Evaluation and clinical quantification of neoplastic lesions and physiological structures in TOF-PET/MRI and non-TOF/MRI - a pilot study

PURPOSE

To clinically assess a new PET/MRI technology in which the PET--component features a new PET-- detector and time--of--flight (TOF) technology. Thus, we compared SUVmax/mean of neoplastic lesions and physiological structures between TOF-- and non--TOF--PET/MRI imaging. We qualitatively evaluated image quality derived from TOF-PET/MRI, non--TOF--PET/MRI reconstruction and FDG--PET/CT. Lastly we did clinical measurements to evaluate the PET-- detector sensitivity in order to better understand the background of our clinical results.

MATERIALS AND METHODS

Twenty--seven oncological patients were prospectively enrolled and evaluated with FDG-PET/CT and PET/MRI (15 M/ 12 F; mean age 56 ±10 y). Time between injection and PET/CT was 62.4 ±7.6 min, consecutive start of imaging of PET/MRI was 104.6 min±18.2 after injection. To assess the differences between TOF and non--TOF, all PET--images of the PET/MRI were reconstructed twice -with and without TOF. To compare lesion and tissue characterization between both reconstructions, malignant lesions as well as physiological structures were compared. Furthermore, PET image quality, artifacts, image sharpness, noise and lesion detectability were assessed as well. Count rates between both systems were also compared.

RESULTS

All malignant lesions and the majority of physiologic tissue (except the subcutaneous fat, spleen and blood pool) showed a good correlation concerning SUV (max and mean) measurements between PET/CT, non--TOF and TOF reconstructions. The general image quality was rated statistically significant superior in non--TOF (p<0.001) and TOF-reconstruction in PET/MRI (p<0.01) compared to PET/CT. Furthermore, TOF--PET/MRI was rated superior concerning image quality (p<0.05) compared to non--TOF PET/MRI. The ratio of emitted/received events between both systems (PET/CT and PET/MRI) was 2.78.

CONCLUSIONS

PET/MRI with TOF is reliable concerning SUV quantification and image quality. The technical promise of an improved sensitivity of the new PET--detector in this PET/MRI device could be confirmed in a clinical setting.

Advanced modelled iterative reconstruction for abdominal CT: qualitative and quantitative evaluation

AIM

To determine qualitative and quantitative image-quality parameters in abdominal imaging using advanced modelled iterative reconstruction (ADMIRE) with third-generation dual-source 192 section CT.

MATERIALS AND METHODS

Forty patients undergoing abdominal portal-venous CT at different tube voltage levels (90, 100, 110, and 120 kVp, n = 10 each) and 10 consecutive patients undergoing abdominal non-enhanced low-dose CT (100 kVp, 60 mAs) using a third-generation dual-source 192 section CT machine in the single-source mode were included. Images were reconstructed with filtered back projection (FBP) and ADMIRE (strength levels 1-5). Two blinded, independent readers subjectively determined image noise, artefacts, visibility of small structures, and image contrast, and measured attenuation in the liver, spleen, kidney, muscle, fat, and urinary bladder, and objective image noise.

RESULTS

Subjective noise was significantly lower and image contrast significantly higher for each increasing ADMIRE strength level and also for ADMIRE 1 compared to FBP (all, p < 0.001). No significant differences were found for artefact and visibility ratings among image sets (all, p > 0.05). Attenuation was similar across tube voltage-image datasets in all anatomical regions (all, p > 0.05). Objective noise was significantly lower for each increasing ADMIRE strength level, and for ADMIRE 1 compared to FBP (all, p < 0.001, maximal reduction 53%). Independent predictors of noise were tube voltage (p < 0.05) and current (p < 0.001), diameter (p < 0.05), and reconstruction algorithm (p<0.001); the amount of noise reduction was related only to the reconstruction algorithm (p < 0.001).

CONCLUSION

Abdominal CT using ADMIRE results in an improved image quality with lower image noise as compared with FBP, while the attenuation of various anatomical regions remains constant among reconstruction algorithms.

Spinal cord motion: influence of respiration and cardiac cycle

PURPOSE

To assess physiological spinal cord motion during the cardiac cycle compared with the influence of respiration based on magnetic resonance imaging (MRI) measurements.

