Important Figures


  • Background radiation 2.4mSv/yr (0.3 internal/diet, 0.4 cosmic rays, 0.5 terrestrial, 1.2 radon).
  • Typical doses – PA CXR 0.02mSv (BERT 3 days), CT chest or abdo 10mSv (BERT 7yrs).
  • Dose limits – Public 1mSv/yr, occupational 20mSv/yr.
  • T1 – Short TR (<1000ms, contrast develops in early regrowth), short TE (<45ms).
  • T2 – Long TR (>2000ms), long TE (>60ms, to allow spin dephasing).
  • PD – Long TR (>2000ms), short TE (<45ms), to reduce T1 and T2 weightings.


  • Tonsillar herniation >/=5mm below foramen magnum (up to 6mm normal in 5-15yo).
  • Midline shift significant >/= 3mm.
  • [[Paediatric_Neuroimaging#Neurocutaneous_Syndromes|Neurocutaneous Syndromes]] – NF1, NF2, TS, Sturge-Weber, CHL, basal cell naevus, Cowden, Parry Romberg, meningiomatosis, neurocutaneous melanosis, HHT.
  • LeFort I through all maxillary walls; II medial and inferior orbit, superior and lateral maxilla; III medial and lateral orbit, zygomatic arch.
  • MRS – Normal ascending stair-step of similar Cho then Cr, then higher NAA peaks. High Cho in membrane synthesis/degradation (tumour esp meningioma, infection). Cr is used as reference. NAA marker of neuronal integrity, reduced with neuronal death, elevated with Canavan disease. Lactate doublet peaks in anaerobic metabolism (acute ischaemia, seizure, high grade tumour/infection).
  • CTP/MRP – Infarct with CBF <10mL/100g/min or DWI positive; ischaemic penumbra 10-20; oligaemic (not at risk) 30-50; normal 45-110. Penumbra >20% of infarct tends to be treated.
  • Haemangiopericytoma vs meningioma – Consider when >40mm, bony destruction.
  • Choroid plexus calcification pathological <10yo.
  • Pineal calcification pathological <6yo or >10mm.
  • Pineal cysts >10mm should be followed up.
  • Pituitary maximum height 9mm women, 8mm men, 6mm <12yo; up to 12mm in physiologic hypertrophy (puberty, pregnancy, lactation).
  • Microadenoma </=10mm, macroadenomas >10mm. Cavernous invasion if extends lateral to lateral wall cavernous ICA or >50% circumferential.
  • Infundibulum should be same or smaller than adjacent basilar artery.

Extracranial Head and Neck Imaging

  • H&N SCC staging (except peri-glottic, nasopharyngeal tumours) – T1 </=20mm greatest dimension; T2 20-40mm; T3 >40mm; T4 local spread; N1 single ipsilateral </=30mm; N2a single 30-60mm; N2b multiple ipsilateral; N2c bilateral/contralateral; N3 any >60mm.
  • Choanal atresia <5mm neonates, <10mm adults.

Chest Imaging

  • PA CXR – 140kVp, FFD 1.8m
  • PAH – PA systolic >30mmHg.

7th Edition AJCC Classification (includes NSCLC, small cell and carcinoid): I-IIIa resectable, ie disease with supraclavicular or contralateral mediastinal nodes, contralateral lung deposits or malignant effusions are unresectable.

  • Stage 0 – AIS is <30mm.
  • Stage IA – T1 <30mm greatest dimension.
  • Stage IB – T2a 30-50mm.
  • Stage IIA – T2b 50-70mm. T1-T2a N1 (ipsilateral hilar/intrapulmonary nodes).
  • Stage IIB – T2b N1. T3 >70mm or invades chest wall, diphragm, phrenic nerve, mediastinal pleural, parietal pericardium, bronchus <20mm from carina, separate nodules in same lobe.
  • Stage IIIA – T1-T2 N2 (ipsilateral mediastinal/subcarinal). T3 N1-2. T4 N0-1, invades mediastinum, heart, great vessels, trachea, reccurent laryngeal nerve, oesophagus, vertebral body, carina, nodules in different ipsilateral lobe.
  • Stage IIIB – T4 N2-3. Any N3 (contralateral mediastinal/hilar nodes, supraclavicular/low cervical nodes).
  • Stage IV – M1 nodules in contralateral lung, pleural nodules, malignant pleural/pericardial effusion, distant metastases.

