate two robust methods for T1-and T2-weighted snapshot imaging of the heart with data acquisition within a single heart beat and suppression of blood signal. Methods: Both Tl-and T2-weighted diastolic images of the heart can be obtained with half Fourier single-shot turbo spin echo (HASTE) and turbo fast low-angle shot (turboFLASH) sequences, respectively, in less than 350 ms. Signal from flowing blood in the ventricles and large vessels can be suppressed by a preceding inversion recovery preparing pulse pair (PRESTO). Fifteen volunteers and five patients have been evaluated quantitatively for signal-to-noise ratio (SNR) contrast-to-noise ratio (CNR) and flow void and qualitatively for image quality, artifacts, and black-blood effect. Results: Both PRESTO-HASTE and PRESTO-turboFLASH achieved consistently good image quality and blood signal suppression. In contrast to gradient-echo (GRE) echo-planar imaging techniques, (EPI) HASTE and turboFLASH are much less sensitive to local susceptibility differences in the thorax, resulting in a more robust imaging technique without the need for time-consuming system tuning. Compared to standard spin-echo sequences with cardiac triggering, HASTE and turboFLASH have significantly shorter image acquisition times and are not vulnerable to respiratory motion artifacts. Conclusion: PRESTO-HASTE and PRESTO-turboFLASH constitute suitable methods for fast and high-quality cardiac magnetic resonance imaging (MRI).

Oxygen-induced MR signal changes in murine tumors

Breathing of 100% oxygen was used to challenge vascular autoregulation in 14 mice with either osteosarcomas (n = 6) or mammary carcinomas (n = 8). Reproducible and statistically significant signal intensity changes of -29 +/- 6% to +35 +/- 3% were observed on heavily T2*-weighted images in the tumors during the oxygen challenge. No significant changes were observed in muscle. For the mammary carcinomas a higher percentage of tumor voxels showed significant signal-intensity decrease (31 +/- 8%) compared to the percentage of voxels showing a signal-intensity increase (22 +/- 3%). In contrast, for the osteosarcomas, a higher percentage of tumor voxels showed signal-intensity increase (52 +/- 9%) compared to the percentage of voxels showing signal-intensity decrease (27 +/- 9%). The regional distribution of these signal intensity changes did not correlate with the signal pattern on T1-, T2-,and T2*-weighted and Gd-DTPA enhanced images acquired without breathing 100% oxygen. Most likely, the signal intensity changes represented the inability of the tumors neovascularization for autoregulation during the oxygen challenge, particularly in hypoxic regions. Although further investigation is needed, the findings that malignant tumor tissue showed signal intensity changes, whereas normal muscle tissue did not, suggests that this technique may prove useful in distinguishing benign from malignant tissue.

Gadolinium-enhanced magnetic resonance angiography of the pelvis in patients with erectile impotence.

This study evaluted the potential of contrast-enhanced digital-subtraction magnetic resonance angiography (CE-DS-MRA) for noninvasive angiographic delineation of the arterial supply of the penis in patients with erectile dysfunction. After induction of an erection with prostaglandin E, a three-dimensional fast imaging with steady-state precision (FISP) sequence with TE of 1.8–2 milliseconds, TR of 4.4–5 milliseconds, and flip angle of 40°–60° was used to obtain high-resolution angiograms of the pelvis and penis during the injection of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) 0.3 mmol/kg body weight, within 30–50 seconds. DS maximum intensity projections (MIPs) and multiplanar reconstructions (MPRs) were compared with clinical work-up and directional Doppler ultrasound in 11 patients. In all 11 patients (100%), the arterial supply of the penis could be delineated from the aortic bifurcation via the iliac and internal pudendal arteries to the dorsal and deep penile arteries. Of the 22 internal pudendal arteries, 6 (27%) were occluded on CE-DS-MRA and 5 (23%) had stenoses, of which 4 (18%) were greater than 50%. In 7 patients (64%) good correlation between CE-DS-MRA and clinical findings and/or Doppler ultrasound was found; in 2 patients (18%), the correlation was moderate, and in 2 patients (18%) results were discrepant. In 6 patients (55%), MRA provided additional information to the clinical and Doppler ultrasound work-up. CE-DS-MRA can delineate small sessels such as the internal pudendal and penile arteries and thus has the potential to become a noninvasive angiography method in the work-up of erectile impotence.

