Role of USG and Doppler in Imaging Orbital Disease

"""
Comprehensive PDF: Role of USG and Doppler in Orbital Disease Imaging
Generated with ReportLab
"""

from reportlab.lib.pagesizes import A4
from reportlab.lib import colors
from reportlab.lib.units import cm, mm
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.enums import TA_LEFT, TA_CENTER, TA_JUSTIFY
from reportlab.platypus import (
    SimpleDocTemplate, Paragraph, Spacer, Table, TableStyle,
    HRFlowable, PageBreak, KeepTogether
)
from reportlab.platypus.flowables import Flowable
from reportlab.lib.colors import HexColor
import os

OUTPUT_PATH = "/tmp/workspace/orbital-usg-pdf/Orbital_USG_Doppler_Summary.pdf"

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    title="Orbital USG & Doppler - Comprehensive Summary",
    author="Orris Medical",
    subject="Radiology - Orbital Imaging"
)

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# ═══════════════════════════════════════════════════════════════════════════════
# CONTENT ASSEMBLY
# ═══════════════════════════════════════════════════════════════════════════════
story = []

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                            "ORBITAL USG & COLOR DOPPLER IMAGING")
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                            "Techniques · Doppler Indices · Disease Patterns · Clinical Applications")
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story.append(Spacer(1, 0.5*cm))

# ─── INTRODUCTION ─────────────────────────────────────────────────────────────
story += section_header("1.  INTRODUCTION & OVERVIEW")
story.append(Paragraph(
    "Ultrasound (USG) is a first-line, non-invasive, radiation-free imaging modality for the orbit. "
    "The fluid-filled globe and retrobulbar fat provide an excellent acoustic window for evaluating "
    "both intraocular and retro-ocular structures. When combined with Color Doppler Imaging (CDI), "
    "it yields real-time morphological AND hemodynamic information that no other single modality "
    "can provide at the bedside. This document summarises technical principles, Doppler indices, "
    "and specific disease patterns encountered in orbital imaging.", sBody))
story.append(Spacer(1, 0.1*cm))

adv_rows = [
    ["Non-invasive / Radiation-free", "Safe in children, pregnant women, repeated examinations"],
    ["Real-time dynamic imaging", "Valsalva manoeuvre, eye movement studies possible"],
    ["Bedside availability", "ICU, emergency department use; no patient transfer needed"],
    ["Hemodynamic data", "Only modality providing real-time orbital blood-flow velocities"],
    ["Serial monitoring", "Glaucoma, thyroid eye disease, CCF post-embolisation follow-up"],
    ["Guided procedures", "Aspiration/biopsy of orbital masses under direct visualisation"],
]
story.append(make_table(
    ["Advantage", "Clinical Relevance"],
    adv_rows,
    col_widths=[CONTENT_WIDTH*0.38, CONTENT_WIDTH*0.62]
))
story.append(Spacer(1, 0.3*cm))

# ─── TECHNICAL ASPECTS ────────────────────────────────────────────────────────
story += section_header("2.  TECHNICAL ASPECTS")

story.append(Paragraph("2.1  Equipment & Setup", sH2))
equip_rows = [
    ["Probe frequency", "7.5 – 10 MHz linear array (high-frequency for superficial structures)"],
    ["Imaging depth", "1.5 – 4.0 cm (globe to orbital apex)"],
    ["Mode", "Duplex: 2D B-mode + color-coded Doppler (CDI)"],
    ["Patient position", "Supine, head elevated 30°, eyes gently closed, looking straight ahead"],
    ["Probe placement", "Horizontal over closed eyelid; MINIMAL pressure to avoid vessel compression"],
    ["Coupling medium", "Ultrasound gel with transparent plastic film barrier over lids"],
]
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    ["Parameter", "Specification"],
    equip_rows,
    col_widths=[CONTENT_WIDTH*0.3, CONTENT_WIDTH*0.7]
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story.append(Spacer(1, 0.2*cm))