Flieshner guidelines for incidentally detected nodules at nonscreening CT:

  • </= 4mm – Low risk (minimal/no smoking hisotry) no followup; high risk (smoking) 12 months then stop.
  • 4-6mm – Low risk 12 months then stop; high risk 6-12 months then 18-24 months.
  • 6-8mm – Low risk 6-12 months then 18-24 months; high risk 3-6 months, 9-12 months then 24 months
  • >8mm – Both followup at 3, 9 and 24months, dynamic CECT, PET and/or biopsy.

Breast Imaging

  • ~30kV, density 1.6-1.8, 4 film series is 1mGy. Cancer mortality risk 2:million in age 40-49yo, 1:million 50-59yo.
  • NZ screening mammography every 2yrs for 45-69yo.
  • Core biopsy usually 14G.
  • Nottingham criteria for adequate sample is at least 5 calcifications total, or calcifications in at least 3 cores (out of 5).
  • Giant fibroadenomas >30mm.
  • AJCC staging: 0 DCIS/LCIS; I <20mm; II 20-50mm or 1-3 axillary nodes; III >50mm or >3/other nodes; IV metastases including supraclavicular nodes.

Abdominal Imaging

  • GIST benign <40-50mm, malignant >50-100mm.
  • Infectious enterocolitis – Small bowel: viruses (Noravirus, Rotavirus), Whipple disease, Cholera. Terminal ileum: Yersinia, Typhoid. Colitis: Salmonella, Campylobacter, E.coli, Shigella (descending and occasionally ileum), pseudomembranous.
  • Polyps <5mm usually hyperplastic, >5mm usually adenomas, >10mm 10% malignant, >20mm 50% malignant.
  • Appendicitis >6mm (outer to outer wall).
  • Biliary dilatation – Intrahepatic >40% portal vein or >2mm; CBD >6-7mm + 1mm/decade >60yo.
  • Hepatomegaly >155mm midclavicular line.
  • Splenomagally >140mm length, >60mm thickeness.
  • Renal size 90-130mm.
  • Cirrhotic nodues: Regenerative <10mm low/iso T2 with no hyperenhancement; dysplastic >10mm; HCC >10mm, high T2, hypervascular and/or washout.
  • Hilar Cholangiocarcinoma Bismuth-Corlette classification: I >20mm distal to RHD/LHD; II involving confluence; IIIa/b RHD/LHD; IV RHD and LHD.
  • GB polyps >10mm may be malignant.
  • [[Small_and_Large_Bowel#Polyposis_Syndromes|Polyposis Syndromes]] – Adenomas: FAP including Gardner and Turcot. Hamartomas: Peutz-Jeghers, pTEN (incl Cowden), juvenile polyposis, Cronkhite-Canada. HNPCC.
  • Pancreatic cancer nonresectability criteria: beyond pancreatic margins, nodes >15mm, encasement/obstruction of vessels.
  • Pancreatic microcystic serous cystadenoma <20mm cysts; macrocystic >20mm.
  • Adrenal adenoma <40mm, <10HU. Absolute percentage washout (APW) >60% being (PV-delayed)/(PV-unenhanced). Relative percentage washout (RPW) >40% being (PV-delayed)/PV.
  • [[Adrenals#Multiple Endocrine Neoplasia (MEN) Syndromes|MEN Syndromes]] – MEN1 parathyroids, pancreatic, pituitary prolactinoma, duodenal gastrinoma. MEN2A pheo, thyroid medullary, parathyroid hyperplasia. MEN2B pheo, thyroid medullary, neuromas/ganglioneuromas. MEN2 familial medullary thyroid.
  • AML >40mm treated with resection or embolisation.
  • Bosniak classification – I Benign simple cyst. II minimally complicated (thin septation, calcification, hyperdense). IIF follow-up (3, 6, 12 months). III biopsy (irregular/thickened/enhancing septa or calcification). IV malignant (irregular thick wall, enhancing mass).
  • Testis 2x3x4cm, epedidymal head 8mm.
  • Testicular germ cell tumours LDH for tumour mass, AFP yolk sac, HCG choriocarcinoma elements.
  • Testicular staging: I confined to testis; II retroperitoneal nodes; III elsewhere.
  • Prostate <30mL.