MRT-Monitoring vor, während und nach der interstitiellen laserinduzierten Thermotherapie der benignen ProstatahyperplasieErste klinische Erfahrungen

ZusammenfassungDie Magnetresonanztomographie (MRT) ermöglicht eine nicht-invasive Bestimmung von Temperaturänderungen in Proben und lebenden Geweben. Beim Monitoring der interstitiellen laserinduzierten Thermotherapie (LITT) während der Patientenbehandlung werden derzeit vor allem relativ T1-gewichtete FLASH-Sequenzen eingesetzt. In eigenen Untersuchungen bei Patienten mit benigner Prostatahyperplasie konnte mit T1-gewichteten FLASH-Sequenzen eine mit zunehmender interstitieller Energiedeposition im Prostatagewebe durch einen Nd: YAG-Laser proportional deutlich abnehmende Signalintensität um die Laserlichtleiterspitze nachgewiesen werden. Das MR-Signal nahm dabei den gleichen Verlauf wie in Proben bovinen Prostata- und Samenblasengewebes, die unter gleichen Bedingungen behandelt wurden, und kehrte nach Bestrahlungsende zur Ausgangsintensität zurück. Während die Ränder der Laserläsionsareale während der LITT in den FLASH-Sequenzen nicht sicher abgegrenzt werden konnten, waren die Läsionen unmittelbar nach LITT in kontrastverstärkten T1-gewichteten Spinechoaufnahmen als signalarme Areale klar vom signalreichen, hyperämischen Umgebungsgewebe abgrenzbar. Die Größe der gesamten Prostata und der Innendrüse konnte in T2-gewichteten TSE-Aufnahmen mit einer Reproduzierbarkeit von + / − 3,2–4,7 % bestimmt werden. Bei Nachuntersuchungen an 8 Patienten über 6–12 Monate nahmen die Volumina von Gesamt- und Innendrüse im Durchschnitt um jeweils 20 % ab. Dabei korrelierte die Volumenänderung 2–3 Wochen, 6–8 Wochen und 6–12 Monate nach Therapie stets mit Koeffizienten von 0,85–0,90 mit der Entwicklung der Laserläsionsgröße. SummaryPurpose: To assess the clinical value of MRI in patients with benign prostatic hyperplasia (BPH) before, during, and after interstitial laser-induced thermotherapy (LITT) of the prostate. Methods: Ten patients with symptomatic BPH had MRI examinations of the prostate 48 h before and after LITT. Online monitoring with MRI at 1.5 T of interstitial Nd:YAG laser energy deposition in the prostate was performed in two patients, repeating a T1-weighted FLASH sequence (TR 100 ms, TE 5 ms, flip angle 90 °) every 20 s. Follow-up MRI examinations 2–3 weeks, 6–8 weeks, and 6–12 months after LITT were carried out in eight patients, using T2-weighted FSE images and contrast-enhanced T1-weighted SE images. Results: The prostate was well delineated in all patients on T2-weighted FSE images, with a rather homogeneous peripheral gland and an inhomogeneous central gland. Volume measurements yielded reproducibilities of 3.2 %–4.7 %. Signal intensity in the FLASH sequence decreased during LITT, both in the prostate in vivo and in specimens of bovine prostate and seminal vesicles in vitro, with signal developments running in parallel. Areas of energy deposition and signal alteration were not sharply delineated. The latter margin of the laser-induced lesions could not be predicted from the FLASH images, while the tip of the laser fibre was easily recognized. Contrast-enhanced T1-weighted MR images immediately after LITT clearly demarcated low signal intensity laser lesions from high signal intensity surrounding prostate tissue. Follow-up examinations showed a decrease of 20 % of prostate volume over a period of 6–12 months after LITT. Correlation between prostate volume development and lesion volume alteration was 0.85–0.90 (P = 0.002–0.007) at all follow-up times. Conclusions: MRI allows rather precise recognition of intraprostatic alterations after LITT, including volume changes over a period of up to 1 year after therapy that can be predicted immediately after LITT. While laser energy deposition in the prostate can be monitored by MRI with T1-weighted FLASH sequences as a function of temperature alteration, it is not possible to determine the lesion margins immediately from the FLASH images. Online temperature development map generation will be necessary to influence ongoing LITT procedures with MRI.

