Sedation in Pediatric Neuroimaging: The Science and the Art

RichardS. Boyer1

From the Department of Pediatric Medical Imaging, Primary Children's Medical Center, Salt Lake City, UT

Recent advances in imaging technology have The focus is on safety and efficacy using a limited revolutionized the evaluation of infants and chil­ number of familiar drugs in a methodical ap­ dren with neurologic diseases ( 1). Each of the proach. Whether using sedation several times a currently used modalities, with the exception of day or once a month, the challenge is the same­ real-time ultrasound (US), requires a motionless to control patient motion safely and effectively in patient. The advent of computed tomography infants and children in order to allow the acqui­ (CT) in the 1970s required radiologists to become sition of optimal diagnostic images. increasingly involved in pediatric sedation to al­ low the long acquisition times required by the early-generation CT scanners (2). As technology Predictability vs Safety improved and faster scanners became routinely Sleep produced by a natural (nonpharmacol­ available, the need for sedation for CT was ogic) approach is inherently safer, though less avoided in most children. predictable, than medication-induced sedation. However, in the past 6 years, the increasing Therefore, whenever possible, a natural form of use of magnetic resonance (MR) imaging in pe­ sleep is preferable to pharmacologic sedation. In diatric neurodiagnosis has necessitated a reluc­ the infant, a well-timed feeding, a warm blanket tant return to the frequent use of sedation for and a quiet, dark room may stimulate a post­ pediatric brain and spine examinations. In pedi­ prandial nap that is sufficient for a noninvasive atric centers, this return has been reasonably well imaging study. However, scanners are busy and tolerated because of the greater comfort level of schedules cannot usually accommodate the lack pediatric radiologists with the challenges of se­ of predictability required by the natural approach. dation and of monitoring children, and the greater In addition, long exam times and external stimuli availability of pediatric-trained technologists and may awaken the infant and terminate the exam nurses. In contrast, personnel at many primarily prematurely. Therefore, the pharmacologic ap­ adult MR facilities now find themselves faced with proach to sedation is usually preferred for its the need to perform occasional pediatric studies, predictability. and feel discomfort or anxiety in sedating children Predictability must not be at the expense of safely. safety for the child. Safety is the most important This paper is written for those using sedation consideration in pediatric sedation. Elements of to perform the occasional neuroimaging study on an approach to pediatric sedation that favor an infant or child. The major emphasis is directed safety include: toward sedation for MR, but the basic principles 1. establishment of a written protocol in each also apply in CT, angiography, and myelography. imaging department that follows the guide­ lines for pediatric sedation developed by 1 Address reprint requests to Dr Boyer, Department of Pediatric Med­ the American Academy of Pediatrics Sec­ ical imaging, Primary Children's Medical Center, 100 North Medical Drive, tion on Anesthesiology (3) specifically ad­ Salt Lake City, UT 84 11 3. dressing such issues as candidates for se­ Index terms: Patients, sedation; Chloral hydrate; Pediatric neurora8 iology dation, facilities, equipment, informed con­ I AJNR 13:777-783, Mar/ Apr 1992 0195-6 108/ 92/1302-0777 sent, drugs and dosages, documentation, © American Society of Neuroradiology personnel, monitoring procedures, recov- 777 778 AJNR: 13, March/Apri11992

ery care, discharge criteria, and emer­ detailed consideration of the pharmacology of the gency contingencies; agents commonly used for pediatric sedation is 2. direct physician involvement in the seda­ beyond the scope of this article. Interested read­ tion process; ers are referred to standard reference texts and 3. limiting the number of drugs used for se­ pertinent review articles (4). dation to a few with which all involved Table 1 lists some common pediatric sedative personnel can become very familiar; drugs used in our department with dosage guide­ 4. regular quality assurance evaluation of lines and comments. Table 2 summarizes the complications, sedation failures, adverse order of our preferences for sedation in the dif­ reactions, and other negative outcomes ferent neuroimaging modalities stratified by pa­ with appropriate modification of protocols tient weight. and procedures; 5. routine use of state-of-the-art monitoring equipment, especially in MR , where direct MR visualization of the sedated child is more In our imaging department at a children's hos­ difficult; and pital, the most frequent use of sedation is for MR 6. employment of properly-trained person- · studies of the head, neck and spine. Children nel, preferably nurses or specially-trained under age 7 or 8 years of age are routinely technologists, to care for sedated patients. sedated, though we have had exceptionally co­ operative children as young as age 3 undergo an Techniques MR study without sedation. Pediatric sedation must be tailored to the pa­ Sleep deprivation is an important adjunct to tient, the examination, and the clinical setting. A sedation with any drug regardless of the imaging