Colorectal AJCC TNM Staging:

  • Stage 0 – Tis intramucosal or invasion of lamina propria.
  • Stage I (Dukes A) – T1 ivades submucosa. T2 invades muscularis propria.
  • Stage II (Dukes B) – T3 invades pericolorectal tissues. T4 invades to visceral peritoneum (4a) or invades/adherant to other organs/structures (4b).
  • Stage III (Dukes C) – N1 1-3 regional nodes. N2 >/= 4 nodes.
  • Stage IV – Metastases limited to one organ (M1a) or >1 organ/site or peritoneum (M1b).

RCC Staging:

  • Stage I – Confined to renal capsule. T1 <25mm, T2 >25mm.
  • Stage II – T3a perinephric fat but within renal fascia.
  • Stage IIIa – T3b renal vein, T3c IVC below diaphragm, T4b IVC above diaphragm.
  • Stage IIIb – Local nodes >15mm.
  • Stage IIIc – Local nodes and tumour thrombus.
  • Stage IVa – T4a direct invasion of adjacent organs.
  • Stage IVb – Distant metastases.

Gynaecology Imaging

  • Uterus maximum dimensions 80 x 60 x 40mm, less in postmenopausal.
  • Endometrium proliferative/oestrogen phase 4-8mm; secretory/progesterone phase 15mm; end menstruation 2-4mm; postmenomausal <5mm.
  • Ovaries maximum 40mm in any one direction, 6-10mL menstruating, 3-6mL postmenopausal, can be up to 20mL (esp pregnancy).

Cervical cancer staging:

  • Stage 0 – In situ.
  • Stage I – Confined to cervix. Ia <5mm deep and <7mm wide; Ib >5mm deep or >7mm wide.
  • Stage II – Beyond cervix or invasion of upper 2/3 vagina. IIa without parametrial invasion; IIb with parametrial invasion.
  • Stage III – To pelvic wall, lower 1/3 vagina or hydronephrosis. IIIa no extension to pelvic side wall; IIIb to pelvic side wall or hydronephrosis.
  • Stage IV – IVa invasion of mucosa of bladder/rectum or pelvic side walls; IVb distant metastases, para-aortic or inguinal lymphadenopathy.

Endometrial cancer staging:

  • Stage 0 – In situ.
  • Stage I – Limited to uterus. Ia <50% thickness myometrium; Ic >50%.
  • Stage II – Cervix. IIa cervical mucosa; IIb cervical stroma.
  • Stage III – Outside uterus. IIIa parametrial fat or positive peritoneal cytology; IIIb vagina; IIIc regional lymphadenopathy.
  • Stage IV – Outside true pelvis or into bladder/rectum. IVa bladder/bowel mucosa; IVb distant metastases, malignant ascites, peritoneal seeding or abdominal/inguinal lymphadenopathy.

Ovarian cancer staging:

  • Stage I – Limited to ovaries. Ia to one ovary; Ib to both ovaries; Ic malignant ascites or peritoneal washings.
  • Stage II – Pelvic extension. IIa uterus and/or fallopian tubes; IIb other pelvic tissues; IIc with malignant ascites or peritoneal washings.
  • Stage III – Peritoneal extension outside pelvis or LN. IIIa microscopic peritoneal metastases outside pelvis; IIIb macroscopic <20mm; IIIc >20mm and/or regional LN.
  • Stage IV – Distant metastases.

