DOI: 10.1148/radiol.2433060155
(Radiology 2007;243:837-846.)
© RSNA, 2007
Contrast-enhanced MR Angiography of the Chest and Abdomen with Use of Controlled Apnea in Children1
Roya S. Saleh, MD,
Swati Patel, MD,
Margaret H. Lee, MD,
M. Ines Boechat, MD,
Osman Ratib, MD, PhD,
Carla R. Saraiva, MD, and
J. Paul Finn, MD
1 From the Departments of Radiology (R.S.S., M.H.L., M.I.B., O.R., C.R.S., J.P.F.) and Anesthesiology (S.P.), Division of Diagnostic Cardiovascular Imaging, Magnetic Resonance Research Center, University of California Los Angeles, Peter V. Uberroth Bldg, Suite 3371, 10945 Le Conte Ave, Los Angeles, CA 90095-7206. Received January 26, 2006; revision requested March 27; revision received May 5; accepted June 1; final version accepted September 5.
Address correspondence to R.S.S. (e-mail: rsaleh{at}mednet.ucla.edu).
 |
ABSTRACT
|
|---|
Purpose: To retrospectively determine if controlled apnea improves the image quality of contrast material–enhanced magnetic resonance (MR) angiography of the chest and abdomen in children.
Materials and Methods: Institutional review board approval and waiver of informed consent were obtained for this HIPAA-compliant study. The authors evaluated contrast-enhanced MR angiographic procedures performed in the chest, abdomen, or both, in 23 children (14 boys, nine girls; age range, 1 month to 8 years) who were under general anesthesia. All patients underwent mechanical ventilation with preoxygenation (100% oxygen) prior to controlled apnea during image acquisition. In control subjects, the authors assessed contrast-enhanced MR angiographic procedures performed in the chest, abdomen, or both, in 23 children (matched for age and type of study with children in the controlled apnea group; 11 boys, 12 girls; age range, 1 month to 8 years) who were under general anesthesia (n = 15) or deep sedation (n = 8) and were breathing spontaneously during image acquisition. MR angiograms of the chest, abdomen, or both, were assessed for image quality, motion artifacts, and vessel definition by two radiologists working in consensus with a subjective grading scale. Wilcoxon signed rank test was used to assess differences in measurements.
Results: Image quality was rated excellent in 97% (30 of 31) of studies with controlled apnea and in 30% (nine of 31) of control studies (P < .001). Motion artifacts were absent in 97% (30 of 31) of studies with controlled apnea and 13% (four of 31) of control studies (P < .001). Vessel sharpness was rated as being significantly better on images obtained with controlled apnea (P < .05). There were no complications caused by anesthesia or sedation in either group.
Conclusion: Controlled apnea is highly effective in children for eliminating respiratory motion artifacts with contrast-enhanced MR angiographic studies, resulting in greatly improved image quality and spatial resolution.
© RSNA, 2007
|
INTRODUCTION
|
|---|
In children, contrast material–enhanced magnetic resonance (MR) angiography is an attractive technique in the diagnostic evaluation of the vascular system. Catheter angiography is invasive and exposes children to ionizing radiation and iodinated contrast agents (1–3), while computed tomographic (CT) angiography is associated with high radiation exposure, even when fast multidetector CT scanners are used (4,5). The radiation burden of multidetector CT may be further exacerbated if multiphase CT angiography is used. Ultrasonography is a safe alternative, but it may be limited by the available acoustic window settings, especially in the thorax (6–8). The safety of MR imaging (9) makes it a particularly desirable modality for use in the pediatric population.
Contrast-enhanced MR angiography is sensitive to motion artifacts, which, if severe, may render images nondiagnostic. Since breathing is the primary source of motion artifacts in the body, breath holding is routinely used in cooperative adults (10,11). In young children, however, breath holding may be impractical or impossible. Moreover, while deep sedation can help control gross body motion artifacts, it cannot control respiratory motion artifacts. General anesthesia is advantageous in pediatric MR imaging, as it protects the airway and prevents hypoxemia (12–15) and gross body movement. However, general anesthesia does not alleviate respiratory motion artifacts when patients breathe spontaneously (16,17). Mechanical ventilation with controlled apnea during image acquisition has been described in children undergoing cardiac MR imaging and contrast-enhanced MR angiography (18); however, it is not widely used. Furthermore, there is no clear consensus on when efforts to control respiration are warranted or on the extent to which such control improves the diagnostic quality of the images.
Thus, the purpose of our study was to retrospectively determine if controlled apnea improves the image quality of contrast-enhanced MR angiography of the chest and abdomen in children.
|
MATERIALS AND METHODS
|
|---|
One author (J.P.F.) is a consultant for Siemens Medical Solutions (Malvern, Pa). Authors without a financial interest controlled data and information that could have caused a conflict of interest.