Magnetic resonance imaging of the female pelvis. New circularly polarized body array coil versus standard body coil.

RATIONALE AND OBJECTIVES The authors compare the value of a new circularly polarized body array coil (BAC) system with a standard body coil (BC) for high-resolution magnetic resonance imaging of the female pelvis. METHODS Twenty patients with cervical cancer were examined with a BC and BAC. Imaging parameters were kept constant (sagittal T2-weighted turbo spin-echo: repetition time = 4000 mseconds; effective echo time = 99 mseconds; 160 x 160 mm field of view; 256 x 256 matrix; 0.63 x 0.63 mm pixel size; 4-mm slice thickness). Images were scored for lesion-to-organ delineation and overall image quality/ artifacts using a scale from 5 to 1 (excellent to poor). Signal-to-noise (S/N) ratios for different tissues (tumor, uterus, vagina, rectum, muscle, and fat) as well as contrast-to-noise (C/N) ratios between tumor and (1) uterus, (2) vagina, and (3) rectum were calculated. Magnetic resonance tumor staging was performed according to the International Federation of Gynecology and Obstetrics (FIGO) classification. RESULTS Using the BAC, S/N and C/N ratios increased significantly compared with the BC (S/N: 2.7-3.4-fold increase for all organs evaluated, P < 0.001: C/N: tumor versus uterus 2.4-fold, P < 0.01; tumor versus vagina 6.1-fold, P < 0.001; tumor versus rectum 3.1-fold, P < 0.01). This resulted in an improved overall image quality (average ratings: BAC-4.3 points; BC-2.6 points; P < 0.001). Lesion-to-organ delineation (average ratings: BAC 4.3-4.1 points, BC 3.5-2.7 points for all organs evaluated; P < 0.001) was increased noticeably on BAC images. No significant difference was found for staging accuracy. CONCLUSIONS Circularly polarized BAC provide superior S/N and C/N ratios and improve lesion conspicuity compared with standard BC.