story.append(Paragraph("2.2  Pre-examination Precautions", sH2))
for b in [
    "Avoid smoking / alcohol at least 12 hours before CDI (alters retrobulbar hemodynamics)",
    "Discontinue topical anti-glaucoma medications if feasible (influence orbital blood flow)",
    "Control hypertension, anxiety, tachycardia before study (affect hemodynamic indices)",
    "<b>Absolute contraindication:</b> Open globe / penetrating/perforating trauma — direct contact forbidden",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.2*cm))

story.append(Paragraph("2.3  Orbital Vessels Assessed", sH2))
vessel_rows = [
    ["Ophthalmic Artery (OA)",
     "Nasal orbit; crosses optic nerve at 35–36 mm depth; diameter 0.7–1.5 mm",
     "Moderate–high resistance; rapid systolic peak with dichotomous notch"],
    ["Central Retinal Artery (CRA)",
     "Within the optic nerve sheath; enters nerve ~10–12 mm behind globe",
     "Low resistance; continuous diastolic flow"],
    ["Short Posterior Ciliary Arteries (SPCA)",
     "Multiple vessels; pierce sclera around optic nerve",
     "Low–moderate resistance flow"],
    ["Superior Ophthalmic Vein (SOV)",
     "Passes through superior orbital fissure to cavernous sinus",
     "Low-velocity venous (non-pulsatile) flow; reversal is pathological"],
    ["Central Retinal Vein (CRV)",
     "Exits with the CRA from the optic nerve",
     "Low-velocity venous flow"],
]
story.append(make_table(
    ["Vessel", "Anatomy", "Normal Flow Pattern"],
    vessel_rows,
    col_widths=[CONTENT_WIDTH*0.25, CONTENT_WIDTH*0.38, CONTENT_WIDTH*0.37]
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story.append(Spacer(1, 0.2*cm))

story.append(Paragraph("2.4  Key Doppler Indices", sH2))
story.append(Paragraph(
    "Spectral (pulsed-wave) Doppler analysis of the orbital arteries yields the following indices:", sBody))

idx_rows = [
    ["PSV", "Peak Systolic Velocity", "Maximum velocity during systole (cm/s)"],
    ["EDV", "End-Diastolic Velocity", "Minimum velocity at end-diastole (cm/s)"],
    ["MDV", "Mean Diastolic Velocity", "Average diastolic velocity"],
    ["RI",  "Resistive Index",
     "RI = (PSV – EDV) / PSV  |  Normal OA: 0.67–0.82"],
    ["PI",  "Pulsatility Index",
     "PI = (PSV – EDV) / Mean velocity"],
    ["S/D", "Systolic / Diastolic ratio", "PSV / EDV"],
]
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    ["Index", "Full Name", "Definition / Normal Range"],
    idx_rows,
    col_widths=[CONTENT_WIDTH*0.08, CONTENT_WIDTH*0.27, CONTENT_WIDTH*0.65]
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norm_rows = [
    ["Ophthalmic Artery (OA)", "21 – 40", "3 – 9", "0.67 – 0.82"],
    ["Central Retinal Artery (CRA)", "8 – 15", "2 – 4", "0.66 – 0.75"],
    ["Short Posterior Ciliary A. (SPCA)", "8 – 12", "2 – 4", "0.55 – 0.75"],
    ["Central Retinal Vein (CRV)", "3 – 5 (venous)", "—", "—"],
]
story.append(Spacer(1, 0.2*cm))
story.append(Paragraph("Normal Reference Values:", sH3))
story.append(make_table(
    ["Vessel", "PSV (cm/s)", "EDV (cm/s)", "RI"],
    norm_rows,
    col_widths=[CONTENT_WIDTH*0.4, CONTENT_WIDTH*0.2, CONTENT_WIDTH*0.2, CONTENT_WIDTH*0.2]
))
story.append(Spacer(1, 0.15*cm))
story.append(Paragraph(
    "Note: Values vary slightly across studies; insonation angle must be <60° for valid measurements.", sNote))