Our Health Insurance Portability and Accountability Act–compliant retrospective study was approved by the institutional review board, and the informed consent requirement was waived. In March 2004, we adopted a protocol for mechanical ventilation during general anesthesia in children undergoing contrast-enhanced MR angiography of the chest, abdomen, or both, and we used controlled apnea during image acquisition (18).
Study and Control Groups
In 23 children (14 boys, nine girls; 19 patients were older than 1 year, four were infants; mean age, 32 months; age range, 1 month to 8 years; median age, 23 months), 31 sequential contrast-enhanced MR angiographic studies with controlled apnea (17 thoracic, 14 abdominal) were performed in patients under general anesthesia by using mechanical ventilation with high inspired oxygen concentration (19,20).
In the control group, 31 sequential contrast-enhanced MR angiographic studies were performed in 23 children who were selected from a larger group and who were matched with children in the controlled apnea group for type of MR angiographic study (abdominal, thoracic, or both) and age (11 boys, 12 girls; 19 patients were older than 1 year, four were infants; mean age, 29 months; age range, 1 month to 8 years; median age, 24 months).
All studies were performed between January 2002 and March 2004. The same MR imaging machine was used in the experimental studies with controlled apnea and the control studies with spontaneous breathing.
The two groups were matched according to anatomic region of interest (abdominal or chest MR angiography) and age (matched within 6 months for children younger than 2 years and within 1 year for children older than 2 years). Six children underwent sequential MR angiography with and without controlled apnea on separate occasions. Eight children underwent both thoracic and abdominal MR angiography; these children were matched with eight control subjects who underwent both thoracic and abdominal MR angiography. Four children in the controlled apnea group each underwent four sequential studies with controlled ventilation. The results of these studies were evaluated to assess the reproducibility of this technique. The anesthesia records of all patients were reviewed (S.P.) to reaffirm the safety of this procedure, as established in prior studies (18,21–23). Clinical details and final diagnoses in both groups were retrieved from the patients' medical records (R.S.S.).
Anesthesia Procedure
After a full physical examination, clinical history taking, and laboratory work-up, specialist pediatric anesthesiologists (S.P.) performed all anesthetic procedures in the MR imaging suite. General anesthesia was induced in all patients in the controlled apnea group, except for one patient who came from the intensive care unit and was already intubated and sedated. In the control group, general anesthesia was induced in 15 patients and intravenous deep sedation was induced in eight. General anesthesia was induced by means of intravenous administration of propofol or etomidate or, in patients without preexisting intravenous access, by means of inhalational anesthesia (sevoflurane, nitrous oxide, and oxygen). Muscle relaxation was established with a nondepolarizing neuromuscular blocker (vecuronium, rocuronium, or cisatracurium). Anesthesia was maintained with propofol infusion or inhalation of a mixture of nitrous oxide (70%), oxygen (30%), and sevoflurane. Standard American Society of Anesthesiologists physiologic monitoring was performed (electrocardiography, pulse oximetry, and noninvasive measurement of blood pressure and end-tidal CO2 level) with an MR imaging–compatible monitoring system (Magnitude 3150 MRI patient monitor; InVivo Research, Orlando, Fla). An MR imaging–compatible anesthesia machine and ventilator (Narkomed MRI_2, Drager Medical, Telford, Pa) was used in all cases.
Continuous monitoring of tidal volume, minute ventilation, and airway pressure was performed. Intravenous access was established in an upper extremity antecubital vein in all patients except three children, in whom only a foot vein was accessible. In all cases, the intravenous catheter was connected to an electronic injector (Spectris Solaris; Medrad, Indianola, Pa) for precise demand delivery of the gadolinium-containing contrast agent (see below).
Of the patients in the controlled apnea group, one had undergone tracheostomy, and one came from the intensive care unit and was already intubated and sedated. Patients in the control group did not receive a muscle relaxant and were allowed to breathe spontaneously.
In the controlled apnea group, the anesthesiologist remained in the MR imaging room with the patient and communicated continuously with the MR imaging technologist and the attending radiologist. Preoxygenation with 100% oxygen and mild hyperventilation was used for at least 1 minute immediately prior to suspension of ventilation for those sequences that required apnea. The average acquisition time with a contrast-enhanced MR angiographic pulse sequence was 20 seconds, and up to two images were obtained concurrently, for a total apneic period of 40 seconds. After the breath-hold sequences were completed and ventilation was resumed, the high inspired oxygen concentration was returned to the baseline level. Heart rate and pulse oximetry were continuously monitored throughout the apneic period.
MR Angiography
Set-up.—All studies were performed with a four-channel 1.5-T MR imager (Magnetom Sonata; Siemens Medical Solutions) with use of a head coil, knee coil, or body phased-array coil, as appropriate for patient size. After successful intubation and stabilization of the patient, he or she was placed in the supine position with the appropriate coil(s) in place and advanced into the imager bore.
