- The benefit/risk ratio must be considered when ordering imaging procedures.This demands knowledge of the pathophysiology of disease.
- skull radiographs are requested for head trauma in young infants when 50% of epidural/subdural hematomas occur in babies who do not have a skull fracture or abnormality visible on the skull examination.
- Ninety-five percent ??????of pneumonia in infants and toddlers younger than 2 years is viral. The radiographic findings show peribronchial cuffing, subsegmental atelectasis, and sometimes, hyperexpansion: the same findings as in spasmodic airway disease . Yet, we frequently obtain chest radiographs
and treat the patients with antibiotics - We must understand that the radiologic resolution of pneumonia or empyema lags behind the clinical changes, so we must avoid unnecessary, nonproductive short-interval imaging
- In the unusual case of pneumonia when it is necessary to reimage, the repeat examination
should not occur until 21 days after diagnosis (assuming that the child responds
appropriately). - In empyema, complete resolution may take months, and interval radiographs are necessary only for clinical worsening
- Another blatant example of overuse of imaging is in the child who presents with abdominal
pain and constipation. Constipation is a clinical symptom and does not need radiographic confirmation or quantification - The dose varies by age, but for single-view chest examinations,it should be 3 to 15 mrad.we should use a dose as low as reasonably achievable to obtain diagnostic images: the ALARA principle.
- We must learn to trust our physical examination.
- There is agreement that doses of radiation that cause deterministic effects (>2 Gy) are harmful. There is also considerable evidence that doses of radiation lower than 10 mGy may cause cancer [9]. These are the doses (10 mGy–100 mGy) of higher-dose CT and cumulative dose of multiple CT examinations. We do know that the younger the age at radiation exposure, the greater the lifetime risk of excess cancers [14]. However, the question of whether a safe dose of radiation exists is probably not answerable
- Radiation units (metrics)
1. Absorbed dose (ie, absorbed by the patient)
Units: the Gray (Gy) and the rad (rad)
1 Gy ¼ 100 rad
1 cGy ¼ 1 rad (cGy is a centiGray)
10 mGy ¼ 1 rad (mGy is a milliGray)
1 mGy ¼ 100 mrad
2. Equivalent dose: a measured or calculated dose
Units: the Sievert (Sv) and the rem (rem)
1 Sv ¼ 100 rema
10 mSv ¼ 1 rema
B. Background radiation
1. The total background radiation is 300–350 mrad/y, about 1 mrad/d
2. 50% is environmental, with radon accounting for 37% of that 50%
3. 50% is man-made and almost all of it is medical. CT accounts for 24% of that 50%, even
although it is <15% of all medical imaging. The CT dose index of a brain CT varies with
age but is between 1500 and 3500 mrad in a child younger than 15 y. Compare this
figure with the table below for abdomen and chests radiographs
C. Charts of the dose ranges for abdomen and chest radiographs at various ages accepted at
the Children’s Hospital of Michigan. These dose ranges are reviewed and altered as lower
techniques are devised - Abdomen dose image chart
Dose range (mrad) Supine Prone Upright
Age 0–2 y 20–35 20–28 30–50
Age 3–5 y 30–50 30–45 45–70
Age 6–10 y 40–55 40–60 45–90
Patient weight exceeding 45 kg (100 lb) ¼ use adult protocol
Age 11–18þ y 35–70 30–55 40–85
Chest dose image chart
Dose range (mrad) Anteroposterior/Posteroanterior Lateral
Age 0–2 y 5.0–8.0 6.0–10.0
Age 3–5 y 8.0–11.0 8.0–11.0
Age 6–10 y 8.0–13.0 10.0–22.0
Patient weight exceeding 45 kg (100 lb) ¼ use adult protocol
Age 11–18þ y 6.0–12.0 12.0–22.0
aFor practical purposes, with c rays (radiographs), a rem equals a rad.
Data from T. Slovis, L. Baird, C. Suggs, personal communication, 2011