# ─── PAGE BREAK ───────────────────────────────────────────────────────────────
story.append(PageBreak())

# ─── INTRAOCULAR DISEASES ─────────────────────────────────────────────────────
story += section_header("3.  USG / CDI IN INTRAOCULAR DISEASES")

story.append(Paragraph("3.1  Retinoblastoma", sH2))
for b in [
    "<b>B-mode:</b> Echogenic intraocular mass with high-amplitude echoes; <b>acoustic shadowing due to calcification</b> — pathognomonic finding",
    "<b>CDI:</b> Rich internal vascularity; elevated PSV and low RI within tumour vessels",
    "Most common primary intraocular malignancy in children (usually <5 years)",
    "Bilateral in 30%; may simulate endophthalmitis, coloboma, persistent foetal vasculature",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("3.2  Choroidal Melanoma", sH2))
for b in [
    "<b>B-mode:</b> Dome-shaped or collar-stud ('mushroom') solid mass from choroid; low-to-medium internal reflectivity",
    "Characteristic 'choroidal excavation' sign and acoustic quiet zone",
    "<b>CDI:</b> Internal blood flow present — distinguishes from haemorrhagic lesion (avascular)",
    "Most common primary intraocular malignancy in adults",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("3.3  Retinal Detachment vs Vitreous Haemorrhage", sH2))
det_rows = [
    ["Retinal Detachment",
     "Thin, highly reflective membrane; V-shaped or funnel configuration; attached at optic disc and ora serrata",
     "CRA flow extends into detached retina (confirms identity)"],
    ["Vitreous Haemorrhage",
     "Fine, low-amplitude mobile echoes within vitreous cavity; no membrane attachment",
     "Avascular — no colour Doppler signal within the echoes"],
    ["PVD (Posterior Vitreous Detachment)",
     "Thin mobile membrane not reaching ora serrata; 'ring' at optic disc",
     "No blood flow in membrane"],
    ["Choroidal Detachment",
     "Smooth, convex-bulging membranes; peripheral; 'kissing' configuration in severe cases",
     "Absence of flow (haemorrhagic) or moderate flow (exudative)"],
]
story.append(make_table(
    ["Condition", "B-mode Findings", "CDI Finding"],
    det_rows,
    col_widths=[CONTENT_WIDTH*0.25, CONTENT_WIDTH*0.42, CONTENT_WIDTH*0.33]
))
story.append(Spacer(1, 0.2*cm))

story.append(Paragraph("3.4  Posterior Scleritis", sH2))
for b in [
    "B-mode: Thickening of posterior sclera/choroid; subretinal fluid; flat choroidal detachment",
    "<b>'T-sign'</b> (or 'V-sign'): Fluid in Tenon's capsule around the optic nerve — pathognomonic",
    "CDI: Increased vascularity in inflamed choroid-scleral complex",
]:
    story.append(bullet(b))

story.append(Spacer(1, 0.3*cm))

# ─── VASCULAR LESIONS ─────────────────────────────────────────────────────────
story += section_header("4.  USG / CDI IN ORBITAL VASCULAR LESIONS")