Imaging.—Single-shot steady-state free precession survey images (24) were acquired in sagital, coronal, and transverse planes. The acquisition time required for these images was less than 1 minute, and breath holding was not used in this phase. For contrast-enhanced MR angiography, contrast material dose and infusion rate were adjusted on the basis of patient body weight to a total dose of 0.25 mmol per kilogram of body weight. Mean contrast agent volumes were 11 and 9 mL in the apnea and control groups, respectively. Gadodiamide (Omniscan; GE Amersham Healthcare, Princeton, NJ) was injected at a rate of 0.2–0.7 mL/sec (rate depended on patient size) and followed by a 10-mL bolus of normal saline administered at the same infusion rate. The infusion rate was adjusted so that the infusion time was 15 seconds. To determine the appropriate image delay, a timing run with 1 mL of gadodiamide infused at the same rate as that used with the main contrast agent bolus was used. The sequence used for the timing run was an inversion-recovery spoiled gradient-echo sequence (repetition time msec/echo time msec/inversion time msec, 1000/1.58/300; flip angle, 10°; bandwidth, 375 Hz per pixel; matrix, 100 x 256).
For contrast-enhanced MR angiography, a short-repetition-time, short-echo-time three-dimensional spoiled gradient-echo sequence was used. Imaging was performed before, during, and immediately after injection of the contrast agent and resulted in mask images, arterial phase images, and venous phase images. During controlled apnea, arterial and venous phase images were acquired during one extended breath hold (40 seconds). A nearly identical protocol was used in all patients who underwent MR angiography with controlled apnea (repetition time msec/echo time msec, 2.9/1.0; flip angle, 20°; sampling bandwidth, 620 Hz per pixel; section thickness, 1.2 mm; slab thickness, 76 mm; matrix larger than 202 x 448; field of view [tailored to patient size] larger than 174 x 270 mm; acquisition time, 19.30 seconds). Sequence parameters for the control group were as follows: 2.8–3.8/0.9–1.3; flip angle, 25°; bandwidth, 490–600 Hz per pixel; section thickness, 1.2–1.6 mm; slab thickness, 48–96 mm; and acquisition time, 21 seconds. The 23 children in the apnea group and the 23 children in the control group successfully underwent chest and abdominal MR angiography.
Evaluation.—Qualitative evaluation was performed in consensus by two board-certified radiologists (M.I.B., M.H.L.) with 20 and 5 years of experience in body MR imaging, respectively. The reviewers were blinded to patients' information and clinical reports and to whether the images were acquired with or without controlled apnea. The reviewers had access to the three-dimensional partition MR angiograms, full-thickness maximum intensity projections (MIPs), and multiple overlapping thin MIP reconstructions. All images were reviewed on a three-dimensional workstation (Leonardo; Siemens Medical Solutions). The images were subjectively scored for overall image quality and motion artifacts (Table 1).
Vessel definition was also subjectively evaluated with a scale agreed on by the observers to reflect the clarity of the depiction and sharpness of each vessel. Definition of the following structures was assessed by using a four-point scoring scale for larger branch arteries and a three-point scoring scale for smaller branch arteries. In larger branch arteries (celiac, proximal superior mesenteric, common hepatic, right hepatic, and renal arteries), excellently defined arteries were given a score of 3; well-defined arteries, a score of 2; poorly defined arteries, a score of 1; and arteries that were not seen, a score of 0. In smaller branch arteries (left hepatic and inferior mesenteric arteries and second- and third-order branches of the superior mesenteric artery), a score of 2 was given to well-defined arteries; a score of 1, to poorly defined arteries; and a score of 0, to arteries that were not seen. Overall, 10 arterial segments in the abdomen were assessed for vessel sharpness in each patient.
For contrast-enhanced MR angiography of the thorax, up to fourth-order pulmonary vessel branches were evaluated in both the upper and the lower lobes of each lung with a four-point scale based on the same scoring system as that used with abdominal larger branch arteries (excellently defined artery, 3; well-defined artery, 2; poorly defined artery, 1; and artery not seen, 0).
Statistical Analysis
The Wilcoxon signed rank test was used for comparative analysis of the ordinal data for degree of image quality, motion artifact, and vessel definition. For all comparisons, P < .05 was considered to indicate a significant difference. SPSS software (version 13; SPSS, Chicago, Ill) was used for statistical analysis.
|
RESULTS
|
|---|
Patients
In the controlled apnea group, six children underwent both chest and abdominal MR angiography. The mean weight was 12.25 kg in children who underwent imaging with controlled apnea and 10.89 kg in children who underwent imaging without controlled apnea (range, 2.25–27.22 kg). Various medical referral questions were posed before MR angiographic studies were performed (Table 2), and a wide range of principal diagnoses were present (Table 3).