TABLE 1: Commonly used drugs for pediatric sedation'

Drug Route Dose Comments

Chloral hydrate P.O. or gastric 75 mg/kg (initial) Good results at this dose tube 25 mg/kg (supplement if not Safe asleep in 30 min) Many years experience Maximum total dose 2000 Flavored syrup · mg

Sodium pentobarbital IV or IM 5-6 mg/kg (initial) IV more predictable and (Nembutal) 2-3 mg/kg (supplement shorter recovery after 30 min prn) Maximum total dose 200 mg

Na lbuphine (Nubain) IV 0.1 mg/ kg m ixed with 0.05- Less predictable in younger + 0.1 mg/ kg children Midazolam (Versed) May repeat X 2 prn Maximum effect lasts ap- Maximum total Versed dose proximately 30 min 5 mg Partially reversed by Naloxone Nubain is a partial agonist of other narcotics

"Ca rdiac cocktail" IM 25 mg (0 .5 mL) Good analgesia Meperidine (Demerol) 6.25 mg (0 .25 mL) Longer action (often >2 hr) Promethazine 6.25 mg (0.25 mL) More risk respiratory depres- (Phenergan) D9se per Table 3 sion Chlorpromazine Partially reversed by (Thorazine) Naloxone

Sodium thiopental Rectal 25 mg/ kg Does not require IV access (Pentothal) Repeat lh dose in 15 min Onset 7-15 min prn

• Note.-Abbreviations: IV, intravenous; IM, intramuscular; prn, pro re na'ta ("'as circumstances may require"); P.O., per os ("'by mouth"). AJNR: 13, March/ April 1992 779

TABLE 2: Sedation preferences for pediatric neuroimaging

Modality Patient Group Order of Preference Comments

us Infants 1. None Sedation rarely nec­ 2. Chloral hydrate essary

MR Infants- small children 1. Chloral hydrate Reduce dose in neo­ (0-25 kg) 2. Nembutal nates 3. Cardiac cocktail

Larger children-ado­ 1. Nembutal, Penta- Most children under lescents (25+ kg) thai 8 require sedation 2. Cardiac cocktail or Sedation usually not Nubain + Versed required, but if se­ 3. General anesthesia dation is required , this is the most dif­ ficult group

CT Infants-young chil­ 1. Immobilization Sedation rarely re­ dren 2. Chloral hydrate quired for routine 3. Nembutal exams Sedation may be necessary for 3-D or thin section studies

Older children-ado­ 1. Television Sedation rarely lescents 2. Versed + Nubain needed unless pa­ 3. Nembutal tient is neurologi­ cally impaired

Angiography Infants-children 1. Cardiac cocktail See Table 3 (0-40 kg)

Older children-ado­ 1. Nubain + Versed lescents (40 kg+) 2. Demerol (1 mg/ kg) + Phenergan (.5 mg/ kg)

M yelography Infants-young chil­ 1. Cardiac cocktail dren 0-7 yr 2. Nubain + Versed

Older children-ado­ 1. None Sedation rarely lescents 2. Nubain + Versed needed unless neu­ rologica lly im­ paired