MATERIALS AND METHODS

Anterior-posterior spinal cord motion within the spinal canal was assessed in 16 healthy volunteers (median age, 25 years) by cardiac-triggered and cardiac-gated gradient echo pulse sequence MRI. Image acquisition was performed during breath-holding, normal breathing, and forced breathing. Normal spinal cord motion values were computed using descriptive statistics. Breathing-dependent differences were assessed using the Wilcoxon signed-rank test and compared with the cardiac-based cord motion.

RESULTS

A normal value table was set up for the spinal cord motion of each vertebral cervico-thoracic-lumbar segment. Significant differences in cord motion were found between cardiac-based motion while breath-holding and the two breathing modalities (P < 0.01 each). Spinal cord motion was found to be highest during forced breathing, with a maximum in the lower cervical spinal segments (C5; mean, 2.1 mm ± 1.17). Image acquisition during breath-holding revealed the lowest motion.

CONCLUSION

MRI permits the demonstration and evaluation of cardiac and respiration-dependent spinal cord motion within the spinal canal from the cervical to lumbar segments. Breathing conditions have a considerably greater impact than cardiac activity on spinal cord motion.

KEY POINTS

• Cardiac-triggered and ECG-gated MRI allows for demonstration of the smallest spinal cord motions.• Respiratory influences seem to have the highest impact on spine motion.• In contrast, the influence of the cardiac cycle seems to be small.• The smallest spinal cord motions were measured during breath-hold.

Metallic artefact reduction with monoenergetic dual-energy CT: systematic ex vivo evaluation of posterior spinal fusion implants from various vendors and different spine levels

OBJECTIVES

To evaluate optimal monoenergetic dual-energy computed tomography (DECT) settings for artefact reduction of posterior spinal fusion implants of various vendors and spine levels.

METHODS

Posterior spinal fusion implants of five vendors for cervical, thoracic and lumbar spine were examined ex vivo with single-energy (SE) CT (120 kVp) and DECT (140/100 kVp). Extrapolated monoenergetic DECT images at 64, 69, 88, 105 keV and individually adjusted monoenergy for optimised image quality (OPTkeV) were generated. Two independent radiologists assessed quantitative and qualitative image parameters for each device and spine level.

RESULTS

Inter-reader agreements of quantitative and qualitative parameters were high (ICC = 0.81-1.00, κ = 0.54-0.77). HU values of spinal fusion implants were significantly different among vendors (P < 0.001), spine levels (P < 0.01) and among SECT, monoenergetic DECT of 64, 69, 88, 105 keV and OPTkeV (P < 0.01). Image quality was significantly (P < 0.001) different between datasets and improved with higher monoenergies of DECT compared with SECT (V = 0.58, P < 0.001). Artefacts decreased significantly (V = 0.51, P < 0.001) at higher monoenergies. OPTkeV values ranged from 123-141 keV. OPTkeV according to vendor and spine level are presented herein.

CONCLUSIONS

Monoenergetic DECT provides significantly better image quality and less metallic artefacts from implants than SECT. Use of individual keV values for vendor and spine level is recommended.

KEY POINTS

• Artefacts pose problems for CT following posterior spinal fusion implants. • CT images are interpreted better with monoenergetic extrapolation using dual-energy (DE) CT. • DECT extrapolation improves image quality and reduces metallic artefacts over SECT. • There were considerable differences in monoenergy values among vendors and spine levels. • Use of individualised monoenergy values is indicated for different metallic hardware devices.

[Cardiac low-dose computed tomography]

Cardiac CT has evolved to a robust and accurate imaging modality in the cardiac diagnostic armamentarium. However, technical developments had been accompanied with an overall increase in radiation exposure. In the last years, several technical developments and algorithms aimed at the reduction of radiation exposure in cardiac CT. The most relevant dose reduction strategies will be highlighted in this article including appropriate indications for cardiac CT, different ECG synchronization techniques, reduction of tube voltage, and high-pitch CT studies.

CT- and MRI-based volumetry of resected liver specimen: comparison to intraoperative volume and weight measurements and calculation of conversion factors

OBJECTIVE

To compare virtual volume to intraoperative volume and weight measurements of resected liver specimen and calculate appropriate conversion factors to reach better correlation.