Anesthesia and Safety
None of the patients experienced arterial oxygen desaturation from baseline values or showed any evidence of cardiovascular or respiratory instability during the apneic period. There was no change in heart rate or rhythm during apnea in any patient, and no allergic reactions to the contrast agent were reported.
Image Assessment
Overall image quality (Fig 1) was rated as excellent in 97% (n = 30) and 29% (n = 9) of studies in the apnea and control groups, respectively (P < .001) (Figs 2, 3). Motion artifacts (Fig 4) were completely absent on images obtained in 97% (n = 30) of studies performed in the apnea group, whereas 87% (n = 27) of images obtained in the control group had motion artifacts that ranged from minimal to severe (P < .001) (Figs 2, 5). Vessel definition and sharpness were significantly (P < .05) better in the apnea group.
View larger version (22K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1: Graph shows image quality of contrast-enhanced MR angiographic studies in the apnea group and the control group. The results show clear superiority in the apnea group (P < .001).
|
|
View larger version (120K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2a: (a, b) Coronal abdominal MR angiogram (2.9/1.0, 20° flip angle) in a 2-year-old boy after liver transplantation. Note the definition of the transplanted hepatic artery (arrow) and native renal arteries. (a) Thin (20 mm) subvolume MIP and (b) full-thickness MIP. (c, d) Coronal abdominal MR angiograms (3.1/1.1, 25° flip angle) in a 22-month-old child breathing spontaneously. Patient was under deep sedation. Note the motion artifact and lack of vessel sharpness. (c) Thin (20 mm) subvolume MIP and (d) full-thickness MIP.
|
|
View larger version (119K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2b: (a, b) Coronal abdominal MR angiogram (2.9/1.0, 20° flip angle) in a 2-year-old boy after liver transplantation. Note the definition of the transplanted hepatic artery (arrow) and native renal arteries. (a) Thin (20 mm) subvolume MIP and (b) full-thickness MIP. (c, d) Coronal abdominal MR angiograms (3.1/1.1, 25° flip angle) in a 22-month-old child breathing spontaneously. Patient was under deep sedation. Note the motion artifact and lack of vessel sharpness. (c) Thin (20 mm) subvolume MIP and (d) full-thickness MIP.
|
|
View larger version (137K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2c: (a, b) Coronal abdominal MR angiogram (2.9/1.0, 20° flip angle) in a 2-year-old boy after liver transplantation. Note the definition of the transplanted hepatic artery (arrow) and native renal arteries. (a) Thin (20 mm) subvolume MIP and (b) full-thickness MIP. (c, d) Coronal abdominal MR angiograms (3.1/1.1, 25° flip angle) in a 22-month-old child breathing spontaneously. Patient was under deep sedation. Note the motion artifact and lack of vessel sharpness. (c) Thin (20 mm) subvolume MIP and (d) full-thickness MIP.
|
|
View larger version (123K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2d: (a, b) Coronal abdominal MR angiogram (2.9/1.0, 20° flip angle) in a 2-year-old boy after liver transplantation. Note the definition of the transplanted hepatic artery (arrow) and native renal arteries. (a) Thin (20 mm) subvolume MIP and (b) full-thickness MIP. (c, d) Coronal abdominal MR angiograms (3.1/1.1, 25° flip angle) in a 22-month-old child breathing spontaneously. Patient was under deep sedation. Note the motion artifact and lack of vessel sharpness. (c) Thin (20 mm) subvolume MIP and (d) full-thickness MIP.
|
|
View larger version (115K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3a: (a) Coronal chest MR angiogram (2.9/1.0, 20° flip angle) obtained with controlled apnea in a 20-month-old child. Partial anomalous pulmonary venous return is noted, with a left vertical vein (arrow) draining into the left brachiocephalic vein. Right-sided heart and pulmonary arterial enlargement due to anomalous pulmonary venous return and atrial septal defect are also seen. Thin-volume MIP (20 mm). (b) Coronal chest MR angiogram (2.9/1.1, 25° flip angle) obtained with spontaneous breathing in a 20-month-old child. Patient was under general anesthesia. Thin-volume MIP (20 mm). Image quality is moderate, but vessel sharpness is inferior to that in a.
|
|
View larger version (100K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3b: (a) Coronal chest MR angiogram (2.9/1.0, 20° flip angle) obtained with controlled apnea in a 20-month-old child. Partial anomalous pulmonary venous return is noted, with a left vertical vein (arrow) draining into the left brachiocephalic vein. Right-sided heart and pulmonary arterial enlargement due to anomalous pulmonary venous return and atrial septal defect are also seen. Thin-volume MIP (20 mm). (b) Coronal chest MR angiogram (2.9/1.1, 25° flip angle) obtained with spontaneous breathing in a 20-month-old child. Patient was under general anesthesia. Thin-volume MIP (20 mm). Image quality is moderate, but vessel sharpness is inferior to that in a.