modality (5). Our protocol for sleep deprivation Oral chloral hydrate is the most frequently used is to keep the child up approximately 2 hours drug for pediatric sedation in North American after the usual bedtime at night and awaken them pediatric centers (6). In our pediatric MR experi­ 1 to 2 hours earlier than usual in the morning. ence since September 1986, representing more The child is not allowed to nap either in the car than 3000 sedated studies, chloral hydrate with on the way to the exam or while in the waiting sleep deprivation has been successful in over room. For afternoon studies, the usual morning 90% of sedation attempts. Our results agree with nap is denied. We even sleep-deprive older chil­ those of a recent report (7) in which sedation with dren scheduled for MR examinations even though an average dose of 58 mg/kg (range 25-81 mg/ no sedation is planned. The monotonous sounds kg) of chloral hydrate was successful on the first of the MR scanner will often put to sleep a tired attempt in 86% of 50 children. We use a routine but nonsedated patient, allowing for a better dose of 75 mg/kg to a maximum of 2000 mg. study. An additional 25 mg/kg may be given if the 780 AJNR: 13, March/April 1992 patient does not go to sleep in 30 minutes after of the infant or young child (see below), allow the first dose. The use of higher doses of chloral routine CT examinations to be performed on hydrate has been reported (8) but is associated infants and small children, with a surprisingly with increased frequency of side effects, espe­ small number of repeat scans being necessary cially vomiting and hyperactivity. Our initial dose and with little or no motion artifact. Safety and of chloral hydrate is reduced to 50-60 mg/kg for throughput are both enhanced by this nonsedated neonates, patients recently started on sedative approach to CT. When sedation is required for doses of anticonvulsant medications, and for chil­ CT, the approach is similar to that previously dren who are lethargic before the medication is described for MR. given. Flavored preparations of chloral hydrate The art of immobilizing a nonsedated infant is are reasonably palatable. We have also found that accomplished by: 1) wrapping the child in a a popsicle given after the liquid chloral hydrate receiving blanket folded into a triangle with the "helps the medicine go down." Occasionally, the shoulders across the widest portion of the triangle medication is administered through an oral or and the points folded over the arms and under nasogastric tube. Infants and young children are the body; 2) securing the child on the scan table allowed clear liquids after their sedative dose, with restraints over the chest and knees and a because an empty stomach makes it harder for sandbag under the knees to keep the child from them to sleep. To our knowledge, we have had sliding down; and 3) immobilizing the head in its no episodes of aspiration related to this practice. holder with a combination of rectangular and Patients who fail chloral hydrate sedation or triangular sponges and adhesive tape pulled who are too large to receive an adequate dose/ tightly across the head holder and forehead. kg within the 2000-mg guideline, are more of a challenge to sedate. Our second-line drug in MR is pentobarbital (9) administered either intramus­ Angiography and Myelography cularly or (preferably) intravenously in doses up Angiography and myelography, though be­ to 6 mg/kg ( 10). Rectal thiopental 25 mg/kg, coming less commonly used because of advances though not as commonly used nationwide, is also in MR imaging and MR angiography, are special a useful second-line drug in this setting and does situations requiring analgesia in addition to se­ not require intravenous access ( 11 ). Older chil­ dation. In infants and you_ng children, we prefer dren and adolescents who require sedation for a combination of meperidine, chlorpromazine, MR usually respond to a combination of mida­ and promethazine ("cardiac cocktail") for these zolam (12) and nalbuphine (13). General anes­ studies. Table 3 provides a dose schedule for this thesia is reserved for the most refractory cases combination in patients weighing up to 40 kg. and requires specialized equipment and monitor­ The prolonged sedative effect of this cardiac ing. cocktail may be helpful in these longer proce­ dures and continues into the recovery period.

Ultrasound and CT TABLE 3: Cardiac cocktail dosage schedule Sedation is rarely required for US examinations Mix/ per ml: Meperidine (Demerol) 25 mg (0.5 ml) of the head or spine and for routine CT exami­ Chlorpromazine (Thorazine) 6.25 mg (0.25 ml) nations of the head. Sedation in CT is reserved Prometazine (Phenergan) 6.25 mg (0.25 ml) for thin-section studies as of the temporal bone or for 3-D reconstruction, when coronal position­ Dosage scale (administer deep IM)" 2.5 kg (5 lbs) 0.17 ml ·ing is required, or when the patient has significant 4.5 kg (10 lbs) 0.33 ml neurologic impairment. We have found that a 6.8 kg (15 lbs) 0.5 ml television monitor suspended from the ceiling of 9.0 kg (20 lbs) 0.67 ml the CT scanning room connected to a video . 11.4 kg (25 lbs) 0.83 ml cassette recorder in the control room provides 13.6 kg (30 lbs) 1.0 ml 18.3 kg (40 lbs) 1.22 ml adequate distraction for most neurologically nor­ 22.7 kg (50 lbs) 1.47 ml mal children 3 years and older, almost completely 27.3 kg (60 lbs) 1.70 ml eliminating the need for sedation in this group. A 31 .8 kg (70 lbs) 1 .80 ml patient technologist carefully watching a fussy 36.4 kg (80 lbs) 1.90 ml child and pushing the scan button at just the right 40.1 kg (90 lbs) 2.0 ml moment, combined with effective immobilization • Note.-IM, intramuscular. AJNR: 13, March/April1992 781