Gadolinium-enhanced magnetic resonance angiography of the abdominal vessels

SummaryContrast enhanced (CE) magnetic resonance angiography (MRA) provides high resolution angiograms within 20–40 sec. The technique is based on the acquisition of heavily T1-weighted threedimensional (3D) gradient-echo data sets (FISP) with ultrashort echo- (< 2 ms) and repetition times (< 5 ms) during the arterial phase of an intravenously injected bolus of a T1-shortening agent such as Gd-DTPA. For MR-angiography of abdominal vessels CE-MRA is better suited than “time-of-flight” (TOF) and phase-contrast (PC) MRA because motional artifacts can be obviated with breath-held acquisitions. We have optimised the technique and evaluated its potential for angiography of the abdominal aorta and its branches as well as the portal vein and its tributaries. Whilst CE-MRA provides reliable diagnostic accuracy in the aorta and the proximal sections of its branches, small peripheral arteries cannot be assessed accurately. The portal vein and its tributaries can often be depicted better with CE-MRA than with conventional angiography but, like conventional angiography, CE-MRA is hampered by slow and reversed flow, conditions under which TOF or “true FISP” MRA may perform bst. We have also investigated FLASH-echo-planar imaging (EPI) hybrid techniques, a further technical development which due to shorter acquisition times of 12–15 sec. allows semi-dynamic imaging of the arterial and venous phase and provide better vessel contrast due to the use of fat-suppression.ZusammenfassungDie kontrastmittelverstärkte (CE, „contrast enhanced“) Magnetresonanzangiographie (MRA) liefert hochaufgelöste Angiographien innerhalb von 20–40 s. Die Technik basiert auf der Akquisition stark T1-gewichteter dreidimensionaler (3D) Gradientenechodatensätze (FISP) mit ultrakurzen Echo- (< 2 ms) und Repetitionszeiten (< 5 ms) während der arteriellen Phase eines intravenös injezierten Bolus eines T1-verkürzenden Kontrastmittels wie z. B. Gd-DTPA. Für die Angiographie der Abdominalgefäße ist die CE-MRA der „time-of-flight“ (TOF) und Phasenkontrast (PC) MRA überlegen, da Bewegungsartefakte durch Aufnahmen im Atemstillstand fast vollständig vermieden werden. Wir haben die Technik der CE-MRA optimiert und ihr Potential für die Angiographie der Bauchaorta und ihrer Äste als auch des Pfortaderkreislaufs evaluiert. Während die CE-MRA im Bereich der Aorta und der proximalen Abschnitte ihrer Äste zuverlässige diagnostische Informationen liefert, können kleine, periphere Gefäße nicht zuverlässig beurteilt werden. Der Pfortaderkreislauf kann mit der CE-MRA oft besser als mit der konventionellen Angiographie beurteilt werden, ist aber, wie auch die konventionelle Angiographie, durch langsamen Fluß oder Flußumkehr behindert, Umstände, unter denen die TOF oder „true-FISP“ MRA die besten Ergebnisse liefern kann. Wir haben darüber hinaus FLASH-Echo-Planar-Imaging (EPI) Hybridtechniken untersucht, eine technische Weiterentwicklung, die auf Grund der kürzeren Aufnahmezeiten von 12–15 s die semidynamische Abbildung der arteriellen und venösen Phase ermöglicht und durch den Einsatz von Fettunterdrückung einen verbesserten Gefäßkontrast liefert.

Choledocholithiasis after Billroth II surgery: MR cholangiographic diagnosis

Abstract. In this case of choledocholithiasis in a patient with previous Billroth-II surgery and cholecystectomy we demonstrate the advantages of a heavily T2-weighted half-Fourier turbo-spin-echo (HASTE) sequence. This technique allows thin-slice snapshot imaging with 1.4 s per slice eliminating motion artifacts and still has the necessary heavy T2-weighting to depict biliary fluid with high contrast. In the presented case endoscopic retrograde cholangiography (ERCP) could not be performed prior to MRI due to technical problems. In a second attempt, ERCP was successful and a common bile duct stone as diagnosed by MRI before could be removed. We conclude that HASTE snapshot MR cholangiography can be used as a clinically valuable tool when other noninvasive methods are not diagnostic.

Effects of partial volume and phase shift between fat and water in gradient-echo magnetic resonance-mammography

The signal modulations caused by partial volume effect and phase shift between fat and water signal in gradient-echo magnetic resonance mammography (GRE MR-mammography) have been calculated. Based on this, the theoretical sensitivity and specificity of GRE MR-mammography has been investigated considering different evaluation methods for the gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA)-based signal enhancement. The results show that both in- and out-of-phase sequences suffer from partial volume effects in voxels that contain both fat and water. This can decrease sensitivity to Gd-DTPA uptake in small, fat-embedded lesions or in pathology that contains fat interspersed histologically. Additionally, out-of-phase sequences can suffer from phase cancellation effects that can further decrease their sensitivity to Gd-DTPA uptake. In the worst case signal can actually decrease during Gd-DTPA influx. Determination of enhancement relative to the baseline value can decrease the specificity of GRE MR-mammography in the out-of-phase condition and decrease the sensitivity in the in-phase condition. These effects are less pronounced when enhancement is calculated relative to fat. These effects need to be understood since Gd-DTPA uptake is the prime indicator of malignancy in MR-mammography.