|
|
View larger version (22K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4: Graph shows degree of motion artifact on MR angiograms in the apnea group and the control group. Data are numbers of examinations. In the control group, 27 of 31 studies resulted in some degree of motion artifact; however, in the apnea group, 30 (97%) of 31 studies did not result in motion artifacts (P < .001).
|
|
View larger version (122K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5a: (a, b) Coronal abdominal MR angiograms (2.9/1.0, 20° flip angle) in a 21-month-old boy with end-stage renal disease who was a candidate for renal transplantation. Images were acquired during apnea. Note the sharpness and visibility of vessels. (a) Full-volume MIP reconstruction of arterial phase and (b) thin (20 mm) MIP reconstruction of venous phase. (c, d) Coronal abdominal MR angiograms (3.1/1.1, 25° flip angle) in a 27-month-old boy obtained after liver transplantation and portal vein reconstruction. Child was intubated but breathing spontaneously during image acquisition. Note the degradation of image quality and vessel sharpness, particularly in smaller vessel branches (ie, left and right hepatic artery and smaller branches of superior mesenteric artery). (c) Full-volume MIP reconstruction of arterial phase and (d) thin (20 mm) MIP reconstruction of venous phase.
|
|
View larger version (136K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5b: (a, b) Coronal abdominal MR angiograms (2.9/1.0, 20° flip angle) in a 21-month-old boy with end-stage renal disease who was a candidate for renal transplantation. Images were acquired during apnea. Note the sharpness and visibility of vessels. (a) Full-volume MIP reconstruction of arterial phase and (b) thin (20 mm) MIP reconstruction of venous phase. (c, d) Coronal abdominal MR angiograms (3.1/1.1, 25° flip angle) in a 27-month-old boy obtained after liver transplantation and portal vein reconstruction. Child was intubated but breathing spontaneously during image acquisition. Note the degradation of image quality and vessel sharpness, particularly in smaller vessel branches (ie, left and right hepatic artery and smaller branches of superior mesenteric artery). (c) Full-volume MIP reconstruction of arterial phase and (d) thin (20 mm) MIP reconstruction of venous phase.
|
|
View larger version (133K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5c: (a, b) Coronal abdominal MR angiograms (2.9/1.0, 20° flip angle) in a 21-month-old boy with end-stage renal disease who was a candidate for renal transplantation. Images were acquired during apnea. Note the sharpness and visibility of vessels. (a) Full-volume MIP reconstruction of arterial phase and (b) thin (20 mm) MIP reconstruction of venous phase. (c, d) Coronal abdominal MR angiograms (3.1/1.1, 25° flip angle) in a 27-month-old boy obtained after liver transplantation and portal vein reconstruction. Child was intubated but breathing spontaneously during image acquisition. Note the degradation of image quality and vessel sharpness, particularly in smaller vessel branches (ie, left and right hepatic artery and smaller branches of superior mesenteric artery). (c) Full-volume MIP reconstruction of arterial phase and (d) thin (20 mm) MIP reconstruction of venous phase.
|
|
View larger version (135K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 5d: (a, b) Coronal abdominal MR angiograms (2.9/1.0, 20° flip angle) in a 21-month-old boy with end-stage renal disease who was a candidate for renal transplantation. Images were acquired during apnea. Note the sharpness and visibility of vessels. (a) Full-volume MIP reconstruction of arterial phase and (b) thin (20 mm) MIP reconstruction of venous phase. (c, d) Coronal abdominal MR angiograms (3.1/1.1, 25° flip angle) in a 27-month-old boy obtained after liver transplantation and portal vein reconstruction. Child was intubated but breathing spontaneously during image acquisition. Note the degradation of image quality and vessel sharpness, particularly in smaller vessel branches (ie, left and right hepatic artery and smaller branches of superior mesenteric artery). (c) Full-volume MIP reconstruction of arterial phase and (d) thin (20 mm) MIP reconstruction of venous phase.
|
|
In the abdomen, 140 branch arteries were assessed in the apnea group. All 140 arteries were visible (grades 1–3); 97% (n = 136) were graded as excellent or well defined, and 3% (n = 4) were graded as poorly defined. In the control group, 140 arterial branches were assessed. Of these, 17% (n = 24) were undefined or not visible, 21% (n = 30) were poorly defined, and 61% (n = 86) were excellent or well defined (grades 3 and 2, respectively) (Table 4).