story.append(Paragraph("4.1  Cavernous Hemangioma (Most common benign orbital tumour in adults)", sH2))
for b in [
    "<b>B-mode:</b> Well-defined, ovoid, <b>intraconal</b> mass; smooth margins; medium-to-high internal echogenicity; slow enlargement",
    "<b>CDI (KEY finding):</b> <b>Absent or minimal internal vascularity</b> — diagnostically distinguishes it from malignant tumours",
    "No bony erosion; gradual painless proptosis typical presentation",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("4.2  Capillary (Infantile) Hemangioma", sH2))
for b in [
    "<b>B-mode:</b> Hyperechoic, ill-defined mass; usually anterior to globe in eyelid / periorbital region",
    "<b>CDI:</b> <b>Rich internal vascularity</b> — multiple tortuous channels; low-resistance, high-flow pattern",
    "Present at birth / infancy; involutes by age 7–10 years",
    "Doppler helps monitor response to propranolol / steroid therapy",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("4.3  Lymphangioma / Venous Malformation", sH2))
for b in [
    "B-mode: Irregular multi-cystic lesion with fluid–fluid levels (haemorrhage within cysts = 'chocolate cysts')",
    "<b>CDI:</b> Absent or minimal internal flow — distinguishes from capillary hemangioma",
    "Enlarges during URTI; proptosis worsens with crying / Valsalva",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("4.4  Orbital Varix", sH2))
for b in [
    "<b>B-mode:</b> Compressible, hypoechoic tortuous vascular channel that <b>expands markedly with Valsalva manoeuvre</b> — pathognomonic dynamic test",
    "CDI: Venous low-velocity flow; no arterialisation",
    "Intermittent proptosis precipitated by bending forward / Valsalva",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("4.5  Carotid-Cavernous Fistula (CCF)", sH2))
story.append(Paragraph(
    "CCF is one of the most clinically important applications of orbital CDI:", sBody))
for b in [
    "<b>B-mode:</b> Dilated, tortuous Superior Ophthalmic Vein (SOV); proptosis",
    "<b>CDI — Key finding 1:</b> <b>Reversal of blood-flow direction in the SOV</b> (normally flows posteriorly to cavernous sinus; in CCF flows anteriorly toward globe)",
    "<b>CDI — Key finding 2:</b> <b>Arterialized waveform in SOV</b> — high-velocity, pulsatile, low-resistance flow within a vein",
    "Direct (high-flow) CCF: Sudden pulsatile proptosis, bruit, chemosis; dramatic CDI changes",
    "Indirect (dural, low-flow) CCF: Gradual proptosis, subtle CDI changes",
    "Gold standard for treatment planning: <b>Carotid angiography</b>; CDI is valuable for non-invasive screening and post-embolisation follow-up",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("4.6  Arteriovenous Malformation (AVM)", sH2))
for b in [
    "CDI: High-velocity, low-resistance arterial signals in multiple feeding vessels",
    "Turbulent mosaic colour pattern within the nidus",
]:
    story.append(bullet(b))

story.append(PageBreak())

# ─── THYROID EYE DISEASE ──────────────────────────────────────────────────────
story += section_header("5.  THYROID EYE DISEASE (Graves' Orbitopathy)")
for b in [
    "<b>B-mode:</b> Fusiform enlargement of extraocular muscles (EOMs) — spindle-shaped with <b>tendon sparing</b>",
    "Muscles affected in order (mnemonic: <b>I'M SLow</b>): Inferior > Medial > Superior > Lateral rectus",
    "Orbital fat expansion — diffusely echogenic retrobulbar fat",
    "<b>CDI:</b> Increased vascularity within enlarged muscles; elevated PSV in orbital vessels correlates with disease activity",
    "Serial CDI: Vascularity decreases with successful radioiodine / steroid / decompression therapy — useful treatment-response monitoring",
    "CDI Doppler can assess optic nerve compression risk at the orbital apex",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.3*cm))

# ─── OPTIC NERVE ──────────────────────────────────────────────────────────────
story += section_header("6.  OPTIC NERVE LESIONS")

story.append(Paragraph("6.1  Optic Neuritis", sH2))
for b in [
    "B-mode: Enlarged optic nerve sheath (>5 mm suggests raised ICP); hypoechoic nerve oedema",
    "<b>CDI:</b> Reduced CRA and SPCA flow; decreased PSV — correlates with degree of visual impairment",
    "Dynamic test: ONSD (Optic Nerve Sheath Diameter) measured 3 mm behind the globe",
    "<b>ONSD >5.0 mm</b> correlates with raised intracranial pressure (important emergency application)",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("6.2  Optic Nerve Sheath Meningioma", sH2))
for b in [
    "B-mode: Tubular thickening around the optic nerve; <b>'tram-track' sign</b> — parallel hyperechoic lines flanking the nerve; acoustic shadowing from calcification",
    "CDI: Increased peripheral vascularity in the meningioma",
    "Middle-aged women; slowly progressive visual loss with proptosis",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("6.3  Optic Nerve Glioma", sH2))
for b in [
    "B-mode: Fusiform enlargement of optic nerve with tortuous course; homogeneous low echogenicity",
    "Associated with neurofibromatosis type 1 (NF-1) in children",
    "CDI: Moderate internal vascularity",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.3*cm))