Echo planar imaging's impact on modern diagnostic MR-imaging: general principles and historic facts.

Echo-planar imaging (EPI) [1,2] invented in 1976/77 by Sir Peter Mansfield, only 4 years after the conception of magnetic resonance imaging [3,4], has been one of the most important driving forces in the development of modern magnetic resonance imaging (MRI). Contrary to widespread belief EPI is more than a pulse sequence to obtain MR-images within a fraction of a second (typically in 50-100 ms). EPI is a fundamental data acquisition strategy [5]: instead of acquiring single NMR echoes repeatedly to form an image, as in other MR techniques, EPI acquires multiple, progressively phase-encoded NMR echoes and, in its extreme form of implementation, all the raw data to generate an image in a single acquisition. In this paper we will review how this efficient, generally applicable data acquisition principle has influenced the development of modern diagnostic MRI. It will be shown that most modern MR-techniques, such as fast spin-echo, RARE, HASTE, GRASE, are direct derivatives of EPI and that all modern MR techniques have profited from the technological developments spurred by EPI.

CT-Subtraktionsangiographie (CTSA) : Ergebnisse mit einem automatisierten elastischen Subtraktionsalgorithmus

ZusammenfassungEs wurde eine Methode zur überlagerungsfreien Darstellung von Gefäßen mittels der CT-Angiographie (CTA) entwickelt und erprobt. Dazu wurde ein automatisierter, sog. „elastischer“ digitaler Subtraktionsalgorithmus entwickelt, der es ermöglicht, einen Spiral-CT-Datensatz ohne Kontrastmittel von einem solchen mit Kontrastmittel artefaktfrei zu subtrahieren. Der „elastische“ Subtraktionsalgorithmus korrigiert stochastische, transmissionsbedingte und durch Bewegung verursachte Inkongruenzen zwischen den beiden zu subtrahierenden Datensätzen und ist somit der einfachen digitalen Subtraktion überlegen. Bisher wurde die CT-Subtraktionsangiographie (CTSA) an 7 Patienten im Bereich der Hals- und intrakraniellen Gefäße erprobt. Der „elastische“ Subtraktionsalgorithmus war bei der Beurteilung von Bildqualität und -artefakten in allen Fällen und statistisch signifikant besser als die einfache digitale Subtraktion. Die „elastische“ CTSA ermöglicht eine automatisierte Trennung von ossären Strukturen und Gefäßen und erleichtert somit die überlagerungsfreie, räumliche und selektive Darstellung der Hals- und intrakraniellen Gefäße.SummaryPurpose: To develop and implement a method to obtain digital subtraction (DS) spiral computed tomography angiograms (SCTA) in order to avoid superimposition of bony structures and vascular calcifications on SCTA maximum intensity projections (MIPs) and shaded surface display (SSD). Method: Two SCTA data sets, one before and one during the injection of a contrast agent bolus, were obtained with identical scan parameters. Since ordinary subtraction of the two data sets fails to reliably separate bones and calcifications from the vascular lumen because of motion, a so-called elastic subtraction procedure was designed to correct 3D misregistration between the two data sets. It automatically accommodates for local position changes between baseline and contrast images, including regionally inconsistent non-linear displacements and arbitrary rotations. This method was tested in seven patients and evaluated against ordinary DS in terms of image quality and artifacts. Results: In all patients “elastic” CTSA proved superior to ordinary DS. It provides automated and reliable separation of vessels from bones and calcifications. This improves the delineation of vessels in the neck and the skull base and of intracranial vessels. DS-SCTA facilitates MIPs and SSD without artifacts introduced by thresholding. Conclusion: Elastic DS-SCTA is a robust method for automated unmasking of vessels from bones and warrants clinical trials and comparison with MR- and conventional angiography.