View this table:
[in this window]
[in a new window]
|
Table 4. Distribution of Abdominal Arterial Segments on the Basis of their Rank in 14 Abdominal MR Angiographic Studies in Each Group
|
|
In the thorax, 84% (n = 229) of 272 pulmonary vessels in the apnea group were excellent; 9% (n = 25), well defined; 4% (n = 10), poorly defined; and 3% (n = 8), not visible. In the control group, 19% (n = 53) of 272 pulmonary vessels were excellent; 34% (n = 92), well defined; 19% (n = 52), poorly defined; and 28% (n = 75), not visible (Table 5).
View this table:
[in this window]
[in a new window]
|
Table 5. Distribution of Pulmonary Arterial Segments on the Basis of their Rank in 17 Chest MR Angiographic Studies in Each Group
|
|
In the control group, the definition and visibility of vessels decreased rapidly with branch order; however, in the apnea group, visibility was maintained through the smallest branches analyzed (Figs 5, 6).
View larger version (118K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 6a: Coronal chest MR angiograms in a 21-month-old girl with tetralogy of Fallot. General anesthesia was used in both studies, which were performed (a) with (2.9/1.0, 20° flip angle) and (b) without (3.1/1.0, 25° flip angle) controlled apnea. Note the large tortuous aortopulmonary collateral vessel (arrows) originating from the left innominate artery, which was visible with both techniques; however, only with controlled apnea can one follow the course of the collateral artery, left pulmonary artery, and small right pulmonary artery.
|
|
View larger version (118K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 6b: Coronal chest MR angiograms in a 21-month-old girl with tetralogy of Fallot. General anesthesia was used in both studies, which were performed (a) with (2.9/1.0, 20° flip angle) and (b) without (3.1/1.0, 25° flip angle) controlled apnea. Note the large tortuous aortopulmonary collateral vessel (arrows) originating from the left innominate artery, which was visible with both techniques; however, only with controlled apnea can one follow the course of the collateral artery, left pulmonary artery, and small right pulmonary artery.
|
|
In four children who underwent follow-up MR angiography with apnea, nine image sets were scored as excellent for image quality and no motion artifact (Fig 7).
View larger version (106K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7a: Follow-up coronal abdominal MR angiograms (2.9/1.0, 20° flip angle) obtained with controlled apnea in the same 2-year-old boy (thin [20 mm] subvolume MIP) as in Fig 2a. Image quality was excellent for all angiograms and thus suggested that the technique was reproducible. In a and b, a foot vein was used for injection of contrast material. In c, contrast material was injected through an arm vein.
|
|
View larger version (113K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7b: Follow-up coronal abdominal MR angiograms (2.9/1.0, 20° flip angle) obtained with controlled apnea in the same 2-year-old boy (thin [20 mm] subvolume MIP) as in Fig 2a. Image quality was excellent for all angiograms and thus suggested that the technique was reproducible. In a and b, a foot vein was used for injection of contrast material. In c, contrast material was injected through an arm vein.
|
|
View larger version (107K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7c: Follow-up coronal abdominal MR angiograms (2.9/1.0, 20° flip angle) obtained with controlled apnea in the same 2-year-old boy (thin [20 mm] subvolume MIP) as in Fig 2a. Image quality was excellent for all angiograms and thus suggested that the technique was reproducible. In a and b, a foot vein was used for injection of contrast material. In c, contrast material was injected through an arm vein.
|
|
|
DISCUSSION
|
|---|
The results of our study indicate that the effectiveness of contrast-enhanced MR angiography of the chest and abdomen in children is greatly improved with controlled apnea. To our knowledge, this study represents the first attempt to quantify the improved image quality that results from using controlled ventilation in the pediatric population. This is an important step in defining what results might be anticipated in appropriately selected cases. Whereas MR angiography without breath holding may be sufficient for defining the status of the aorta or large arterial branches, assessment of fine vascular detail or smaller vessels requires that respiratory motion artifacts be eliminated.
Our study addresses the extent to which motion artifacts due to breathing can limit the quality of contrast-enhanced MR angiographic images in children and the extent to which this limitation can be safely eliminated with use of controlled apnea. Without apnea, small blood vessels were obscured or rendered invisible; however, with suspended ventilation, vascular detail was greatly enhanced. Furthermore, the duration of apnea in patients who undergo ventilation with high inspired oxygen concentration can usually be extended safely to 4 minutes, if required. In our study, apnea did not exceed 40 seconds. This was adequate for our purposes; however, in principle, it is entirely possible to extend the apneic period safely (19,20). Importantly, specialized pediatric anesthesiologists were available to perform these procedures, and their presence should be regarded as crucial.
Muthupillai et al (25) and Chung (26) reported use of time-resolved MR angiography as an approach to fast imaging in children breathing spontaneously. In their studies, total imaging time was between 30 and 45 seconds and resulted in an average of seven time phases (4–7 seconds for each time phase). With a respiratory rate of 20–30 breaths per minute, a time phase of 4–7 seconds corresponded to two or three breathing cycles, which were more than enough to cause image artifacts. Moreover, faster imaging invoked a penalty in spatial resolution.