However, the duration of sedation may be long scanner and the comforting presence of a parent enough to be a problem in some patients (4). or other care-giver are helpful. A reassuring hand General anesthesia for angiography is an expen­ on their leg during the exam may obviate the sive luxury to be used only in patients refractory need for sedation. Some MR scanners have a to routine sedative drugs or for interventional pause button, which can be judiciously used to procedures. successfully scan a "wiggly" child. Routine angiography can be performed in older When the decision is made to sedate the child, children and teenagers with combinations of me­ careful explanation of expected effects, possible peridine and promethazine or nalbuphine and complications, and alternative choices to the par­ midazolam. We have been particularly pleased ent or guardian is essential. Institutions vary as with our results with the latter combination in this to whether to obtain written informed consent for group. Teenagers are particularly prone to vagal­ routine sedation in noninvasive exams (6). Re­ mediated hypotension during angiography when gardless, information must be shared and consent only lightly sedated. We have found that wrap­ to proceed be obtained. A brief medical hi~tory ping the legs with elastic bandages prior to the with attention to current medications, history of procedure is helpful in preventing this problem. airway problems, chronic cardiac or respiratory Older children rarely require sedation for myelog­ disorders, and any concurrent illness is obtained raphy when an affirmative, supportive approach by the nurse or technologist. If necessary, con­ is used. sultation with the radiologist and/or referring phy­ sician precedes administration of sedation. Before Sedation Monitoring Regardless of the examination to be performed I and the sedation approach planned, preparation Once sedated, and until adequately recovered, of the patient and family is essential. Referring the child requires careful attention to monitoring physicians offices and hospital units must prop­ and safety. The airway is protected by extension erly instruct patients and parents regarding sleep of the neck. Occasionally an oral airway is nec­ deprivation, withholding of food and water (3) essary to prevent the tongue from obstructing (see Table 4), proper clothing to wear, and what breathing. Oxygen is a very useful adjunct to to expect from the exam. In our experience, a sedation. In an editorial commentary from an phone call to the parent by a nurse or technologist anesthesiologist's perspective, Fisher (14) rec­ on the day prior to the examination is valuable in ommended administration of oxygen to all se­ confirming that this information has been accu­ dated patients (with the possible exceptions of rately communicated and in answering questions premature neonates at risk for retinopathy and and concerns. Printed literature and specially­ patients with abnormal ventilatory responses to prepared video presentations are also helpful in oxygen). Oxygen administered by such simple educating parents and children. devices as nasal prongs or a mask . "markedly Evaluation of the patient by a nurse, technol­ increases pulmonary oxygen reserves and per­ ogist and/or physician is helpful in determining mits prolonged apnea or airway obstruction with­ whether sedation is required, and if so, what out hypoxia." Furthermore, "its benefits are great, regimen is optimal. Review of previous sedation it is inexpensive, and it is not toxic (when admin­ records (kept in the folder with previous imaging istered briefly to healthy patients)". studies) is essential. MR studies can be performe_d Monitoring sedated patients in MR continues on many children in the 5- to 8-year range with­ to be a challenge. But monitoring is essential. out sedation using an affirmative approach. Al­ Initial experience with monitoring in MR was lowing them to observe another child in the MR limited to plastic stethoscopes with long tubing to listen to heart sounds, taping a cup on the TABLE 4: NPO guidelines for pediatric sedation (3) chest of a sedated child to watch respirations,