# ─── INFECTIONS & INFLAMMATION ────────────────────────────────────────────────
story += section_header("7.  ORBITAL INFECTIONS & INFLAMMATORY DISEASE")

story.append(Paragraph("7.1  Orbital Cellulitis & Subperiosteal Abscess", sH2))
for b in [
    "<b>Preseptal cellulitis:</b> Diffuse thickening of soft tissues anterior to orbital septum; no retrobulbar involvement",
    "<b>Postseptal / Orbital cellulitis:</b> Echogenic infiltrate posterior to septum; displacement of globe",
    "<b>Subperiosteal abscess:</b> Hypo-/anechoic collection medial to medial rectus (usually from ethmoiditis); displaces globe",
    "CDI: Hypervascularity in inflamed peri-orbital tissues",
    "USG-guided needle aspiration distinguishes abscess from cellulitis and can guide drainage",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("7.2  Idiopathic Orbital Inflammatory Syndrome (Orbital Pseudotumour)", sH2))
for b in [
    "B-mode: Poorly defined diffuse orbital infiltrate; may involve any compartment; sclerosing form highly reflective",
    "CDI: Increased vascularity in affected tissue",
    "Responds dramatically to steroids — therapeutic trial has diagnostic value",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.3*cm))

# ─── VASCULAR / ISCHAEMIC CONDITIONS ─────────────────────────────────────────
story += section_header("8.  ISCHAEMIC & VASCULAR OPTIC NEUROPATHIES")

story.append(Paragraph("8.1  Arteritic AION — Giant Cell Arteritis (GCA)", sH2))
for b in [
    "CDI: Marked bilateral reduction in orbital blood flow",
    "<b>Absence of flow in Long Posterior Ciliary Arteries (LPCA)</b> — hallmark finding",
    "Very high flow in OA (collateral compensation); altered CRA flow",
    "Important predictor of impending A-AION — warrants <b>urgent systemic corticosteroids</b>",
    "Temporal artery CDI: 'Halo sign' (hypoechoic wall thickening) may be visible",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("8.2  Non-Arteritic AION (NA-AION)", sH2))
for b in [
    "CDI: Unilateral reduction in CRA and SPCA flow; decreased EDV with elevated RI",
    "Associated with small optic disc ('disc-at-risk'), hypertension, sleep apnoea",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("8.3  Central Retinal Artery Occlusion (CRAO)", sH2))
for b in [
    "CDI: <b>Absent or markedly reduced CRA flow</b> (colour box shows no signal within CRA lumen)",
    "Spectral waveform: Absent EDV; 'to-and-fro' pattern in severe cases",
    "Retinal echogenicity increased (oedema); may detect embolus",
]:
    story.append(bullet(b))
story.append(Spacer(1, 0.15*cm))

story.append(Paragraph("8.4  Glaucoma", sH2))
for b in [
    "CDI: Increased RI in CRA and SPCA; reduced EDV in OA and CRA",
    "Reduced PSV and EDV in SPCA correlate with visual field loss and optic nerve cupping",
    "Used for <b>prognostication and serial follow-up</b> in glaucoma management",
    "Pre-perimetric glaucoma detection possible with CDI before clinical VF defects appear",
]:
    story.append(bullet(b))

story.append(PageBreak())

