14.1 MRI of the CNS
- Patients referred for MRI of the central nervous system with contrast were enrolled in two clinical trials that evaluated the visualization characteristics of lesions. In ...
14.1 MRI of the CNS
Patients referred for MRI of the central nervous system with contrast were enrolled in two clinical trials that evaluated the visualization characteristics of lesions. In both studies, patients underwent a baseline, pre-contrast MRI prior to administration of Gadavist at a dose of 0.1 mmol/kg, followed by a post-contrast MRI. In Study A, patients also underwent an MRI before and after the administration of gadoteridol. The studies were designed to demonstrate superiority of Gadavist MRI to non-contrast MRI for lesion visualization. For both studies, pre-contrast and pre-plus-post contrast images (paired images) were independently evaluated by three readers for contrast enhancement and border delineation using a scale of 1 to 4, and for internal morphology using a scale of 1 to 3 (Table 5). Lesion counting was also performed to demonstrate non-inferiority of paired Gadavist image sets to pre-contrast MRI. Readers were blinded to clinical information.
Efficacy was determined in 657 subjects. The average age was 49 years (range 18 to 85 years) and 42% were male. The ethnic representations were 39% Caucasian, 4% Black, 16% Hispanic, 38% Asian, and 3% of other ethnic groups.
Table 6 shows a comparison of visualization results between paired images and pre-contrast images. Gadavist provided a statistically significant improvement for each of the three lesion visualization parameters when averaged across three independent readers for each study.
Performances of Gadavist and gadoteridol for visualization parameters were similar. Regarding the number of lesions detected, Study B met the prespecified noninferiority margin of -0.35 for paired read versus pre-contrast read while in Study A, Gadavist and gadoteridol did not.
For the visualization endpoints contrast enhancement, border delineation, and internal morphology, the percentage of patients scoring higher for paired images compared to pre-contrast images ranged from 93% to 99% for Study A, and 95% to 97% for Study B. For both studies, the mean number of lesions detected on paired images exceeded that of the pre-contrast images; 37% for Study A and 24% for Study B. There were 29% and 11% of subjects in which the pre-contrast images detected more lesions for Study A and Study B, respectively.
The percentage of patients whose average reader mean score changed by ≤ 0, up to 1, up to 2, and ≥ 2 scoring categories presented in Table 5 is shown in Table 7. The categorical improvement of (≤ 0) represents higher (< 0) or identical (= 0) scores for the pre-contrast read, the categories with scores > 0 represent the magnitude of improvement seen for the paired read.
For both studies, the improvement of visualization endpoints in paired Gadavist images compared to pre-contrast images resulted in improved assessment of normal and abnormal CNS anatomy.
Pediatric Patients
Two studies in 44 pediatric patients age younger than 2 years and 135 pediatric patients age 2 to less than 18 years with CNS and non-CNS lesions supported extrapolation of adult CNS efficacy findings. For example, comparing pre vs paired pre- and post-contrast images, investigators selected the best of four descriptors under the heading, “Visualization of lesion-internal morphology (lesion characterization) or homogeneity of vessel enhancement” for 27/44 (62% = pre) vs 43/44 (98% = paired) MR images from patients age 0 to less than 2 years and 106/135 (78% = pre) vs 108/135 (80% = paired) MR images from patients age 2 to less than 18 years.
14.2 MRI of the Breast
Patients with recently diagnosed breast cancer were enrolled in two identical clinical trials to evaluate the ability of Gadavist to assess the presence and extent of malignant breast disease prior to surgery. Patients underwent non-contrast breast MRI (BMR) prior to Gadavist (0.1 mmol/kg) breast MRI. BMR images and Gadavist BMR (combined contrast plus non-contrast) images were independently evaluated in each study by three readers blinded to clinical information. In separate reading sessions the BMR images and Gadavist BMR images were also interpreted together with X-ray mammography images (XRM).
The studies evaluated 787 patients: Study 1 enrolled 390 women with an average age of 56 years, 74% were white, 25% Asian, 0.5% black, and 0.5% other; Study 2 enrolled 396 women and 1 man with an average age of 57 years, 71% were white, 24% Asian, 3% black, and 2% other.
The readers assessed 5 regions per breast for the presence of malignancy using each reading modality. The readings were compared to an independent standard of truth (SoT) consisting of histopathology for all regions where excisions were made and tissue evaluated. XRM plus ultrasound was used for all other regions.
The assessment of malignant disease was performed using a region based within-subject sensitivity. Sensitivity for each reading modality was defined as the mean of the percentage of malignant breast regions correctly interpreted for each subject. The within-subject sensitivity of Gadavist BMR was superior to that of BMR. The lower bound of the 95% Confidence Interval (CI) for the difference in within-subject sensitivity ranged from 19% to 42% for Study 1 and from 12% to 27% for Study 2. The within-subject sensitivity for Gadavist BMR and BMR as well as for Gadavist BMR plus XRM and BMR plus XRM is presented in Table 8.