1. No milk or solids after midnight and direct observation by a nurse, technologist or parent lying in the scanner with the child. More 2. Clear liquids prior to exam as follows: recently, apnea monitors measuring expired car­ Age 0-2 yr Up to 4 hr before bon dioxide content and pulse oximeters have 3-6 yr Up to 6 hr before added greatly to our ability to monitor patients in 7+ yr Up to 8 hr before MR. Shellack (15) has reviewed av~ilabili!¥· use, 782 AJNR: 13, March/April1992 and· limitations of these devices. Simple tech­ limit their imaging studies to US and CT (when niques for radio frequency shielding of the detec­ necessary), rarely performing MR on a premature tor and wires of a pulse oximeter may be helpful neonate. In our department, an MR exam on any in preventing artifacts (16, 17). Rare instances of child in the first month of life requires specific skin burns have occurred from monitoring wires radiologist approval. Hypothermia may be . pre­ coiled under or around a part of the sedated child vented by covering the neonate's head, wrapping while he is lying in the changing magnetic flux of the child in plastic or bubble wrap, and monitoring the MR scanner ( 18). temperature ( 19). Continuous monitoring, frequent observation, Infants and children with underlying diseases, airway care and protection against aspiration con­ especially cardiac and/or respiratory, are at tinue after completion of the examination until greater risk for complications from sedation. We the child is satisfactorily recovered. Carefully­ frequently consult with referring physicians on a prepared guidelines are available to assist in de­ case-by-case basis to be certain they have termining a child's suitability for discharge after weighed the risks of sedation against the value of sedation (3). Discharge instructions are reviewed the information to be gained. with a family member or care-giver and are con­ Occasionally, a child with an undiagnosed brain firmed in writing, translated into the appropriate tumor or other cause of increased intracranial language if necessary. Hydration is occasionally pressure will be sedated for an imaging study. a problem in infants and younger children kept When this potentially dangerous situation is rec­ "N.P.O. (nothing by mouth)" for a prolonged time. ognized, the child must be very carefully moni­ Fluids may be administered via a gastric tube or tored until the examination is completed and an intravenous catheter. Dehydration prolongs appropriate measures immediately instituted to recovery from sedatives and should be corrected prevent hypoventilation and to decrease intracra­ before it becomes a problem. nial pressure.

Special Considerations Choice of Sedative Brief consideration of some miscellaneous The judicious physician will limit his or her points related to pediatric sedation may be helpful choices for sedation to a small number of agents to those with less experience in this arena. in order to become thoroughly familiar with their dosages, side effects, idiosyncrasies, and con­ traindications. The broad spectrum of drugs and Sedation Failure combinations of drugs used for sedation in this In spite of one's best efforts, sedation failures country attest to the fact that there are many occur. They are more frequent when instructions ways to satisfactorily accomplish the task (6). regarding sleep deprivation are not followed, in mentally impaired older children, and with sub­ optimal doses of medication. We inform parents Chloral Hydrate Controversy prior to administration of a sedative drug that, if Concern was recently raised regarding animal it does not work, we have alternative choices for mutagenicity of chloral hydrate in a letter to the sedation, one of which will be successful. We editor of Science (20). Citing data that have been prefer to begin with the least toxic drug(s) that available in the literature for several years, a we think will be sufficient in each case. Only concerned father who is a "consultant in toxicol­ rarely do we mix sedative regimens, preferring to ogy" pointed out that "chloral hydrate is a toxic reschedule the patient for another day rather than metabolite of the rodent carcinogen trichloroeth­ risk a polypharmacy approach to sedation. Gen­ ylene (TCE) and is a mutagen and chromosome eral anesthesia is rarely needed, but may be the damaging agent." only resort is some patients. · We have not changed our use of chloral hy­ drate or felt the need to discuss this issue with parents prior to using it for pediatric sedation. In High Risk Patients my unofficial survey of 40 North American pe­ Certain patients require extra care when se­ diatric radiologists (personal communications) dated. Premature infants are at risk in the hostile 61 % of those responding were aware of this environment of the MR scanner. We prefer to controversy. Of those who were aware of the AJNR: 13, March/Apri11992 783