Obstetric Imaging

  • GA in days ~ MSD + 25, CRL + 42 (±3/7).
  • Yolk sac 2-6mm.
  • ASUM criteria for failed pregnancy on TV scanning: embryo not seen when MSD >/=25mm, heart activity not seen when CRL >/=7mm.
  • ‘First trimester oligohydramnios’ – MSD – CRL is <5mm.
  • NT can be done CRL 45-84mm, always increased risk >2.5mm.
  • GA = 4 x BPD (cm) + 1; ~50mm at 20/40, ~100mm at 40/40.
  • GA in weeks ~ cerebellum/renal length (mm).
  • Cisterna magna 2-10mm.
  • Ventricles </= 10mm.
  • Nuchal fold thickened if >/= 6mm.
  • FHR >90bpm at 5-6/40, or >120bpm >8/40.
  • MCA RI >0.7. Vmax abnormal >70cm/s.
  • Pericardial effusion >2mm; 2-7mm may be OK if isolated.
  • Thoracic:abdominal circumference >0.75.
  • Hydronephrosis – AP pelvis >5mm before 20/40, >10mm after 20/40.
  • Femur:foot length >/= 0.9 (less suggests skeletal dysplasia).
  • Low lying placenta <20mm (2nd T) or <40mm (3rd T).
  • AFI 5-20cm, deepest pocket 2-8cm.
  • Chorionic fold (synechiae, Di-Di) >/=2mm thick.
  • Cervical length normal 30-50mm, short if <25mm.
  • Trisomy 18 rocker bottom foot, cleched hand, radial ray, stippled epiphyses, choroid plexus cysts, horeshoe kidney. Trisomy 13 holoprosencephaly, polydactyly, rockerbottom foot, clenched had with overlapping digits. Turners horseshoe kidney, cystic hygroma, hashimoto, streak ovaries.

Musculoskeletal Imaging

  • Magic angle effect/phenomenon – Signal when 55o to β0 on short-TE (GRE, T1, PD).
  • AC injury: Grade 1 XR N; grade 2 AC >5mm; grade 3 coracoclavicular >12mm; grade 4 dislocation of clavicle.
  • Bigliani types of acromion arch: type 1 flat; type 2 concave anteriorly; type 3 antero-inferior hook (acute narrowing of space); type 4 convex superiorly.
  • Baumann’s angle (humeral capitellar angle) is between humeral shaft and capitellar physis (for predicting final carrying angle), normal 85-90deg, <5deg difference from contralateral.
  • Scapholunate angle on lateral (between most volar projections) 30-60deg. >60deg in scapholunate dissociation and DISI, <30deg in lunotriquetral dissociation and VISI.
  • Scapholunate interval 2-4mm.
  • Femoral neck/shaft angle 115-140deg, 15deg anteverted.
  • Symphysis pubis diastasis >5mm adults, or >10mm skeletally immature.
  • FAI alpha angle (where neck extends outside of circle over head) >50deg.
  • THJR – Lateral opening 40±10deg, anteversion 10-15deg.
  • Patella tendon:patella length ratio 0.9-1.35 (greater is alta, less is baja).
  • Trochlear groove sulcus angle (highest points femoral trochlea to deepsest groove) 138deg.
  • Anterior drawer/translocation sign (ACL tear) – Posterior tibia >7mm anterior to posterior lateral femoral condyle.
  • Bohler angle – 20-40deg.
  • BMD DEXA scan – T score -1 to -2.5 osteopenia, <-2.5 osteoporosis.
  • Giant bone island >25mm.
  • Osteoid osteoma nidus <20mm, osteoblastoma >20mm.
  • FCD <20-30mm, NOF >20-30mm.
  • Enneking staging for bone and soft tissue sarcomas – Stage Ia is G1T1M0; Ib G1T2M0; IIa G2T1M0; IIb G2T2M0; III G*T*M1. G0 benign; G1 low grade malignant; G2 high grade malignant. T0 limited by capsule; T1 single compartment; T2 extracompartment or abuts major neurovascualr structures. M0 no mets, M1 metastases.
  • McGregor’s line posterior hard palate to undersurface occiput; Chamberlain’s line hard palate to mid opisthion. If dens extends >5mm above then basilar invagination.
  • Basion-axis interval (BAI) – Post axial line (PAL) to basion <12mm.
  • Basion-dental interval (BDI) – <12mm.
  • Powers ratio – BC:AO <1.
  • Predental space <3mm adults, <5mm children.
  • Atlanto-occipital interval <1.5mm.
  • Peg type 1 at tip; 2 base; 3 into cancellous bone of body.
  • Hangman fracture Effendi type 1 undisplaced (<3mm, <15deg); 2 displaced/angulated; 3 dislocated facets.

Paediatric Imaging

  • Hypertrophic pyloric stenosis – >3mm thick, >15mm long.
  • Appendicitis – US >6mm.
  • Lung hyperexpansion >10 post or >6 ant ribs.
  • UAC high lines T8-10, low lines <L3.
  • DDH normal values – alpha angle >60deg (55 neonates); beta angle >55deg; acetabular angle <30deg at bith and <22deg at 1yo; centre-edge angle 20deg in infancy, 26-30deg in adolescence.
  • Femoral neck-shaft angle 150deg at birth, 125deg in adults
  • [[Paediatric Musculoskeletal#Congenital Foot Deformities|Foot/ankle angles]] – calcaneal pitch 20-30deg; AP talocalcaneal angle 15-40deg (30-50deg newborns); lateral talocalcaneal angle (Kite’s angle) 25-45deg (50deg newborns).