The proliferation of multidetector CT scanners has pushed the boundaries of speed and spatial resolution for evaluation of the vascular system in adults (27–29). However, there is a radiation burden associated with multidetector CT, and if multiple phases of enhancement are required, the radiation dose increases proportionately. On the other hand, with MR imaging, multiple phases of contrast enhancement can be acquired with no radiation burden. In our study, at least two phases of enhancement were acheived routinely. These allowed clear definition of arterial and venous phases of vascular enhancement.
The safety of anesthesia and endotracheal intubation for MR imaging in children has been addressed in previous studies (18,21,22). In fact, controlled ventilation offers some advantages over intravenous sedation in small children and infants. While general anesthesia is crucial to prevent gross body motion, there is a risk of airway obstruction in anesthetized or heavily sedated children within the magnet bore. Children with cyanotic congenital heart disease, which was a common disease in our study group, may experience rapid arterial desaturation if respiratory depression ensues. Endotracheal intubation and mechanical ventilation give the anesthesiologist full control of a patient's airway and his or her oxygenation and ventilation.
Our study had limitations. When comparing differences between contrast-enhanced MR angiography performed with breath holding and contrast-enhanced MR angiography performed without breath holding, one would ideally examine the same subjects with both techniques and with identical parameters. However, ethical considerations argue against unnecessary prolongation of procedures in children and administration of larger-than-necessary doses of contrast material. Furthermore, because it is intuitive that breath holding is advantageous, randomization of the order of techniques may not be in the patients' best interests. Nonetheless, six patients in the apnea group had undergone earlier studies without breath holding; these patients served as their own controls. Similarly, four patients underwent more than one breath-hold study on different occasions; these studies yielded limited data on reproducibility. Although the numbers were small, the close concordance of results argues in favor of reproducibility or at least provides no evidence of poor reproducibility.
In conclusion, controlled apnea can be used effectively in children to eliminate respiratory motion artifacts on contrast-enhanced MR angiographic images, resulting in greatly improved diagnostic quality with virtually no risk of failure. Our findings suggest that reliable definition of fine vascular detail can be achieved only if respiration is suspended during imaging. Furthermore, by using preventilation with 100% oxygen, prolonged apnea can be used safely in the majority of patients, enabling use of imaging parameters that would otherwise not be possible.
|
ADVANCE IN KNOWLEDGE
|
|---|
- Controlled apnea is highly effective in children for elimination of respiratory motion artifacts on contrast-enhanced MR angiograms, resulting in greatly improved image quality.
|
FOOTNOTES
|
|---|
Abbreviations: MIP = maximum intensity projection
See Materials and Methods for pertinent disclosures.
Author contributions: Guarantor of integrity of entire study, R.S.S.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, R.S.S., J.P.F.; clinical studies, all authors; statistical analysis, R.S.S.; and manuscript editing, R.S.S., J.P.F.
|
References
|
|---|
- Rhodes JF, Asnes JD, Blaufox AD, Sommer RJ. Impact of low body weight on frequency of pediatric cardiac catheterization complications. Am J Cardiol 2000;86:1275–1278, A9.[CrossRef][Medline]
- Vitiello R, McCrindle BW, Nykanen D, Freedom RM, Benson LN. Complications associated with pediatric cardiac catheterization. J Am Coll Cardiol 1998;32:1433–1440.[Abstract/Free Full Text]
- Shim D, Lloyd TR, Crowley DC, Beekman RH 3rd. Neonatal cardiac catheterization: a 10-year transition from diagnosis to therapy. Pediatr Cardiol 1999;20:131–133.[CrossRef][Medline]
- Brenner D, Elliston C, Hall E, Berdon W. Estimated risks of radiation-induced fatal cancer from pediatric CT. AJR Am J Roentgenol 2001;176:289–296.[Abstract/Free Full Text]
- Paterson A, Frush DP, Donnelly LF. Helical CT of the body: are settings adjusted for pediatric patients? AJR Am J Roentgenol 2001;176:297–301.[Abstract/Free Full Text]
- Masui T, Seelos KC, Kersting-Sommerhoff BA, Higgins CB. Abnormalities of the pulmonary veins: evaluation with MR imaging and comparison with cardiac angiography and echocardiography. Radiology 1991;181:645–649.[Abstract/Free Full Text]
- Reddy SC, Chopra PS, Rao PS. Mixed-type total anomalous pulmonary venous connection: echocardiographic limitations and angiographic advantages. Am Heart J 1995;129:1034–1038.[CrossRef][Medline]
- Valsangiacomo ER, Levasseur S, McCrindle BW, MacDonald C, Smallhorn JF, Yoo SJ. Contrast-enhanced MR angiography of pulmonary venous abnormalities in children. Pediatr Radiol 2003;33:92–98.[Medline]
- Wolff S, James TL, Young GB, Margulis AR, Bodycote J, Afzal V. Magnetic resonance imaging: absence of in vitro cytogenetic damage. Radiology 1985;155:163–165.[Abstract/Free Full Text]
- Maki JH, Chenevert TL, Prince MR. The effects of incomplete breath-holding on 3D MR image quality. J Magn Reson Imaging 1997;7:1132–1139.[Medline]
- Prince MR, Narasimham DL, Stanley JC, et al. Breath-hold gadolinium-enhanced MR angiography of the abdominal aorta and its major branches. Radiology 1995;197:785–792.[Abstract/Free Full Text]
- Malviya S, Voepel-Lewis T, Eldevik OP, Rockwell DT, Wong JH, Tait AR. Sedation and general anaesthesia in children undergoing MRI and CT: adverse events and outcomes. Br J Anaesth 2000;84:743–748.[Abstract/Free Full Text]
- Malviya S, Voepel-Lewis T, Prochaska G, Tait AR. Prolonged recovery and delayed side effects of sedation for diagnostic imaging studies in children. Pediatrics 2000;105:E42.