Specificity was defined as the percentage of non-malignant breasts correctly identified as non-malignant. The lower limit of the 95% confidence interval for specificity of Gadavist BMR was greater than 80% for 5 of 6 readers. (Table 9)
Three additional readers in each study read XRM alone. For these readers over both studies, sensitivity ranged from 68% to 73% and specificity in non-malignant breasts ranged from 86% to 94%.
In breasts with malignancy, a false positive detection rate was calculated as the percentage of subjects for which the readers assessed a region as malignant which could not be verified by SoT. The false positive detection rates for Gadavist BMR ranged from 39% to 53% (95% CI Upper Bounds ranged from 44% to 58%).
14.3 MRA
Patients with known or suspected disease of the supra-aortic arteries (for evaluation up to but excluding the basilar artery) were enrolled in Study C, and patients with known or suspected disease of the renal arteries were enrolled in Study D. In both studies, non-contrast, 2D time-of-flight (ToF) magnetic resonance angiography (MRA) was performed prior to Gadavist MRA using a single intravenous injection of 0.1 mmol/kg. The injection rate of 1.5 mL/second was selected to extend the injection duration to at least half of the imaging duration. Imaging was performed with parallel-channel, 1.5T MRI devices and an automatic bolus tracking technique to trigger the image acquisition following Gadavist administration using elliptically encoded, T1-weighted, 3D gradient-echo image acquisition and single breath hold. Three central readers blinded to clinical information interpreted the ToF and Gadavist MRA images. Three additional central readers interpreted separately acquired computed tomographic angiography (CTA) images, which were used as the standard of reference (SoR) in each study.
The studies included 749 subjects: 457 were evaluated in Study C, with an average age of 68 (range 25–93); 64% were male; 80% white, 28% black, and 16% Asian. An additional 292 subjects were evaluated in Study D, with an average age of 55 (range 18–88); 54% were male; 68% white, 7% black, and 22% Asian.
Efficacy was evaluated based on anatomical visualization and performance for distinguishing between normal and abnormal anatomy. The visualization metric depended on whether readers selected, “Yes, it can be visualized along its entire length...” when responding to the question, “Is this segment assessable?” Twenty-one segments in Study C and six segments in Study D were presented per subject to each reader. The performance metrics, sensitivity and specificity, depended on digital caliper-based quantitation of arterial narrowing in visualized, non-occluded, abnormal-appearing segments. Significant stenosis was defined as at least 70% in Study C and 50% in Study D. Performance of Gadavist MRA compared to ToF MRA was calculated using an imputation method for non-visualized segments by assigning them as a 50% match with SoR and a 50% mismatch. Performance of Gadavist MRA compared to a pre-specified threshold of 50% was calculated after excluding non-visualized segments. Measurement variability and visualization of accessory renal arteries was also evaluated.
Results were analyzed for each of the three central readers.
Table 10: Visualization, Sensitivity, Specificity
GAD MRA = Post-contrast Gadavist Magnetic Resonance Angiography, ToF = Non-contrast 2D-Time of Flight.
For all three supra-aortic artery readers in Study C, the lower bound of confidence for the sensitivity of Gadavist MRA did not exceed 54%. For all three renal artery readers in Study D, the lower bound of confidence for the sensitivity of Gadavist MRA did not exceed 46%.
Measurement Variability
For both MRA and CTA, readers varied in the quantity of narrowing they assigned to the same arterial segments. Table 11 shows the percentage of patients in whom the measurement range was 30% or greater for the left or right internal carotid and proximal renal artery segments. There were approximately four measurements per patient segment, one from the site and three central readers. Measurement variability was high for both CTA and MRA, but numerically lower for Gadavist compared to non-contrast ToF MRA.
Table 11: Percent of Patients with Range ≥ 30%, ≥ 50%, ≥ 70% for Measurement of Stenoses and Normal Vessel Diameters
Visualization of Accessory Renal Arteries for Surgical Planning and Renal Donor Evaluation (Study D only)
Of 1752 main arteries visualized by the central CTA readers, 266 (15%) were also associated with positive visualization of at least one accessory (duplicate) artery. With the central MRA readers, the comparable rates were 232 of 1752 (13%) for Gadavist MRA compared to 53 of 1752 (3%) for ToF MRA.