Vascular and Interventional Radiology

  • Abdominal aorta – Normal 20-25mm, ectatic 25-30mm, aneurysm >30mm. Rupture rate 1%/year 40-50mm, 10%/yr 50-60mm. Treat withn >50mm or expansion >10mm/year.
  • pANCA (MPO-ANCA) – Churg-Strauss, microscopic polyangiitis, polyarteris nodosa, UC, PSC, RA.
  • cANCA (PR3-ANCA) – Wegener granulomatosis.
  • Vasculitis Chapel Hill classification – Large vessel: GCA, Takayasu. Medium vessel: PAN, Kawasaki, Thromboangiitis obliterans (Buerger disease). Small vessel: Wegener granulomatosis, Churg-Strauss, microscopic polyangiitis, Raynaud phenomenon.
  • ICA stenosis: 0-29% PSV <100; >30% PSV>110, EDV <40, ICA/CCA <3.2; >50% PSV>130, EDV >40, ICA/CCA >3.2; >70% PSV >230, EDV >110, ICA/CCA >4.0; >95% string flow.
  • General stenosis PSV ratio (stenosis:prox) 50% 2:1, 75% 3.5:1, 90% 7:1.

Nuclear Medicine Imaging

  • V/Q Amended PIOPED criteria: <25% of a lung segment is small, 25-75% moderate, >75% large defect. 2 moderate or 4 small defects are equivalent to a full-segment defect.
    • High – >/= 2 large mismatched segments or equivalents.
    • Intermediate – >/= 1 moderate segment or equivalent.
    • Low – Matched defects, larger CXR abnormality, stripe sign, >3 small defects, nonsegmental defects.
    • Very low – < 3 small defects.
    • Normal.
  • Thyroid RAIU normal 10-30%.
  • PET SUV physiologic generally 0.5-2.5, most malignancy 2.5-3.0.


  • Lymphoma Ann Arbor staging (esp HL): I single LN group; II >1 group; III both sides of diaphragm; IV extra-lymphatic sits (except spleen). Suffix A assymptomatic; B symptomatic; E localised extralymphatic extension.
  • NHL – Mature B cell (diffulse large = most common, Burkitt from EBV, lymphoplasmacytic, marginal zone eg MALToma/BALtoma, mantle cell, follicular), mature T cell, NK cell.
  • HL – Classical (nodular sclerosing = most, mixed cellularity, lymphyte rich, lymphocyte depletion) and lymphocytic predominance types.
  • Tumour markers: HCG (choriocarcinoma), calcitonin (medullary thyroid), AFP (HCC, yolk sac, neuroblastoma, hepatoblastoma), CEA (GIT, lung, breast), prostatic acid phosphatase PAP and PSA (prostate), CA 19-9 (pancreatic also GIT, biliary/HCC), CA 125 (ovary also gynae), CA 15-3 (breast). LDH used for general tissue breakdwon in cancer bulk esp lymphoma.
  • HPV – High risk 16, 18; low risk 6, 11.
  • Cysticercosis (Taenia solium) – Undercooked pork with cystercerci (larval cysts) -> mature in intestine. Food/water contaminated with faeces containing larvae -> hatch penetrating bowel -> larvae spread (brain, muscles, skin, heart) and cannot mature.
  • Hydatid (Echinococcus granulosus) – Dog definitive, sheep intermediate, human accidental intermediate. Contaminated food/water with eggs (dog faeces) -> hatch penetrating bowel -> larvae spread (liver, lungs, bones, brain) and cannot mature and some encyst. Outer pericyst (host fibrous capsule), exocyst (chitin), endocyst (germative layer, daughter cyst). Hydatid sand degenerating scolices. Water lily sign ruptured exocyst.
  • Schistosomiasis – Larvae penetrate skin -> lung, mature -> hepatic vessels -> portal or pelvic veins, mate, release eggs that lodge into colon or bladder walls. Eggs may transfer into stool/urine.