METHODS

Preoperative (CT-group, n=30; MRI-group, n=30) and postoperative MRI (n=60) imaging was performed in 60 patients undergoing partial liver resection. Intraoperative volume and weight of the resected liver specimen was measured. Virtual volume measurements were performed by two readers (R1,R2) using dedicated software. Conversion factors were calculated.

RESULTS

Mean intraoperative resection weight/volume: CT: 855 g/852 mL; MRI: 872 g/860 mL. Virtual resection volume: CT: 960 mL(R1), 982 mL(R2); MRI: 1112 mL(R1), 1115 mL(R2). Strong positive correlation for both readers between intraoperative and virtual measurements, mean of both readers: CT: R=0.88(volume), R=0.89(weight); MRI: R=0.95(volume), R=0.92(weight). Conversion factors: 0.85(CT), 0.78(MRI).

CONCLUSION

CT- or MRI-based volumetry of resected liver specimen is accurate and recommended for preoperative planning. A conversion of the result is necessary to improve intraoperative and virtual measurement correlation. We found 0.85 for CT- and 0.78 for MRI-based volumetry the most appropriate conversion factors.

Low-dose CT coronary angiography in the step-and-shoot mode: diagnostic performance

OBJECTIVE

To investigate the performance of low-dose, dual-source computed tomography (DSCT) coronary angiography in the step-and-shoot (SAS) mode for the diagnosis of significant coronary artery stenoses in comparison with conventional coronary angiography (CCA).

DESIGN, SETTING AND PATIENTS

Prospective, single-centre study conducted in a referral centre enrolling 120 patients (71 men, mean (SD) age 68 (9) years, mean (SD) body mass index 26.2 (3.2) kg/m2). All study participants underwent DSCT in the SAS mode and CCA within 14 days. Twenty-seven patients were given intravenous beta blockers for heart rate reduction before CT. Patients were excluded if a target heart rate <or=70 bpm could not be achieved by beta blockers or when the patients were in non-sinus rhythm. Two blinded readers independently evaluated coronary artery segments for assessability and for the presence of significant (>50%) stenoses. Sensitivity, specificity, negative (NPV) and positive predictive values (PPV) were determined, with CCA being the standard of reference. Radiation dose values were calculated.

RESULTS

DSCT coronary angiography in the SAS mode was successfully performed in all 120 patients. Mean (SD) heart rate during scanning was 59 (6) bpm (range 44-69). 1773/1803 coronary segments (98%) were depicted with a diagnostic image quality in 109/120 patients (91%). The overall patient-based sensitivity, specificity, PPV and NPV for the diagnosis of significant stenoses were 100%, 93%, 94% and 100%, respectively. The mean (SD) effective dose of the CT protocol was 2.5 (0.8) mSv (range 1.2-4.4).

CONCLUSIONS

DSCT coronary angiography in the SAS mode allows, in selected patients with a regular heart rate, the accurate diagnosis of significant coronary stenoses at a low radiation dose.

A New Concept for Covered stent Protected Carotid Angioplasty: An ex vivo Study

OBJECTIVE

To determine the efficacy of a covered stent prototype designed for protected carotid angioplasty to reduce cerebral embolization.

MATERIAL AND METHOD

The covered stent tested is made of nitinol, coated with a polyurethane membrane (MembraX trade mark; porous size 80 micro m). In a bench-top model (flow-rate 650 ml/min, pulsatile flow [dicrote] 123 Pulses/min, pressure 100/60 mm Hg [mean pressure 80 mmHg]) with inserted human carotid (n = 6) stent implantation was performed (8/32 mm). Passed particles (mg) were determined in the effluent of a 100 micro m filter prior to intervention, after stent deployment and after final dilation (5 mm).

RESULTS

When stenting carotid arteries obtained from human cadavers, the highest rate of particle embolization was measured while crossing the lesion with the delivery device (6,8 mg; for all p < 0,05), embolization after additional balloon angioplasty and particle rates measured in the effluent filter prior covered stent placement were significantly lower (3,8 mg; p < 0,05). Branches of the external carotid artery remained patent in all cases.

CONCLUSIONS

The introduced concept of covered stent protected carotid angioplasty with the MembraX trade mark prototype has proven promising results for low cerebral embolization rates ex vivo. Further evaluations using an animal model and a miniaturization of the delivery device are warranted prior to human use.