14.4 Cardiac MRI
Two studies similar in design, Study E and Study F, evaluated the sensitivity and specificity of Gadavist cardiac MRI (CMRI) for detection of coronary artery disease (CAD) in adult patients with known or suspected CAD. Patients were excluded from study if they had a history of coronary artery bypass grafting, or if it was known in advance that they were unable to hold their breath, or had atrial fibrillation or other arrhythmia likely to prevent electrocardiogram-gated CMRI. The studies were multi-center, open-label, and evaluated 764 subjects for efficacy: 376 in Study E, with an average age of 59 (range 20–84); 69% male; 74% white, 1% black, and 25% Asian; and 388 subjects in Study F, with an average age of 59 (range 23–82); 61% male; 67% white, 17% black, and 12% Asian.
All subjects underwent dynamic first-pass Gadavist imaging during vasodilator stress, followed ~10 minutes later by dynamic first-pass Gadavist imaging at rest, followed ~5 minutes later with imaging during a period of gradual Gadavist washout from the myocardium (late gadolinium enhancement, LGE). Imaging was performed on 1.5 T or 3.0 T MRI devices equipped with multichannel surface coils to support accelerated acquisitions with parallel imaging, T1-weighted, 2D gradient-echo, dynamic acquisition of perfusion with at least 3 slices per heartbeat. Gadavist was administered intravenously at a rate of ~4 mL/second as two separate bolus injections (0.05 mmol/kg each), the first at peak pharmacologic stress (~3 minutes after start of ongoing adenosine infusion, or immediately after completion of regadenoson administration, at approved doses). No additional Gadavist was administered for LGE imaging.
Images were read by three independent readers blinded to clinical information. Reader detection of CAD depended on visually detecting defective perfusion or scar on Gadavist CMRI (stress, rest, LGE) imaging. Quantitative coronary angiography (QCA) was used to measure intraluminal narrowing and served as the standard of reference (SoR). Computed tomographic angiography (CTA) was used as the SoR if disease could be unequivocally excluded, and no coronary angiography (CA) was available. The left ventricular myocardium was divided into six regions. Readers provided per-region (CMRI, CTA) and per-artery (QCA) interpretations for each subject. Subject-level endpoints reflected each subject’s most abnormal localized finding.
The sensitivity results for Gadavist CMRI to detect CAD defined as either maximum stenosis ≥ 50% or ≥ 70% by QCA are presented in Table 12. For each reader, sensitivity of Gadavist CMRI larger than 60% can be concluded if the lower 95% confidence limit of the sensitivity estimate exceeds the pre-specified threshold of 60%.
Table 12: Sensitivity (%) of Gadavist-CMRI for Detection of CAD in Patients with Maximum Stenosis* of ≥ 50% and ≥ 70%
* Stenosis determined by Quantitative Coronary Angiography (QCA)
** CMRI images were assessed by six independent blinded readers, three in each study.
*** The bolded value represents the lower limit of the 95% confidence interval, which is compared to a pre-specified threshold of 60% for evaluation of sensitivity.
The specificity results for Gadavist CMRI to detect CAD defined as either maximum stenosis ≥50% or ≥70% by QCA are presented in Table 13. For each reader, specificity of Gadavist CMRI larger than 55% can be concluded if the lower 95% confidence limit of the specificity estimate exceeds the pre-specified threshold of 55%.
Table 13: Specificity (%) of Gadavist CMRI for Exclusion of CAD in Patients with Maximum Stenosis* of ≥ 50% and ≥ 70%.
* Stenosis determined by Quantitative Coronary Angiography (QCA)
** CMRI images were assessed by six independent blinded readers, three in each study.
*** The bolded value represents the lower limit of the 95% confidence interval, which is compared to a pre-specified threshold of 55% for evaluation of specificity.
In Study E, among the 33 patients with maximum stenosis by QCA between 50% and <70%, the proportion of Gadavist-CMRI positive detections of CAD ranged from 15% to 33%. In Study F, among the 45 patients with maximum stenosis by QCA between 50% and < 70%, the proportion of Gadavist-CMRI positive detections of CAD ranged from 20% to 35%. The results of Gadavist CMRI reads to detect CAD in patients with maximum stenosis between 50% and < 70% are summarized in Table 14.
Table 14: Gadavist-CMRI Detection of CAD in Patients with Maximum Stenosis* between 50% and < 70%
* Stenosis determined by Quantitative Coronary Angiography (QCA).
**CMRI images were assessed by six independent blinded readers, three in each study.
Left Mainstem Stenosis (LMS)
The studies did not include sufficient numbers of subjects to characterize the performance of Gadavist CMRI for detection of LMS, a subgroup at high risk from false negative reads. In Studies E and F, only three subjects had isolated LMS stenosis >50%. In two of the three cases, the CMRI was interpreted as normal by at least two of the three readers (false negative). Sixteen subjects had LMS stenosis >50% (including subjects with isolated LMS stenosis and subjects with LMS stenosis in addition to stenoses elsewhere). In five of these sixteen cases, the CMR was interpreted as normal by at least two of the three readers (false negative).
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