letter, 78% have not changed their approach to duce excellent results and facilitate application of the use of chloral hydrate. Of those who have current imaging technology in the diagnosis of changed, they indicated that they now use intra­ pediatric neurologic disease. venous pentobarbital and rectal thiopental far more frequently than before. Only 8% discussed the controversy with parents. Acknowledgments My conversations with regional officials of the I extend appreciation to Valerie Kemp for secretarial Food and Drug Administration (FDA) indicate assistance and to Cheryl Fitzgerald, RT, for technical as­ that there is no new policy or recommendation sistance. regarding chloral hydrate (personal communica­ tion with the Public Affairs Office of U.S. Food References and Drug Administration, Denver, CO). I feel that chloral hydrate is the safest, most effective agent 1. Barkovich AJ. Pediatric neuroimaging. New York: Raven Press, 1990: for pediatric sedation in most infants and young 1 2. Thompson JR, Schneider S, Ashwal S, Holden BS, Hinshaw DB Jr, children and, therefore, will continue to use it Hasso AN. Choice of sedation for computed tomography in children: unless instructed otherwise by the FDA, another a prospective evaluation. Radiology 1982;143:475-479 government agency, or by the pharmaceutical 3. American Academy of Pediatrics-Committee on Drugs, Section on manufacturer. Anesthesiology. Guidelines for the elective use of conscious sedation, deep sedation, and general anesthesia in pediatric patients. Pediatrics 1985;76:317-321 Parents 4. Nahata MC. Sedation in ped iatric patients undergoing diagnostic procedures. Drug Intel/ Clin Pharm 1988;22:711-715 The participation of parents in the care of their 5. Barkovich AJ. Techniques and methods in pediatric magnetic reso­ children during sedation and imaging studies is a nance imaging. Semin Ultrasound CT MR 1988;9:186-191 double-edged sword. Parents are often very help­ 6. Keeter S, Benator RM, Weinberg SM, Hartenberg MA. Sedation in ful in supplying important medical information, pediatric CT: national survey of current practice. Radiology 1990; 175:745-752 assisting in calming or holding a child before and 7. Rumm PO , Takao RT, Fox OJ, et al. Efficacy of sedation of children after scanning, and have a right to be involved in . with chloral hydrate. South Med J 1990;83: 1040-1042 their child's care. Therefore, we allow one parent 8. Patel M, Leonidas JC, Newman GG, Dickinson D, Golden B. High or guardian to accompany the child through the dose chloralhydrate: a safe and effective sedative for pediatric MRI entire process of sedation, scanning, and recov­ and CT. Paper presented at the 29th Annual Meeting of the American Society of Neuroradiology. Washington, DC, June 9-14, 1991 ery for MR and CT. However, parents may oc­ 9. Merrick PA, Case BJ, Jagjivan B, Stackman T J. Care of pediatric casionally be somewhat difficult or even obstruc­ patients sedated with pentobarbital sodium in MRI. Pediatr Nurs 1991 ; tive to the efforts of nurses, technologists, and 17:34-38 physicians. In this setting, we endeavor to tact­ 10. Strain JD, Campbell JB, Harvey LA, Campbell JB. IV Nembutal: safe fully explain our perception of the situation to the sedation for children undergoing CT. AJR 1988; 151 :975-979 11 . Burckart GJ, White T J Ill , Seigle RL, Jabbour JT, Ramey DR. Rectal parents and invite them to retire to the waiting thiopental versus an intramuscular cocktail for sedating children room until the exam is completed. Most under­ before computerized tomography. Am J Hasp Pharm 1980;37: stand and are willing to cooperate. 222-224 12. Diament MJ, Stanley P. The use of midazolam for sedation of infants and children. AJR 1988;150:377-378 Summary 13. Glanville JN. Nalpuhine hydrochloride (Nubain, DuPont) as premedi­ cation for radiological procedures. Clin Radiol1990;42:212-213 Sedation of infants and children for neuroim­ 14. Fisher OM. Sedation of pediatric patients: An anesthesiologist's per­ aging is a "necessary evil" that will be with us for spective [comment[. Radiology 1990; 175:613-615 the foreseeable future. Sedation must be accom­ 15. Shellack FG. Monitoring sedated pediatric patients during MR imaging panied safely in all patients with a high frequency [letter[. Radiology 1990; 177:586-587 16. Wagle WA. Technique for RF isolation of a pulse oximeter in a 1.5 T of success on the first attempt. A carefully-con­ MR unit [letter[. AJNR 1989;10:208 sidered written sedation plan that addresses the 17. Fisher OM, Litt L, Cote CJ. Use of pulse oximetry during MR imaging issues raised in this review will assure maximum of pediatric patients [l etter]. Radiology 1991 ;178:891-892 safety and success in sedating infants and chil­ 18. Kana! E, Shellack FG, Talagala L. Safety considerations in MR dren at each facility involved in pediatric neuroim­ imaging. Radiology 1990; 176:593-606 19. McArdle CB, Richardson CF, Nicholes DA, et al. Developmental aging. An affirmative approach and careful atten­ features of the neonatal brain: MR imaging. I. Gray-white matter tion to both the science and the art of pediatric differentiation and myelination. Radiology 1987; 162:223-229 sedation by all concerned professionals will pro- 20. Smith MT. Ch loral hydrate warning [letter]. Science 1990; 19:359