# ─── ORBITAL TUMOURS ──────────────────────────────────────────────────────────
story += section_header("9.  ORBITAL TUMOURS — USG / CDI PATTERNS")

tumour_rows = [
    ["Cavernous Hemangioma",
     "Well-defined; ovoid; intraconal; medium-high echogenicity",
     "Absent / minimal flow",
     "Benign; most common in adults"],
    ["Capillary Hemangioma",
     "Hyperechoic; ill-defined; anterior; periorbital",
     "Rich flow; tortuous vessels; low RI",
     "Infants; involutes spontaneously"],
    ["Lymphoma",
     "Lobulated; homogeneous; hypoechoic; moulds to globe ('cast' sign)",
     "Moderate vascularity",
     "Adults; bilateral in 20%"],
    ["Rhabdomyosarcoma",
     "Solid; heterogeneous; extraconal; rapid growth",
     "Rich internal vascularity",
     "Most common primary orbital malignancy in children"],
    ["Dermoid Cyst",
     "Well-defined; anechoic/echolucent; posterior enhancement; no calcification",
     "Avascular",
     "Congenital; superolateral quadrant"],
    ["Schwannoma / Neurofibroma",
     "Well-defined; intraconal / extraconal; medium echogenicity",
     "Mild-moderate vascularity",
     "Associated with NF-1/NF-2"],
    ["Lacrimal Gland Pleomorphic Adenoma",
     "Well-defined; lobulated; echogenic; superolateral",
     "Mild vascularity",
     "Benign; risk of malignant transformation"],
    ["Metastasis",
     "Irregular; poorly defined; may have surrounding oedema",
     "Variable; often increased flow",
     "Breast, lung, prostate most common"],
    ["Lymphangioma",
     "Multi-cystic; fluid–fluid levels; irregular margins",
     "Absent / minimal",
     "Children; worsens with URTI"],
]
story.append(make_table(
    ["Tumour", "B-mode Features", "CDI Vascularity", "Key Notes"],
    tumour_rows,
    col_widths=[CONTENT_WIDTH*0.22, CONTENT_WIDTH*0.32, CONTENT_WIDTH*0.18, CONTENT_WIDTH*0.28]
))
story.append(Spacer(1, 0.3*cm))

# ─── SUMMARY DOPPLER TABLE ────────────────────────────────────────────────────
story += section_header("10.  QUICK-REFERENCE: KEY DOPPLER FINDINGS BY DISEASE")

quick_rows = [
    ["Carotid-Cavernous Fistula (CCF)",
     "Reversed, arterialized high-velocity pulsatile flow in SOV; dilated SOV"],
    ["Capillary Hemangioma",
     "Rich internal flow; multiple tortuous channels; low RI"],
    ["Cavernous Hemangioma",
     "Absent / minimal internal vascularity (key distinguishing feature)"],
    ["Orbital Varix",
     "Venous flow; dramatic expansion with Valsalva; no arterialisation"],
    ["Giant Cell Arteritis (A-AION)",
     "Absent LPCA flow; bilateral orbital flow reduction; high OA velocity"],
    ["CRAO",
     "Absent / 'to-and-fro' CRA waveform; no EDV"],
    ["Retinoblastoma",
     "High-velocity tumour vessels; calcific shadowing on B-mode"],
    ["Glaucoma",
     "Elevated RI in CRA/SPCA; reduced EDV in OA; reduced PSV"],
    ["Thyroid Eye Disease",
     "Increased EOM vascularity; elevated PSV in orbital vessels"],
    ["Optic Neuritis",
     "Reduced CRA / SPCA PSV; enlarged optic nerve sheath (ONSD >5 mm)"],
    ["Posterior Scleritis",
     "Hypervascular choroid-sclera; 'T-sign' on B-mode"],
    ["AVM",
     "High-velocity low-resistance arterial signals in multiple vessels; turbulent mosaic"],
]
story.append(make_table(
    ["Clinical Condition", "Key CDI / Doppler Finding"],
    quick_rows,
    col_widths=[CONTENT_WIDTH*0.38, CONTENT_WIDTH*0.62]
))
story.append(Spacer(1, 0.3*cm))