- Malviya S, Voepel-Lewis T, Tait AR, Merkel S. Sedation/analgesia for diagnostic and therapeutic procedures in children. J Perianesth Nurs 2000;15:415–422.[CrossRef][Medline]
- Lamireau T, Dubreuil M, Daconceicao M. Oxygen saturation during esophagogastroduodenoscopy in children: general anesthesia versus intravenous sedation. J Pediatr Gastroenterol Nutr 1998;27:172–175.[CrossRef][Medline]
- American Academy of Pediatrics Committee on Drugs: guidelines for monitoring and management of pediatric patients during and after sedation for diagnostic and therapeutic procedures. Pediatrics 1992;89(6 pt 1):1110–1115.[Abstract/Free Full Text]
- American Academy of Pediatrics Committee on Drugs: guidelines for monitoring and management of pediatric patients during and after sedation for diagnostic and therapeutic procedures—addendum. Pediatrics 2002;110:836–838.[Abstract/Free Full Text]
- Tsai-Goodman B, Geva T, Odegard KC, Sena LM, Powell AJ. Clinical role, accuracy, and technical aspects of cardiovascular magnetic resonance imaging in infants. Am J Cardiol 2004;94:69–74.[CrossRef][Medline]
- Gross PM, Whipp BJ, Davidson JT, Koyal SN, Wasserman K. Role of the carotid bodies in the heart rate response to breath holding in man. J Appl Physiol 1976;41:336–340.[Abstract/Free Full Text]
- Cooper HE, Parkes MJ, Clutton-Brock TH. CO2-dependent components of sinus arrhythmia from the start of breath holding in humans. Am J Physiol Heart Circ Physiol 2003;285:H841–H848.[Abstract/Free Full Text]
- Odegard KC, DiNardo JA, Tsai-Goodman B, Powell AJ, Geva T, Laussen PC. Anaesthesia considerations for cardiac MRI in infants and small children. Paediatr Anaesth 2004;14:471–476.[CrossRef][Medline]
- Holmqvist C, Larsson EM, Stahlberg F, Laurin S. Contrast-enhanced thoracic 3D-MR angiography in infants and children. Acta Radiol 2001;42:50–58.[Medline]
- Grist TM, Thornton FJ. Magnetic resonance angiography in children: technique, indications, and imaging findings. Pediatr Radiol 2005;35:26–39.[CrossRef][Medline]
- Oppelt AG, Barfub R, Fischer H, Hartl H, Schajor W. FISP: a new fast MRI sequence. Electromedica 1986;54:15–18.
- Muthupillai R, Vick GW 3rd, Flamm SD, Chung T. Time-resolved contrast-enhanced magnetic resonance angiography in pediatric patients using sensitivity encoding. J Magn Reson Imaging 2003;17:559–564.[CrossRef][Medline]
- Chung T. Magnetic resonance angiography of the body in pediatric patients: experience with a contrast-enhanced time-resolved technique. Pediatr Radiol 2005;35:3–10.[CrossRef][Medline]
- Nikolaou K, Flohr T, Knez A, et al. Advances in cardiac CT imaging: 64-slice scanner. Int J Cardiovasc Imaging 2004;20:535–540.[CrossRef][Medline]
- Jakobs TF, Wintersperger BJ, Becker CR. MDCT-imaging of peripheral arterial disease. Semin Ultrasound CT MR 2004;25:145–155.[CrossRef][Medline]
- Flohr T, Stierstorfer K, Raupach R, Ulzheimer S, Bruder H. Performance evaluation of a 64-slice CT system with z-flying focal spot. Rofo 2004;176:1803–1810.[Medline]
TOP
ABSTRACT
INTRODUCTION