# ─── LIMITATIONS ──────────────────────────────────────────────────────────────
story += section_header("11.  LIMITATIONS OF ORBITAL USG / CDI")

lim_rows = [
    ["Open globe injury", "Absolute contraindication — risk of globe compression and herniation"],
    ["Posterior orbit / apex", "Poorly visualised — CT/MRI superior for orbital apex lesions"],
    ["Bony detail", "CT is superior for bony erosion, fractures, calcification characterisation"],
    ["Operator dependence", "Significant skill required; inter-observer variability in Doppler measurements"],
    ["Acoustic shadowing", "Dense calcification limits posterior orbital evaluation"],
    ["Insonation angle errors", "Angle >60° leads to velocity underestimation — critical technique point"],
    ["Deep intracranial extension", "CT/MRI mandatory for assessing intracranial spread of orbital lesions"],
]
story.append(make_table(
    ["Limitation", "Clinical Implication"],
    lim_rows,
    col_widths=[CONTENT_WIDTH*0.3, CONTENT_WIDTH*0.7]
))
story.append(Spacer(1, 0.3*cm))

# ─── ORBITAL IMAGING ALGORITHM ────────────────────────────────────────────────
story += section_header("12.  ROLE OF USG IN ORBITAL IMAGING ALGORITHM")
story.append(Paragraph(
    "USG/CDI is typically employed as the <b>first-line</b> modality followed by CT or MRI for "
    "comprehensive characterisation. The algorithm below outlines clinical integration:", sBody))

algo_rows = [
    ["Step 1 — Initial Assessment",
     "B-mode USG: Morphology, echogenicity, calcification, retro-bulbar extension, optic nerve diameter"],
    ["Step 2 — Vascular Characterisation",
     "CDI: Vascularity (absent/mild/rich), flow direction (SOV reversal?), spectral waveform analysis"],
    ["Step 3A — Bony / Calcific Lesion",
     "HRCT orbit: Bony erosion, fracture, calcification, orbital apex involvement"],
    ["Step 3B — Soft Tissue Characterisation",
     "MRI orbit (with contrast): Tissue planes, perineural spread, intracranial extension, lesion composition"],
    ["Step 4 — Vascular Intervention",
     "CT/MR Angiography or conventional angiography for CCF, AVM, surgical planning"],
    ["Follow-up",
     "Serial USG/CDI for glaucoma, thyroid eye disease, CCF post-embolisation, haemangioma treatment"],
]
story.append(make_table(
    ["Step", "Modality / Purpose"],
    algo_rows,
    col_widths=[CONTENT_WIDTH*0.3, CONTENT_WIDTH*0.7]
))
story.append(Spacer(1, 0.4*cm))

# ─── REFERENCES ───────────────────────────────────────────────────────────────
story += section_header("REFERENCES")
refs = [
    "StatPearls — Orbital Color Doppler Imaging (NBK572120). NCBI Bookshelf, 2024.",
    "EyeWiki — Imaging in Orbit and Oculoplasty. American Academy of Ophthalmology, 2024.",
    "Grainger & Allison's Diagnostic Radiology (7th ed.) — Chapter 60: Imaging of the Orbit. Elsevier, 2021.",
    "Modrzejewska M. Guidelines for Ultrasound Examination in Ophthalmology. Part III: Color Doppler Ultrasonography. J Ultrason. 2019;19:128–136.",
    "Erickson SJ et al. Color Doppler flow imaging of the normal and abnormal orbit. Radiology. 1989;173:511–516.",
    "Venturini M et al. Orbital color Doppler ultrasound as noninvasive tool in diagnosis of CCF. Radiol Med. 2016;121:301–307.",
]
for i, r in enumerate(refs, 1):
    story.append(Paragraph(f"{i}.  {r}", sNote))
    story.append(Spacer(1, 0.05*cm))

story.append(Spacer(1, 0.5*cm))
story.append(hline(ACCENT, 0.8))
story.append(Paragraph(
    "This document is intended for educational purposes. Clinical decisions should be guided by "
    "current institutional protocols and specialist review.  |  Orris Medical  |  August 2026",
    sFooter))

# ═══════════════════════════════════════════════════════════════════════════════
# BUILD
# ═══════════════════════════════════════════════════════════════════════════════
doc.build(story, onFirstPage=add_page_number, onLaterPages=add_page_number)
print(f"PDF generated: {OUTPUT_PATH}")
print(f"File size: {os.path.getsize(OUTPUT_PATH):,} bytes")